3070_10_AE2501B_Primer

AES2501B A ES2501B Sens Sen s o r Hard Har d w are ar e Int In t egr eg r ati at i o n Guide For USB Applic ations

Primer 3070 Rev 1.0 July 11, 2006

AuthenTec, Aut henTec, Inc. Post Office Box 2719 Melbourne, Florida 32902-2719 32902-2719 321-308-1300 www.authentec.com

3xxx Rev 1.0 (11JUL06)

Authen AuthenTec Tec welcom welcomes es your your sugge suggesti stions ons.. We We try try to make make our our publicat publication ions s usef useful, ul, intere interesti sting, ng, and inform informativ ative, e, and we hope you will take the time to help us improve them. Please send any comments or suggestions by mail or email.

Disclaimer of Warranty AUTHENTEC SOFTWARE , INCLUDING INSTRUCTIONS FOR ITS USE , IS PROVIDED “ AS IS ” WITHOUT WARRANTY OF ANY KIND . AUTHENTEC FURTHER DISCLAIMS ALL IMPLIED WARRANTIES INCLUDING WITHOUT LIMITATION ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR OF FITNESS FOR A PARTICULAR PURPOSE . THE ENTIRE RISK ARISING OUT OF THE USE OR PERFORMANCE OF THE SOFTWARE AND DOCUMENTATION REMAINS WITH YOU. IN NO EVENT SHALL AUTHENTEC, ITS AUTHORS, OR ANYONE ELSE INVOLVED IN THE CREATION, PRODUCTION, OR DELIVERY OF THE SOFTWARE BE LIABLE FOR ANY DAMAGES WHATSOEVER (INCLUDING, WITHOUT LIMITATION, DAMAGE FOR LOSS OF BUSINESS PROFITS, BUSINESS INTERRUPTION, LOSS OF BUSINESS INFORMATION, OR OTHER PECUNIARY LOSS) ARISING OUT OF THE USE OF OR INABILITY TO USE THE SOFTWARE OR DOCUMENTATION, EVEN IF AUTHENTEC HAS BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGES. BECAUSE SOME STATES OR COUNTRIES DO NOT ALLOW THE EXCLUSION OR LIMITATION OF LIABILITY FOR CONSEQUENTIAL OR INCIDENTAL DAMAGES, THE ABOVE LIMITATION MAY NOT APPLY TO YOU.

U.S. U.S. Government Restricted Rights

AuthenTec software and documentation are provided with RESTRICTED RESTRICTED RIGHTS. Use, Use, duplication, or disclosure by the government is subject to restrictions as set forth in subparagraph (c)(1)(ii) of the Rights in Technical Data and Computer Software clause at DFARS 252.227-7013 or subparagraph (c)(1) and (2) of the Commercial Computer Software – Restricted Rights 48 CFR 52.227-19, as applicable. Manufacturer is AuthenTec, Inc.; Melbourne, Melbourne, Florida 32901-2719.This Agreement is governed by the laws of the State of Florida. Au th enTec , Inc . Post Offic e Box 2719 Melbourn e, Flor ida 3290232902-271 2719 9 321-308-1300 www.authentec.com [email protected]

AuthenTec, FingerLoc, FingerLoc, EntréPad, Aware, AES1510, AES1510, AES2501A, AES2510, AES3400, AES3400, AES3500, AES3500, AES4000, AF-S2, AF-S2, ISX, TruePrint, the AuthenTec colophons and logotypes, and the phrase “Personal Security for the Real World” are trademarks of AuthenTec, Inc. Microsoft and Windows 98 are registered trademarks of Microsoft Corp. Microwire™ is a trademark of National Semiconductor Corp. SPI ™ is a registered trademark of Motorola. Motorola. All other trademarks are the property property of their respective owners.

AES2501B Har dw are Integ In teg rat io n Gu id e For USB Ap pl ic ati on s Copyright ©2006 by AuthenTec, Inc. No part of this public ation may be reproduced in any form or by any means without prior written permission. Printed in the United States of America.

3070 Rev Rev 1.0 (11JUL06)

Auth Au th enTec Co nf ident id ential ial

2

Authen AuthenTec Tec welcom welcomes es your your sugge suggesti stions ons.. We We try try to make make our our publicat publication ions s usef useful, ul, intere interesti sting, ng, and inform informativ ative, e, and we hope you will take the time to help us improve them. Please send any comments or suggestions by mail or email.

Disclaimer of Warranty AUTHENTEC SOFTWARE , INCLUDING INSTRUCTIONS FOR ITS USE , IS PROVIDED “ AS IS ” WITHOUT WARRANTY OF ANY KIND . AUTHENTEC FURTHER DISCLAIMS ALL IMPLIED WARRANTIES INCLUDING WITHOUT LIMITATION ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR OF FITNESS FOR A PARTICULAR PURPOSE . THE ENTIRE RISK ARISING OUT OF THE USE OR PERFORMANCE OF THE SOFTWARE AND DOCUMENTATION REMAINS WITH YOU. IN NO EVENT SHALL AUTHENTEC, ITS AUTHORS, OR ANYONE ELSE INVOLVED IN THE CREATION, PRODUCTION, OR DELIVERY OF THE SOFTWARE BE LIABLE FOR ANY DAMAGES WHATSOEVER (INCLUDING, WITHOUT LIMITATION, DAMAGE FOR LOSS OF BUSINESS PROFITS, BUSINESS INTERRUPTION, LOSS OF BUSINESS INFORMATION, OR OTHER PECUNIARY LOSS) ARISING OUT OF THE USE OF OR INABILITY TO USE THE SOFTWARE OR DOCUMENTATION, EVEN IF AUTHENTEC HAS BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGES. BECAUSE SOME STATES OR COUNTRIES DO NOT ALLOW THE EXCLUSION OR LIMITATION OF LIABILITY FOR CONSEQUENTIAL OR INCIDENTAL DAMAGES, THE ABOVE LIMITATION MAY NOT APPLY TO YOU.

U.S. U.S. Government Restricted Rights

AuthenTec software and documentation are provided with RESTRICTED RESTRICTED RIGHTS. Use, Use, duplication, or disclosure by the government is subject to restrictions as set forth in subparagraph (c)(1)(ii) of the Rights in Technical Data and Computer Software clause at DFARS 252.227-7013 or subparagraph (c)(1) and (2) of the Commercial Computer Software – Restricted Rights 48 CFR 52.227-19, as applicable. Manufacturer is AuthenTec, Inc.; Melbourne, Melbourne, Florida 32901-2719.This Agreement is governed by the laws of the State of Florida. Au th enTec , Inc . Post Offic e Box 2719 Melbourn e, Flor ida 3290232902-271 2719 9 321-308-1300 www.authentec.com [email protected]

AuthenTec, FingerLoc, FingerLoc, EntréPad, Aware, AES1510, AES1510, AES2501A, AES2510, AES3400, AES3400, AES3500, AES3500, AES4000, AF-S2, AF-S2, ISX, TruePrint, the AuthenTec colophons and logotypes, and the phrase “Personal Security for the Real World” are trademarks of AuthenTec, Inc. Microsoft and Windows 98 are registered trademarks of Microsoft Corp. Microwire™ is a trademark of National Semiconductor Corp. SPI ™ is a registered trademark of Motorola. Motorola. All other trademarks are the property property of their respective owners.

AES2501B Har dw are Integ In teg rat io n Gu id e For USB Ap pl ic ati on s Copyright ©2006 by AuthenTec, Inc. No part of this public ation may be reproduced in any form or by any means without prior written permission. Printed in the United States of America.

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TABLE OF CONTENTS 1

INTRODUCTION .......................... ........................................ ............................ ............................ ............................ ............................ ............................ ............................ ............................ .........................7 ...........7

1.1 1.2 1.3 1.4 1.5

2

SENSOR DESCRIPTION............................ .......................................... ............................ ............................ ............................ ............................ ............................ ............................ .........................7 ...........7 SENSOR APPLICATIONS.......................... ........................................ ............................ ............................ ............................ ............................ ............................ ............................ .........................9 ...........9 USB I NTERFACE ........................... ......................................... ............................ ............................ ............................ ............................ ............................ ............................ ............................ ....................9 ......9 SYSTEM ARCHITECTURE........................... ......................................... ............................. ............................. ............................ ............................ ............................ ............................. .....................9 ......9 I NTEGRATION PROCESS ............................ .......................................... ............................ ............................ ............................ ............................ ............................ ........................... ....................10 .......10

RESOURCES ........................... ......................................... ............................ ............................ ............................ ............................ ............................ ............................ ........................... ...........................12 ..............12

2.1 2.2 2.3 2.3.1 2.3.2 2.3.3 2.4 2.5

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THEORY OF OPERATION ........................... ......................................... ............................ ............................ ............................ ............................ ............................ ............................ ..................16 ....16

3.1 3.2 3.2.1 3.2.2 3.2.3 3.3

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SENSOR DATA TYPES ............................ .......................................... ............................ ............................ ............................ ............................ ............................ ............................ .......................17 .........17 SENSOR OPERATION I N A SYSTEM ........................... ......................................... ............................ ............................ ............................ ............................ ............................ ..................17 ....17 Finger Detect Mode ............................ ......................................... ........................... ............................ ........................... ........................... ........................... ............................ ............................17 .............17 Fingerprint Imaging Mode ........................... ......................................... ............................ ............................ ............................ ............................ ........................... ........................... ................ ..18 18 Scrolling Mode............................ Mode......................................... ........................... ............................ ............................ ........................... ........................... ............................. ............................. ....................18 ......18 FAULT DETECTION A ND CORRECTION ............................ .......................................... ............................ ............................ ............................ ............................ .........................18 ...........18

ELECTRICAL DESIGN ........................... ......................................... ............................ ............................ ............................ ............................ ............................ ............................ .........................19 ...........19

4.1 4.1.1 4.1.2 4.1.3 4.1.4 4.2 4.2.1 4.2.2 4.3 4.3.1 4.4 4.4.1 4.5 4.6 4.6.1 4.6.2

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EFERENCE DESIGN K IT IT ........................... R EFERENCE ......................................... ............................ ............................ ............................ ............................ ............................ ........................... ....................12 .......12 MANUFACTURERS I NTEGRATION K IT .......................................... ............................ ............................ ............................ ........................... ...........................13 ..............13 IT ............................ SOFTWARE DEVELOPMENT K ITS .......................................... ............................ ............................ ............................ ............................ ........................... ....................13 .......13 ITS ............................ Software Development Kit .......................... ........................................ ............................ ........................... ........................... ............................ ............................ ............................ ..................13 ....13 Preboot Authentication (PBA) Kit .......................... ........................................ ........................... ........................... ........................... ........................... ............................. .....................14 ......14 Using Third-Party Matchers............................. Matchers........................................... ............................ ............................ ............................ ............................ ............................ .........................15 ...........15 I NDUSTRIAL AND MECHANICAL DESIGN ........................... ......................................... ............................ ............................ ............................ ............................ .......................15 .........15 SIGNAL NAMING CONVENTION............................ .......................................... ............................ ............................ ............................ ............................ ............................ .......................15 .........15

POWER SUPPLY DESIGN............................ .......................................... ............................ ............................ ............................ ............................ ............................ ........................... ....................19 .......19 Supply Voltages And Currents......................... Currents...................................... ........................... ........................... ........................... ........................... .......................... ........................... ................ ..19 19 Supply Voltage Noise Requirements ........................... ......................................... ........................... ........................... ............................ ............................ ............................. ................. 19 Supply Voltage Rise Time Requirements .......................... ........................................ ........................... ........................... ........................... ........................... .........................20 ...........20 Power Control Design ........................... ......................................... ............................ ............................ ........................... ........................... ............................ ............................ .......................21 .........21 CLOCK CIRCUIT DESIGN ........................... ......................................... ............................ ............................ ............................ ............................ ............................ ........................... ....................23 .......23 Crystal Circuit Design............. Design ........................... ............................ ............................ ........................... ........................... ............................ ............................ ............................ .......................24 .........24 External Clock Circuit Design........................ Design...................................... ............................ ............................ ........................... ........................... ............................. ............................27 .............27 R ESET .......................................... ............................ ............................ ............................ ............................ ............................ ........................... ....................29 .......29 ESET CIRCUIT DESIGN ............................ Reset Timing Considerations .......................... ........................................ ............................ ............................ ............................ ............................ ........................... ...........................30 ..............30 USB I NTERFACE DESIGN ............................ .......................................... ............................ ............................ ............................ ............................ ............................ ............................ ..................31 ....31 Interface Voltages................................. Voltages.............................................. ........................... ............................ ............................ ........................... ........................... ............................ .........................31 ...........31 CHARGE PUMP FILTER ........................... ......................................... ............................ ............................ ............................ ............................ ............................ ............................ .......................31 .........31 ING CIRCUIT ........................... FINGER R ING ......................................... ............................ ............................ ............................ ............................ ............................ ............................ .......................32 .........32 TVS Characteristics and Clamping Voltage .......................... ........................................ ........................... ........................... ............................ ........................... ...................32 ......32 Chassis Ground Connection .......................... ........................................ ........................... ........................... ............................ ............................ ........................... ........................... ................ ..32 32

PCB LAYOUT CONSIDERATIONS ............................ .......................................... ............................ ............................ ............................ ............................ ............................ ................ .. 33

5.1 5.2 5.3 5.3.1 5.3.2

DECOUPLING CAPACITORS ........................... ......................................... ............................ ............................ ............................ ............................ ............................ ............................ ................ ..33 33 CRYSTAL PLACEMENT ........................... ......................................... ............................ ............................ ............................ ............................ ............................ ............................ .......................34 .........34 ESD DESIGN............................ .......................................... ............................ ............................ ............................ ............................ ............................ ............................ ............................ .......................34 .........34 TVS Device Selection .......................... ........................................ ........................... ........................... ............................ ........................... .......................... ............................ ............................35 .............35 TVS Characteristics and Clamping Voltage .......................... ........................................ ........................... ........................... ............................ ........................... ...................35 ......35

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5.3.3 5.3.4 5.4 5.5

TVS PCBA Placement......................................................................................................................................35 Casing Crevice ESD ........................................................................................................................................36 I NTERFACE SIGNALS .........................................................................................................................................37 TEST POINT.......................................................................................................................................................37

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GROUNDING AND SHIELDING ........................................................................................................................38

7

INDUSTRIAL DESIGN .........................................................................................................................................40

7.1 7.2 7.3 7.4 7.5 7.5.1 7.5.2 7.5.3 7.5.4 7.5.5 7.5.6 7.5.7 7.5.8

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DESIGN CONSIDERATIONS ................................................................................................................................40 FINGER IN CONTACT WITH SURFACE OF SENSOR ...............................................................................................41 TOP SURFACE OF CASING MATES FLUSH WITH SENSOR WINGS ..........................................................................41 MATING ALIGNMENT SHOULD NOT RELY ON THE SENSOR ITSELF ......................................................................41 DESIGN SPECIFICATIONS ..................................................................................................................................42 Entry And Exit Angles......................................................................................................................................42 Extent Of Finger Groove .................................................................................................................................45 Design For Biometric Applications .................................................................................................................46 Design For Navigation and Biometric Applications........................................................................................48 Sensor To Housing Clearance .........................................................................................................................49 Sensor Wing Design.........................................................................................................................................50 PCB to Housing Guide for Mating Alignment .................................................................................................51 Gaskets.............................................................................................................................................................52

DESIGN CHECKL ISTS ........................................................................................................................................54

8.1 8.2 8.3 8.4 8.5

9 10

GENERAL ELECTRICAL DESIGN CHECKLIST .....................................................................................................54 ESD AND GENERAL PCBA LAYOUT DESIGN CHECKLIST.................................................................................54 I NDUSTRIAL DESIGN CHECKLIST (SENSOR SURFACE TO CASING SURFACE ).......................................................55 MECHANICAL DESIGN CHECKLIST (PCBA MOUNTING & MATING TO CASING ).................................................56 PROTOTYPE OR U NIT FUNCTIONAL VALIDATION CHECKLIST ...........................................................................56

REFERENCE DESIGN

USB MODULE .....................................................................................................................................................58

10.1

11

........................................................................................................................................57

PURPOSE OF THE MODULE ...............................................................................................................................59

TROUBLESHOOTING SENSOR MODULES .................................................................................................60

11.1 11.1.1 11.1.2 11.1.3 11.1.4 11.2 11.2.1 11.2.2 11.2.3 11.3 11.4

SENSOR E NUMERATION ....................................................................................................................................60 Sensor Not Visible In Device Manager............................................................................................................63 Sensor Is Shown As An Unknown Device ........................................................................................................66 Sensor Is “Banged” In The Device Manager ..................................................................................................67 Sensor Re-Enumerates Intermittently ..............................................................................................................69 OTHER SENSOR MODULE PROBLEMS................................................................................................................70 A Fingerprint Image Cannot Be Displayed .....................................................................................................71 Sensor Becomes Uncomfortably Warm............................................................................................................72 Sensor Does Not Wake Up From Suspend .......................................................................................................73 OTHER DEBUGGING TIPS ..................................................................................................................................73 HARDWARE DEBUGGING SUMMARY ................................................................................................................74

12

GLOSSARY.........................................................................................................................................................77

13

REVISION HISTORY .........................................................................................................................................79

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LIST OF FIGURES Figure 1-1 AES2501B Sensor.......................................................................................................................... 8 Figure 1-2 System Block Diagram .................................................................................................................. 10 Figure 2-1 PBA Functional Diagram ..............................................................................................................14 Figure 3-1 Sensor Imaging Principle.............................................................................................................. 16 Figure 3-2 Stacked Image Slices ................................................................................................................... 17 Figure 4-1 VDD Ripple Measurement............................................................................................................20 Figure 4-2 Improper VDD Characteristics...................................................................................................... 21 Figure 4-3 Power Control Design (VDD)........................................................................................................ 22 Figure 4-4 Power Control Design (VDDA) .....................................................................................................23 Figure 4-5 Reset Time With Crystal Or Resonator ........................................................................................ 25 Figure 4-6 Measuring Oscillator Start-up Time .............................................................................................. 26 Figure 4-7 External Clock Using SYS_CLK Connection................................................................................ 27 Figure 4-8 Reset Timing Example With Externally-Driven Clock On SYS_CLK Pin .....................................28 Figure 4-9 External Clock Specifications ....................................................................................................... 28 Figure 4-10 Reset Circuit ...............................................................................................................................30 Figure 4-11 Reset Timing And VDD............................................................................................................... 30 Figure 4-12 USB Connections .......................................................................................................................31 Figure 4-13 Charge Pump Filter..................................................................................................................... 32 Figure 4-14 Finger Ring Circuit ...................................................................................................................... 33 Figure 5-1 Decoupling Capacitor Placement ................................................................................................. 33 Figure 5-2 Crystal Placement......................................................................................................................... 34 Figure 5-3 SR05 Placement (Ground Plane Not Shown F or Clarity)............................................................. 36 Figure 5-4 Extension Of Ground Plane Underneath Sensor Edges .............................................................. 37 Figure 5-5 Test Pad For USB OE# Signal .....................................................................................................38 Figure 7-1 Sensor Wings ...............................................................................................................................41 Figure 7-2 Housing Design Specifications .....................................................................................................43 Figure 7-3 Correct Finger Groove Design (Side View) ..................................................................................43 Figure 7-4 Incorrect Finger Groove Design (Side View) ................................................................................ 44 Figure 7-5 Finger Groove (Side View) ........................................................................................................... 45 Figure 7-6 Finger Groove Extent....................................................................................................................46 Figure 7-7 Optimal Finger Groove Design .....................................................................................................47 Figure 7-8 Optimal Flush Mating with Casing and Taper to Sensor Wings Design....................................... 47 Figure 7-9 Shortened Finger Groove .............................................................................................................48 Figure 7-10 Planar Housing Design With Guide Bumps ................................................................................49 Figure 7-11 Housing Beveled Around Sensor Wings .................................................................................... 50 Figure 7-12 Housing Bevel (Side View) ......................................................................................................... 50 Figure 7-13 Beveled Wing Areas Combined With Guide Bumps ..................................................................51 Figure 7-14 Assembly Guides For Sensor Housing....................................................................................... 52 Figure 7-15 Gasket Design ............................................................................................................................ 53 Figure 7-16 Gasket Example ......................................................................................................................... 53 Figure 9-1 USB RDK Block Diagram ............................................................................................................ 57 Figure 11-1 Sensor Enumeration (Device Manager) ..................................................................................... 61 Figure 11-2 Device Driver Properties............................................................................................................. 62 Figure 11-3 Normal Sensor Signals At Plug-In .............................................................................................. 63 Figure 11-4 Normal Sensor Signals Showing Oscillator Start-Up .................................................................64 Figure 11-5 Effect Of OVC_DET Continually Switching VDD........................................................................65 Figure 11-6 Unknown Device......................................................................................................................... 66 Figure 11-7 Disabling And Enabling The Sensor ...........................................................................................68 Figure 11-8 Marginal VDD Ripple .................................................................................................................. 70 Figure 11-9 Using DotNetDemo To Capture An Image .................................................................................71 Figure 11-10 Sensor Drive Ring Signal ......................................................................................................... 72

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LIST OF TABLES Table 2-1 RDK Documentation ......................................................................................................................12 Table 2-2 MIK Contents ................................................................................................................................. 13 Table 2-3 SDK Document Contents...............................................................................................................14 Table 4-1 OVC_DET Specifications...............................................................................................................22 Table 4-2 Clock Frequency Settings..............................................................................................................24 Table 4-3 Crystal/Resonator Specifications...................................................................................................26 Table 4-4 External Clock Specifications ........................................................................................................ 29 Table 4-5 Interface Voltages .......................................................................................................................... 31 Table 13-1 Revision History ........................................................................................................................... 79

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1

Introduction The AuthenTec AES2501B fingerprint sensor is ideally suited for USB applications like PCs, laptops, and PC peripherals. This sensor has a unique set of features that make it the perfect choice for these applications: • • • •

Extremely small size Low power operation Built-in USB 2.0 compatible full speed interface with full support for suspend and remote wakeup Built-in fault detection and recovery for ESD events

The AES2501B is a multi-function device that can provide AuthenTec’s Power of Touch ® capabilities to any product. These capabilities include greatly enhanced security through fingerprint authentication, function launch, and motion detection for menu or cursor control to replace buttons and switches. The purpose of this primer is to provide the information needed to integrate the AES2501B into a real product. This manual has been created based on industry leading practical experience with real applications in the marketplace. It shows both the things to do and the things to avoid in design and development. In order to avoid costly rework, as well as to ensure maximum reliability and performance of the sensor, this manual should This manual is intended for be studied in detail before beginning system design. hardware integrators and system designers.

1.1

Sensor Descri ptio n

The AES2501B sensor captures a fingerprint when a finger is swiped along its surface. An array of 1024 pixel elements under the surface of the sensor images the finger as it passes across the sensor. The pixels and associated electronics use the patented AuthenTec TruePrint® Technology, which provides the industry’s best ability to acquire all fingerprints, regardless of the condition of the skin. For compatibility with USB interfaces, the sensor operates with a single supply voltage of 3.0V to 3.6V.

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Figure 1-1 AES2501B Senso r

Maximum swipe speed is dependent on the USB bus bandwidth available. USB tree architecture should be considered carefully when integrating the sensor. The sensor is provided in a very small Lead-free 48 Ball Grid Array (BGA) Package. A thin package 13.8mm x 5mm x 1.2mm seated height. The sensor is extremely reliable when integrated as directed, and provides ESD Immunity to IEC 61000-4-2 Level 4 Criteria B and abrasion resistance of at least 10 million rubs with no degradation visible to the naked eye or in function. Temperature performance is compatible with USB device operation, in the 0°C to +70°C range. The AES2501B is only available in a RoHS-compliant, lead-free package. In addition to biometric capturing fingerprints, the sensor can also be used as a scrolling device, like the mouse scrolling function. This function can actually reduce system cost by replacing the buttons and switches normally used for on-screen navigation in peripherals, tablets or laptops. The AES2501B uses an image-based full scrolling technique. Scrolling parameters like speed and sensitivity are also programmable to allow for different parameters in different products. The sensor fully supports USB suspend and remote wakeup. During suspend mode, the sensor operates in a low power finger detection mode, so that touching the sensor will initiate a remote wakeup. In addition, the sensor has several built-in event detection functions that are triggered by ESD events or other disturbances that may cause the sensor to malfunction. Once a fault has been detected, the sensor will automatically recover from the fault by forcing a USB re-enumeration or a sensor master reset. The sensor also supports Biometric Boot, enabling asset and privacy protection. In BIOS applications, the sensor may be used to authenticate a user before a PC has booted up (preboot authentication). Fingerprint templates and code may be stored in the PC System Flash. The information stored in flash can be associated with an authentication word supplied by the sensor while being read by the host computer to further increase the security of the flash data. This mechanism can be used to ensure that the data that is assumed to be coming from the flash is really coming from this location, and not through some other mechanism that has been patched into the system to subvert the security.

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1.2

Sensor App licatio ns

The AES2501B is perfect for applications like: • • •

1.3

Personal Computers Laptops and tablet PCs PC peripherals like USB mice and keyboards

USB Interface

The AES2501B has a built-in USB 2.0 compatible full speed (12MHz) USB interface. The sensor is a USB device with three endpoints, and is not a host controller or hub. Further details about the sensor’s USB descriptors and strings can be found in the document EntréPad AES2501B Fingerprint Sensor Hardware Specification (document #3063).

1.4

System Arch itectur e

The overall design for a system using the AES2501B sensor is shown in the block diagram below. The sensor is connected to a host computer through its USB interface, but also is supported by various peripheral circuits that supply a clock signal, reset, and power to the sensor. In operation, the sensor captures multiple “slices” of the fingerprint as a finger is swiped over the surface of the sensor. Each slice consists of 1537 bytes of data, and a complete swipe may contain up to 113 individual slices. The swipe data is held temporarily in a secure buffer in the RAM of the computer, and then the AuthenTec fingerprint matcher software processes this data to extract information that can be used to match the fingerprint. This extracted information is called a “template”, and is much smaller in size than the original swipe data. When enrolling a user’s finger, the extracted template is stored on the host computer’s system flash or on the hard disk. When verifying a user’s fingerprint, the application presents the information extracted from the new swipe data and compares it to the stored templates to see if there is a match!

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Program Memory (HDD/RAM)

Data Memory (RAM)

Template Storage Memory (HDD/Flash)

PC Microprocessor

USB Host Controller

PC

USB Port

AES2501x

USB RDK Figure 1-2 System Block Diagram

1.5

Integration Process

The process of integrating the AES2501B sensor into a product begins with the sensorrelated hardware design. This design process is started by reviewing the Reference Design Kit available from AuthenTec. Casing Design (Industrial Design) The external housing/casing design is usually the first item initiated by the integrator. This is due to the long lead times to produce the die for the casing. The casing design involves the correct mating of the top surfaces of the sensor. Swipe path must be smooth for a good experience for the end customer. The height of the AuthenTec sensor is reduced by the process of PCBA reflow. This change in height should not be overlooked during the design of the casing and mechanical mounting.

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SCHEMATIC and BoM This kit contains schematics and Bill of Materials for the USB interface design for the sensor. Printed Circuit Board (PCB) Layout To support the ESD immunity, the PCB layout is critical to passing the EMC-ESD compliance with the first pass of the PCB. Application Software While the hardware design process is underway, development of any application software required can be started by using a peripheral AuthenTec USB sensor module. This module will behave the same as the product being designed at the operating system level. BIOS preboot authentication development can also be performed using the USB module by using a PC-based BIOS development system. The USB module allows the sensor to be connected to a PC USB port and tested with the software before the integrated sensor hardware has been completed. Driver Certification AuthenTec supplies the certified driver required by the sensor. AuthenTec provides a DLL containing the API for all sensor-related functions. So the only software development that is needed is at the application level or BIOS level. The last step in the integration process is to test the final product design. Many different kinds of testing should be performed, including basic electrical and compliance testing, as well as biometric testing to verify that the casing design provides smooth swiping action and thus consistent results. Then that the fingerprint matching results meet specification.

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Resources AuthenTec has both hardware and software kits and documentation to assist developers in creating products using the AES2501B sensor. Some of these resources are listed in the sections below.

2.1

Reference Desig n Kit

AuthenTec provides a Reference Design Kit (RDK) that includes schematics and Bill of Materials (BOM) for the sensor interface. Production information is included in this kit as well, such as PCBA solder reflow guidelines, cleaning procedures, handling procedures and a manufacturing test program (Checksensor). Casing integration guidelines are also provided in this primer. A USB sensor module is also included in this kit. The USB module can be used to begin software development and hardware checkout before the actual product hardware has been designed, greatly reducing the time to develop a new product. DOC. NO.

DOCUMENT TITLE

PURPOSE

2234

EntréPad AES2501B Fingerprint Sensor Product Specification Handling And Testing Procedures For The AuthenTec Sensors How To Clean The AuthenTec Sensor

2248

Reflow Profile For AuthenTec Sensors

No number No number 2331 2313 No number

Schematic of Reference Design Bill of Material supporting schematic CheckSensor Production Test Program IEC61000-4-2 ESD Test Procedure ROHS Declaration

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AES2501B Primer

AES2501B electrical and design specifications Guidelines for handling and testing the sensor Guidelines for cleaning the sensor Guidelines for reflow solder processing Schematic for electrical design Parts list Verification of sensor in production test Support for ESD compliance tests Supporting documentation for RoHS compliance Summary document to support customer integration

3064 2158

Table 2-1 RDK Documentation

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2.2

Manuf acturers Integration Kit

AuthenTec provides a Manufacturers Integration Kit (MIK) that includes schematics and Bill of Materials (BOM) for the sensor interface. Production information is included in this kit as well, such as PCBA solder reflow guidelines, cleaning procedures, handling procedures and a manufacturing test program. DOC. NO.

DOCUMENT TITLE

PURPOSE

2234

EntréPad AES2501B Fingerprint Sensor Product Specification Handling And Testing Procedures For The AuthenTec Sensors How To Clean The AuthenTec Sensor

2248

Reflow Profile For AuthenTec Sensors

AES2501B electrical and design specifications Guidelines for handling and testing the sensor Guidelines for cleaning the sensor Guidelines for reflow solder processing USB.ORG compliance test report Verification of sensor in production test EMC compliance capability Support for ESD compliance tests Definition of product longevity Supporting documentation for RoHS compliance Summary document to support customer integration

3064 2158

no number 2313 3068 no number

USB Certification CheckSensor Production Test Program CE test report IEC61000-4-2 ESD Test Procedure Reliability Qualification Summary ROHS Declaration

3070

AES2501B Primer

2331

Table 2-2 MIK Contents

2.3

Software Development Kits

By providing Software Development Kits (SDK), AuthenTec supports any PC or Windows software development necessary to use the AES2501B in an application. A preboot authentication (PBA) software kit for BIOS development is also available. This kit should be used by integrators desiring to use fingerprint authentication to enable and disable a PC’s boot process, for added security.

2.3.1 Software Development Kit In the Software Development Kit (SDK), AuthenTec provides a Windows driver for the sensor and a DLL. The DLL contains an Application Programming Interface (API) that can be used to develop application software using the sensor. Full documentation of the DLL is also provided in the kit. The API contains functions for high level biometric functions, like enrolling and verifying fingerprints, as well as for lower level functions that capture

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fingerprint images, perform fingerprint matching, manage the encrypted template database, and so on. The Programmers Reference manual also incorporates an Installers’ Guide, which provides information to vendors of application software on how to install the AuthenTec Windows components (driver and DLL).

DOC. NO.

2060

No number

DOCUMENT TITLE

AuthenTec Windows Fingerprint Software Version X.Y for Microsoft Windows SDK Users Guide

PURPOSE

Programming Reference Manual for the AuthenTec API in Windows including installer guide Users’ guide for the SDK

Table 2-3 SDK Document Contents

2.3.2 Preboot Authenti cation (PBA) Kit A functional diagram of how preboot authentication works is shown in the figure below. In this model, fingerprint authentication is used to prevent the PC from booting up if the enrolled user is not present. As its name implies, preboot authentication occurs prior to the PC booting up (at the BIOS level), but enrollment of fingerprints and other management functions are performed at the operating system level for convenience. Fingerprint templates are stored on either the hard disk drive (HDD) or in system flash memory.

Figure 2-1 PBA Functional Diagram

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The PBA kit consists of three components: 1. The standard AuthenTec Windows DLL 2. A loadable binary executable that provides pre-boot sensor control, matching and user interface functions 3. A BIOS option ROM component that validates, loads and runs the loadable binary executables. The option ROM approach allows the PBA software to be implemented without any changes to the original BIOS. The option ROM component can also be provided in an entry point invocable form, but in this case some small changes to the original BIOS are required. The software in this kit is written as generically as possible so that it can be adapted to any manufacturer’s BIOS.

DOC. NO.

3044

2.3.3

DOCUMENT TITLE

PBA Integrator’s Guide

PURPOSE

Description of AuthenTec PBA Software and how to integrate it into a BIOS

Using Third-Party Matchers

The AuthenTec Windows software is designed to allow third-party matchers to be used. The AuthenTec API can supply the optimized, stacked image produced by the sensor control software to any matcher that can work with this type of image. The AuthenTec Preboot Authentication software is not currently designed to work with third-party matchers.

2.4

Industr ial and Mechanical Design

Information for designing an optimum housing for the sensor when it is used in a product can be found later in this document.

2.5

Signal Naming Convention

The signal and pin names used in this document are the same as the names that are referenced in AuthenTec’s Reference Design Kit. The symbols “*” and “#” used after a signal name, and the symbol “/” before a signal name, indicate that the signal is active low.

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3

Theory Of Operation The AES2501B pixel array is composed of 16 rows of 192 pixels (columns). The array is scanned sequentially by powering up 16 pixels in each column and then converting the analog values for each pixel to digital values. During fingerprint imaging, an RF signal is conducted via the Drive Ring on the surface of the sensor to the user’s finger. This signal is essential to the imaging process, so the sensor housing must be designed so that the Drive Ring is not covered up. The Drive Ring is represented by the Excitation Generator in the figure below. The signal that is generated by the Excitation Generator is conducted by the living layer of the skin in the finger. The living layer of the skin is high in saline content, which makes it a much better conductor than the dead, dry skin that forms the skin surface that we can see. The RF signal injected into the living layer forms an electric field that varies in strength depending on whether there is a fingerprint ridge or valley present.

Cross section of finger skin Live skin cell layer

Outer dead skin layer (dielectric) surface of the skin

Pixel antennae array Semiconductor substrate Excitation signal reference plane

Excitation Generator

Figure 3-1 Sensor Imaging Principle

Each pixel is connected to an RF sense-amplifier that detects the modulated electric field around the fingertip and amplifies and buffers it. Each pixel output is then converted into a digital level corresponding to the strength of the local field. A frame of the fingerprint image is scanned column by column. A column is scanned in ~32µs, and an entire frame of 192 columns is scanned in ~6.144ms. The AuthenTec driver automatically adjusts the sensor to obtain the best image and receives the image frame by frame. The individual frames are stored in a swipe buffer for further processing by the AuthenTec matcher software. The image stored in the swipe buffer is a stacked

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image like the one in the figure below, and has not been processed to analyze the individual slices together into a coherent fingerprint.

Figur e 3-2 Stacked Image Slices

The stacked image is processed by the AuthenTec software to extract information that can be used for matching fingerprints. This extracted information is called a “template”, and is much smaller in size than the original stacked image.

3.1

Sensor Data Types

In response to commands from a host processor, the sensor returns several fixed types of data, including such data types as register data and histogram data. The data types are defined in the Product Specification for the AES2501B, document #3064. The sensor will always return a complete data transaction in response to a command.

3.2

Senso r Operation In A System

The sensor system has several basic modes of operation in a system: • • • •

Finger Detect Mode Fingerprint Imaging Mode Scrolling Mode Remote Wakeup

These modes are explained below.

3.2.1 Fing er Detect Mode Before a fingerprint image can be captured, the sensor must first detect that a finger has been placed on the sensor. This operation is called the “finger detect mode”. The device drivers that support the AES2501B utilize the method of image based finger detection. The device driver will request the sensor to deliver the array scan data, then process this data and determine whether a finger has been placed on the sensor.

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3.2.2 Fingerpr int Imaging Mode The Fingerprint Imaging Mode is the mode used when the sensor is capturing a fingerprint image for biometric purposes. When a fingerprint image has been requested, the sensor first operates in Finger Detect Mode until a finger swipe is started by the user or the operation times out. If a finger is detected, the sensor switches to Imaging Mode to capture a stacked image and send it to the host processor. When the finger is removed from the sensor (or the imaging process times out), imaging mode is ended and processing of the image begins in software. All of these mode changes are automatically performed by the AuthenTec driver and DLL, and the system designer need not be concerned with the details of how this is performed.

3.2.3 Scrollin g Mode When the sensor is used as a scrolling device, the sequence is different. In this case, a repeating sequence of images is sent by the sensor to the host computer. Software evaluates this stream of images to determine in which direction the finger is moving, and by how much. The sensitivity can be adjusted to provide for personalization, at the price of power consumption, or lower performance with improved power consumption for less demanding applications.

3.3

Fault Detection And Correction

The AES2501B has several built-in mechanisms for detecting fault conditions and recovering from them. Usually, these fault conditions occur as a result of an ESD event. The most important fault detection mechanism inside the sensor is an overcurrent (OVC) detection circuit that uses an external sense resistor to measure the current in the digital portion of the sensor. This circuit is used to detect latchup events that occur as a result of ESD or power supply inversion. If the OVC detection circuit is triggered, the AES2501B will turn off its own VDD power and then turn it back on, using an external switching device to control the power rail. This power cycling will clear the latchup condition and cause a USB re-enumeration. The OVC detection circuit is described more fully in a later section of this document. There are also other built-in fault detection mechanisms that may be used if needed. These mechanisms are enabled and disabled through software. If they are enabled, the sensor will automatically perform a re-enumeration and a master reset in response to an error condition. The AuthenTec driver will implement these features if they are required. As part of each AuthenTec sensor qualification, all compliance tests are run to validate the recovery of anomalous events.

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4

Electrical Design This section describes the design of the various circuit elements that are needed around the sensor.

4.1

Power Suppl y Design

The VDD supply for the sensor must meet certain requirements for the sensor to work properly and reliably. The following sections address these requirements.

4.1.1 Supply Voltages And Currents The AES2501B sensor will work with power supply voltages from 3.0V to 3.6V, and the supply voltage should never exceed 4.3V. Since USB bus power is often 4.5 to 5.5V, this voltage would need to be regulated down to the sensor nominal operating voltage of 3.3V. If a voltage regulator is used, it should be specified to supply at least the worst-case imaging mode current ~70mA. The worst-case currents occur during imaging mode. During scrolling mode, the sensor current will be 25mA (typical). The USB specification requires that a low power device such as the sensor use a power supply current of 100mA or less, which is more than enough for the sensor.

4.1.2 Supply Voltage Noise Requirements A critical power supply requirement for the sensor is that peak-to-peak ripple (noise) on the power supply must not exceed 100mV. The ripple should be carefully checked on the actual PC board for the product to ensure that this requirement is met. The worst-case ripple occurs when the USB D+ signal is active. The figure below shows how this measurement can be performed with an oscilloscope, and is an example of good power supply ripple.

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Figur e 4-1 VDD Ripple Measurement

4.1.3 Supply Voltage Rise Time Requirements The VDD supply for the sensor should be designed to rise monotonically from 0V to the VDD voltage. VDD characteristics like those shown in the figure below must be avoided. In this kind of situation, reset is correctly released (exceeds 2/3 * VDD, or 2.2V) after VDD exceeds 3.0V, but then VDD falls back below 3.0V again, causing reset to have been released prematurely. This can result in incorrect sensor operation.

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Voltage VDD 3.0V

RESET

2/3*VDD

Time Figur e 4-2 Improper VDD Characteristics

VDD should rise to its final value in significantly less time than that taken by the reset to reach 2/3 * VDD (2.2V for a 3.3V nominal sensor voltage).

4.1.4 Power Control Desig n The sensor power must be controlled with hardware so that the sensor can turn its own power on and off under the control of its overcurrent detection circuit. This power control is used to recover from latchup events in the sensor caused by Electrostatic Discharges (ESD). When an electrostatic discharge occurs, it is possible for the sensor, like all other CMOS integrated circuits, to go into latchup. CMOS circuits inherently contain four-layer devices that can behave like SCRs. This typically occurs when the VDD power supply is momentarily biased at a lower voltage than the sensor ground. This power supply inversion can occur during an ESD event, or due to some other fault in the power supply. When latchup occurs, the sensor will draw a large amount of current and can also become uncomfortably warm. The sensor has a built-in overcurrent detection circuit that prevents this condition from continuing by switching off the power to the sensor momentarily when it occurs. Additionally, sensor supply current limiting is required for safety in USB applications. USB ports in PCs can sometimes supply very large amounts of current into a short circuit. In some PCs, this current can reach 5A or more. This can result in a dangerous situation if the sensor becomes physically damaged. To prevent safety problems, the current to the sensor should be limited to ~250mA. The goal is for the sensor to remain below 60C temperature. The voltage regulators which are not specifically designed to be a current limiter are not reliable current limiters and cannot be used for this purpose. Using a devices which interrupts that power and restores it would be advisable, as opposed to current foldback.

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For the above reasons, it is very important to supply a means for the sensor power to be turned on and off and to limit the current to the sensor. The block diagram below shows the method recommended for this. A current-limited P-Channel MOSFET switch is used on the high side of the sensor (VDD) to control the sensor current. The Analogic AAT4610A is a current-limited MOSFET whose current limit is set to trip at typical 250mA by the 40.2Kohm resistor. If the sensor is physically damaged and draws excessive current, the AAT4610A will prevent this from reaching dangerous levels. The AAT4610A is turned on and off by the sensor itself by using the signal from pin D9 (OVC_DET). The sensor’s built-in overcurrent detection circuit is isolated from the rest of the sensor. The pad D10 (OVC_VDDA) and D8 (OVC_VDD) supply the power to this isolated circuit. The 2ohm sense resistor is used to measure the current entering the digital portion of the sensor. If the voltage drop across the sense resistor exceeds the threshold for a sufficiently long time, the OVC_DET signal will go high for a set period of time, turning off power to the sensor. After the time period has elapsed, the OVC_DET signal will go low again, automatically turning sensor power back on. The specifications for the sensor’s OVC_DET circuit are shown in the table below. P ARAMETER

Sense resistor threshold voltage Overcurrent time required to trip OVC_DET Time OVC_DET signal is high after tripping

MINIMUM

TYPICAL

M AXIMUM

UNITS

40 17.1

70 25.7

100 51.4

mV ms

119.4

179.1

358.2

ms

Table 4-1 OVC_DET Specifications

All parts of this circuit design are critical for proper operation of the sensor and cannot be omitted. The sense resistor value is critical and is specified as 2 ohms ±1%. D8: OVC_VDD

VDD2

AAT4610A 3.3V_REG

5 In

Out

4 #On

1

D10: OVC_VDDA

Sense Resistor 2 ohm, 1%

Set 3 2

39K

D11: OVC_SENSE

AES2501x

B3: VDD A8: VDD

D9: OVC_DET*

Figure 4-3 Power Control Design (VDD)

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The analog power (VDDA) for the sensor is controlled separately, using the circuit shown in the block diagram below. The analog power supply current is not monitored by the sense resistor. This current cannot be monitored because it varies widely between imaging mode and other modes, unlike the digital (VDD) current. However, the sensor uses the Pchannel MOSFET Q1 to control VDDA power, and only turns this power on when the sensor is capturing a fingerprint image. This prevents analog array latchups from occurring during ESD events. The MOSFET Q1 must be selected to have low on-state resistance (Rdson) to avoid having a large voltage drop while the sensor is imaging. The MOSFET threshold voltage must also be selected for 3.0V operation, so that the MOSFET will be fully turned on at the minimum gate voltage of –2.7V.

VDD2

C3: VDDA C12: VDDA

Q1

AES2501x C10: VDDA_ON*

Figure 4-4 Power Control Design (VDDA)

The designer should test the sensor power on the actual PC board to ensure that the following conditions are met: 1. The USB power (regulated down from 5.0V to 3.3V, i.e., 3.3V_REG) turn-on is monotonic and reaches full VDD within the specified time with respect to reset and the oscillator turn-on. 2. When the sensor VDD is turned off by the AAT4610A, it falls to a value less than 0.5V within a few milliseconds. If VDD never falls to less than 0.5V, this probably indicates that one or more sensor inputs is not being turned off when VDD is turned off. This might happen, for example, if the serial flash connected to the sensor is supplied with power from 3.3V_REG rather than from VDD2. On the other hand, if the turn-off time is too long, a resistor with a large value may be placed in parallel with the sensor in order to bleed off stored charge more quickly.

4.2

Clock Circuit Design

The AES2501B can use either a crystal oscillator or resonator for a clock source, or an externally driven clock. The following sections discuss the requirements for each of these options. There are several possible clock frequencies that may be used, and the frequency selected should be specified by connecting the sensor pins B1, B6 and C5 as shown in the table below.

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CLKSEL2

CLKSEL1

CLKSEL0

CRYSTAL /RESONATOR OR

PIN B1

PIN B6

PIN C5

CLOCK FREQUENCY R ANGES

0 0 0 0 1 1 1 1

0 0 1 1 0 0 1 1

0 1 0 1 0 1 0 1

6 MHz Reserved 12MHz 18MHz 24MHz Reserved Reserved 48MHz (PLL Bypass mode, clock only)

Table 4-2 Clock Frequency Settings

In PLL Bypass mode, the sensor must be driven with a 48MHz clock through the SYS_CLK pin.

4.2.1 Crystal Circui t Desig n The sensor is designed to use a one-pin oscillator, which means that a crystal or resonator is connected to the sensor through the single pin A11 (SYS_CLK). Board capacitance is critical in this design, because it greatly affects the crystal or resonator start-up time. Careful analysis of the oscillator start-up time using the actual PC board should be performed to ensure that the oscillator start-up time requirements are met over the range of board and capacitor variability. The schematic below shows the pin connections related to using a crystal or resonator as the clock source.

A11: SYS_CLK

C 10pF

Y 6/12MHz

R 47K

AES1610

4.2.1.1 Crystal Oscillato r Start-up Time Requirements

When a crystal or resonator is used as the sensor clock, the clock ramp time is dependent upon the start-up time of the crystal or resonator. The load capacitance on SYS_CLK and

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the characteristics of the crystal or resonator will determine this start-up time. The oscillator start-up time must be 9ms or less, or the digital PLL in the sensor may lock on an incorrect frequency. Some crystal and resonators may have too long of a start-up time to be used in this application, so the crystal should not be selected solely based on cost. The start-up time of the oscillator should be verified on the actual circuit board using a low capacitance (1pF or less) oscilloscope probe to prevent excessive loading on the SYS_CLK pin. AuthenTec’s reference design, which includes a capacitor of 10pF, has a worst-case startup time of 9ms. RESET* can be released 9.01ms after VDD reaches 3.0V. VDD (3.3V)

3.0V

SYS_CLK

Clock stable in < 9ms

RESET

Reset at > 9ms Figur e 4-5 Reset Time With Crystal Or Resonator

The oscillator start-up time should be measured on the actual circuit board using a low capacitance oscilloscope probe. Normal oscilloscope probes may have 10 – 15pF of capacitance, which will significantly change the loading on the oscillator and change the start-up time. An example of a start-up time measurement is shown in the figure below. The start-up time is measured from when the oscillator pin rises to VDD/2 to when the oscillation frequency has stabilized at its design value and maximum amplitude.

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Start-u Time ~1.5ms

Figure 4-6 Measuring Oscillator Start-up Time

4.2.1.2 Crystal Osci llator Or Resonator Specificatio ns

The crystal or resonator used with the sensor must meet the requirements shown in the table below. The crystal must be of the series resonant type. Any crystal or resonator that meets the specifications can be used. P ARAMETER

MINIMUM

M AXIMUM

UNITS

Frequency Frequency CLK_SEL=1 Frequency CLK_SEL=0 Shunt Capacitance (Co) Series Capacitance Inductance ESR Q

Freq.(nominal) – 0.25% 11.97

Freq.(nominal) + 0.25% 12.03

MHz

5.985

6.015

MHz

1 2.0 69 25 130,000

2 2.5 78 43 210,000

pF fF MH Ohms -

Table 4-3 Crystal/Resonato r Specifications

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4.2.2 External Clock Circuit Desig n It is also possible to drive the sensor clock with an external clock source, although this arrangement is not commonly used. The connections when using an externally driven clock are shown in the figure below. The external clock is connected to pin A11 (SYS_CLK) of the sensor. The clock must be a gated clock, and must be turned off when the OVC_DET signal has turned the sensor power off. This is because the sensor can be powered up through the SYS_CLK pin, which will prevent any latchup conditions from being cleared if the clock continues to run with the sensor power turned off. OVC_DET

B2: SYS_CLK

CLK 6/12MHz

AES1610

Figure 4-7 External Clock Using SYS_CLK Connection

Another very important point to note is that it may be impossible to meet the USB specification suspend current requirements when using an external clock . Pin B7 from the sensor would need to be used to disable the clock. Without using the pin B7 as as signal to shutdown the clock, the sensor power supply current would be out of specification for the suspend mode.

4.2.2.1 Externally-Driven Clock Start-up Time Requirement s

The external clock should be held in the low state until VDD reaches at least 3.0V. This prevents powering up the sensor through the input protection network on the SYS_CLK pin. SYS_CLK can be applied any time after VDD reaches 3.0V. If using the internal PLL, time is required for it to stabilize before operating the sensor. The PLL lock time is 1ms worst case. The lock time starts from either clock starting or reset being released, whichever comes last. The external clock should be stable and meet the required drive specifications within 1.5ms of VDD reaching 3.0V, and reset may then, for example, be released 2.5ms after power on. The clock may be active or inactive when reset is applied or released. The 0.047µF reset capacitor recommended for use with an external clock will release reset after ~2.5ms.

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RESET* should be released at least 10 ns after VDD reaches 3.0V. RESET* can be released before or after the external clock has started, however the 1ms PLL lock time must always be observed before starting sensor operations. The figure below shows an example of the start-up time for an externally driven clock, when using the SYS_CLK pin. Note that reset could also occur 10ns after VDD reaches 3.0V without affecting sensor operation. VDD

3.0V

SYS_CLK

Clock stable in 1.5ms

RESET*

Reset at 2.5ms Figure 4-8 Reset Timing Example With Externall y-Driven Clock On SYS_CLK Pin

4.2.2.2 Externally-Driven Clock Specificatio ns And Noise

When an externally driven clock source is used, the figure and table below give the specifications required for the clock source:

Figure 4-9 External Clock Specifications

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P ARAMETER

MINIMUM

M AXIMUM

UNITS

Frequency Frequency CLK_SEL[2:0]=010 Frequency CLK_SEL[2:0]=000 Jitter Tr Tf Thigh Tlow

Freq.(nominal) – 0.25% 11.97

Freq.(nominal) + 0.25% 12.03

MHz

5.985

6.015

MHz ns

45%*[Tperiod] 45%*[Tperiod]

2 10% of Tperiod 10% of Tperiod 55%*[Tperiod] 55%*[Tperiod]

Table 4-4 External Clock Specificatio ns

4.3

Reset Circu it Desig n

The sensor must be held in reset until the VDD power supply has reached at least 3.0V. In USB designs, reset is always performed by a capacitor connected to the RESET* pin of the sensor. A ceramic capacitor (C) is connected to RESET* (pin A5). This capacitor is connected to VDD through a 57.1Kohm ( ± 15%) resistor that is inside the sensor. When a crystal oscillator is used, the value of the reset capacitor should be 0.22µF, assuming that the crystal start-up time meets the requirements specified above. This value will guarantee that reset is not released until the oscillator has started up. When an externally driven clock is used, the value of the reset capacitor should be 0.047µF. The time for reset to be released when using a capacitor can easily be calculated by multiplying the capacitor value by the value of the reset resistor inside the sensor (57.1Kohms). For example, the nominal time to release reset for a 0.22µF capacitor is: 0.22x10-6 X 57.1x103 = 12.5ms

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AES2501x A5: RESET*

C

Figure 4-10 Reset Circui t

4.3.1 Reset Timin g Consid erations Reset should be designed so that it is released (reaches a voltage of 2/3 * VDD) at least 10ns after VDD reaches 3.0V. However, this timing may be modified depending on what type of clock or oscillator is used (see sections above on clock design). The minimum timing should be as shown in the figure below, which could be used in the case of an external clock. For a crystal oscillator, the timing should be as shown in the section Crystal Circuit Design. Voltage

VDD

RESET

3.0V 2/3*VDD

Time >10ns

Figur e 4-11 Reset Timing And VDD

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4.4

USB Interface Desig n

The USB interface of the sensor is shown in the block diagram below. The present design of the AES2501B does not connected the ENUM pin (C9) of the sensor. For example, an ESD event may upset the sensor and cause the OVC circuit to trigger. Once the OVC circuit is triggered, the OVC circuit will cycle the power. The sensor power rail drops as power is cycled. This power cycle pulls the USB D+ line low and back high, which will cause the USB host controller to re-enumerate the sensor. The 24 ohm resistors in the D+ and D- lines are used to control the rise and fall times of the USB signals. The values of these resistors may need to be adjusted in some cases in order to maintain the rise and fall characteristics within the USB specification limits. C9: ENUM

VDD

1.5K AES2501x

24

USB D+

B9: DPLUS

24

USB D-

B10: DMINUS

Figure 4-12 USB Connections

4.4.1 Interface Volt ages The signals on the USB D+ and D- lines (and other inputs) to the sensor should meet the VIH and VIL requirements shown in the table below to ensure that logic levels will be recognized by the sensor. SYMBOL

VIH VIL

DESCRIPTION

High Level Input Voltage Low Level Input Voltage

MIN

70% VDD 0

M AX

VDD 30% VDD

Table 4-5 Interface Voltages

4.5

Charge Pump Filter

The sensor requires an external charge pump filter for the analog PLL to operate correctly. This filter is connected as shown in the block diagram below. The component values in this circuit should never be changed

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A10: PLL_FILTER

10pF

1K

1000pF

AES2501x

Figure 4-13 Charge Pump Filter

4.6

Finger Ring Circuit

In order to image a fingerprint, the sensor must generate an AC signal on the finger ring which is on the surface of the sensor. The circuit for this finger ring signal is simple, including a resistor and an SR05 for ESD protection. The value of the resistor (47ohms) was selected empirically through extensive ESD testing, and has been found to give the best ESD protection. This circuit is shown in the figure below.

4.6.1 TVS Characterist ics and Clamping Voltage The capacitance of the TVS, the PSR05 or the SR05, should not be greater than 12pF line-line or line-ground. The clamping voltage should not be greater than 10VDC when using 8/20uS disturbance testing and current of 1 ampere. WARNING: too much capacitance on this node may cause operational issues with transition to standby on platforms. If there is concern, consult AuthenTec Applications.

4.6.2 Chassis Ground Connecti on The grounding of this circuit is extremely important for good ESD protection (see PC Layout Considerations in a later section of this document).

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A12: DRIVE_RING

3.3V REG

IO2

PWR

SR05

47ohms

AES2501x

IO1 GND

USB Shield

A4: FDRV

Figure 4-14 Finger Ring Circuit

5

PCB Layout Considerations When a PC board is designed using the sensor, there are some precautions that should be taken in part placement and routing to ensure low EMI generation and good ESD performance. The sections below describe the best PC board layout practices for the sensor.

5.1

Decoup ling Capacitor s

The decoupling capacitors for the sensor should be placed as close to the sensor pins to which they are connected as possible. Decoupling capacitors should never be placed far away from the sensor pins. The drawing below illustrates proper placement of a decoupling capacitor C5 to the power pads of the sensor. C5 is on one side of the board and the sensor is on the opposite side.

Figure 5-1 Decoupling Capacitor Placement

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5.2

Crystal Placement

The crystal or resonator should also be placed as close to the sensor pins as possible. The routing lines for the crystal should not have right angle bends, in order to reduce EMI spray. The crystal’s connecting traces should also be surrounded by ground plane. The drawing below shows an example of good crystal placement.

Sensor Pads

Crystal

Figure 5-2 Crystal Placement

5.3

ESD Design

The placement of the ESD protection device (TVS) is very critical. This part must be placed as close as possible to the sensor pins to which it is connected, and must be directly connected to the ground plane. It is best to make the ground plane connection with two or more vias. This device should never have long traces connected to it or a long path

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to ground. Since ESD events occur at gigahertz frequencies, even short traces can add significant inductance to the circuit and cause the device to provide less ESD protection.

5.3.1 TVS Device Selecti on If it is desired that a different ESD protection device than the one recommended in the AuthenTec reference design be used, it is very important that it first be thoroughly tested. There are many replacement devices that are commonly used, such as Zener diodes, which do not provide adequate protection for the sensor. Use of this type of device can result in field reliability failures. Contact AuthenTec for recommendations when considering alternative devices for ESD protection. Presently only Protek with their PSR05 and Semtech with the SR05 are qualified devices.

5.3.2 TVS Characterist ics and Clamping Voltage The capacitance of the TVS, the PSR05 or the SR05, should not be greater than 12pF line-line or line-ground. The clamping voltage should not be greater than 10VDC when using 8/20uS disturbance testing and current of 1 ampere. WARNING: too much capacitance on this node may cause operational issues with transition to standby on platforms. If there is concern, consult AuthenTec Applications. Typical parameters should be similar to the device specifications below.

5.3.3 TVS PCBA Placement The figure below illustrates good SR05 placement and connection to the ground plane.

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Sensor Pads

SR05

Figur e 5-3 SR05 Placement (Ground Plane Not Shown For Clarity)

5.3.4 Casing Crevice ESD When a nonconductive housing is used around the sensor, there may be a gap for ESD discharges to reach the PCBA surface around the sensor. The PCBA can be constructed to address this problem. There is an explanation of this implementation below. Another method to provide immunity to the Casing Crevice ESD is for the backside of the casing to be sprayed with conductive coating to allow the ESD to conduct to that casing backside surface. There is no exposed leadframe on the AES2501B. These design methods are only needed with nonconductive sensor casings, since conductive casings will absorb ESD discharges around the sides of the sensor.

5.3.4.1 PCBA Sensor Grou nd Ring

The ground plane of the PC board should be extended under the edge of the sensor on the surface of the board, as shown in the figure below. Electrostatic discharges can sometimes jump around the edges of the sensor and could hit the sensor balls underneath or other traces on the PCBA. The balls are the sensor pins and are only rated to withstand ESD voltages found in assembly operations, not in field use. This type of discharge can damage the sensor, if not prevented by the extension of the ground plane underneath the sensor edge. Note that no ground plane is allowed underneath the sensor within the ball grid array itself. The minimum spacing between the ground plane and the sensor ball pads is 6 mils (0.1524mm). In addition, if PC board traces must be placed on the surface of the board near the sensor, they should be covered with labeling silkscreen paint to prevent ESD discharges to the

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traces. Discharges to the PC board traces can upset the circuitry or damage the sensor, which can cause an ESD immunity test to fail. The white boundary is the outline of the sensor. The yellow area is the exposed copper of the top layer of the PCBA. Notice that the exposed copper goes under the lip of the sensor edge.

Figure 5-4 Extensio n Of Ground Plane Underneath Sensor Edges

5.4

Interface sig nals

The USB D+ and D- signals should be routed to their destinations without right angle bends to reduce EMI spray. These signals should also be routed with the traces parallel to each other as much as possible and surrounded by ground plane to further reduce EMI generation.

5.5

Test Point

In addition to the normal circuitry on the PC board, designers may wish to incorporate test points for debugging purposes. There are two signals that may be useful in debugging. One is the USB transceiver output enable (OE#) signal pin (B8). The second is the SUSPEND output, signal pin (B7), which is active when the sensor is in the SUSPEND state. It is best to place a test pad for this signal on the opposite side of the board from the

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sensor, and located at some distance away from the sensor, to prevent it from being affected by ESD discharges. An example of the placement of these test pads is shown below.

Test Pad (OE#)

Sensor Pads

Figure 5-5 Test Pad For USB OE# Signal

6

Grounding And Shielding In order to obtain good results in ESD testing of the sensor, proper grounding and shielding design is required. When a sensor is integrated inside a product, the USB signal ground should not be completely relied upon to connect the sensor board to ground. The USB cable ground signal is not necessarily a direct path to chassis ground, and moreover, it is often a long, thin and highly inductive line. These characteristics make it a very weak ground at ESD event frequencies. The best grounding practice is to use a screw or bolt to directly connect the sensor board to chassis ground. This single design factor can dramatically improve ESD performance, all other things being equal. When the sensor is incorporated in a peripheral module, connecting the sensor board to chassis ground is usually not possible. In this case, one or more ferrite beads should be added to the USB cable to help suppress EMI transients that are coupled into the USB cable or shield by ESD events. The AuthenTec USB sensor module in the reference design kit includes this feature. In addition to improving the sensor module ESD

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performance, the ferrite bead also helps to prevent EMI pulses from upsetting the PC USB port. The USB specification requires that USB cables have a shield. However, when USB devices are integrated into a PC or other hardware platform, this requirement is frequently ignored. This may be due to the difficulty in making flat cables with a shield around them. In any case, this lack of shielding can have a very deleterious effect on ESD test results. One indicator of this problem is when ESD discharges to the product housing around the sensor, or even in locations far away from the sensor, cause the sensor to re-enumerate or stop working. An unshielded USB cable is essentially a long antenna that can receive the EMI pulses from ESD events very efficiently. This coupled EMI can upset the USB port connected to the sensor, or even the CPU. To avoid this kind of problem, be careful to shield the USB cable, even if it is inside the equipment. The cable shield should be connected directly to chassis ground if the board ground has not been connected to chassis ground.

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7

Industrial Design When the AuthenTec AES2501x series sensors are incorporated into a consumer product, the casing of the product must be designed so that the sensor can be used easily, comfortably, and reliably. The sensor is designed for a finger to be swiped across its sensing surface in order to capture a fingerprint, or for a finger to be moved around on its surface when using it as a navigation device. The housing around the sensor must be designed so that it does not obstruct the movement of the finger; otherwise the biometric or navigation performance of the sensor may be compromised. The False Rejection Rate (FRR) may increase if a finger cannot be swiped properly across the sensor surface, or the ability to navigate into certain areas may be obstructed. The success of the biometric and navigation functions can be greatly enhanced by an appealing, functional and intuitive design. Consumer electronic devices are designed with several factors in mind, including aesthetic form, ergonomic function, and product brand identity. Likewise, the industrial design for the sensor should include all of these factors. This means that the location of the sensor on the product and the design of the areas around the sensor must be carefully considered. The fingerprint sensor casing design is as important as cell phone keypad design or computer touchpad layout in creating a beautiful and functional product. This section explains the guidelines for an optimum industrial design for a product using the sensor. The intended audience for this document includes industrial and mechanical designers.

7.1

Design Consideration s Care must be taken to ensure proper clearance of the housing/casing around the sensor to provide good contact between the finger and the sensor surface during the process of sliding a finger across the sensor. AuthenTec has tested various housing designs to develop guidelines to achieve the best contact between the finger and the sensor. The final image quality has many determinants including swipe speed, skin types, rotation, and twisting of the finger during sliding, ensuring maximum planar contact between the finger. The key part of all of these factors is that contact with the sensor is necessary to obtain good quality images.

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7.2

Finger in con tact with surf ace of sensor When deciding on the housing design for the sensor, the most important factor is to keep the finger surface in direct contact with the sensing array during the entire "swipe" of the finger. This can be best accomplished by making the sensor housing leading up to the contact area of the sensor surface planar with the sensor surface. The active sensor surface should not project above or be recessed below the surface of the housing. There should also be ample room in the groove that guides the finger during its swiping action so that the entire top joint of the finger can slide along the surface of the sensor without difficulty.

7.3

Top surf ace of casing mates flus h with sensor wing s The sensor has areas that contain bond wires at each end (“wings”, see diagram below) that protrude above the active sensor area. These areas can present a rough or sharp feel to the user’s finger if the housing is not designed to conceal these edges. The housing should be designed with a smoothly sloping surface that is planar with the sensor wings on the sides to prevent an uncomfortable sensation when sliding the finger along the surface of the sensor. Sensor Wings (side view)

Figur e 7-1 Sensor Wings

7.4

Mating alig nment shou ld not rely on the sensor itself

Another important design factor is that the housing should not press down on the sensor too hard. If too much pressure is applied to the body of the sensor, it is possible to fracture the sensor package or chip, causing the sensor to fail. For this reason, it is best if the housing does not cover the sensor package, since this will prevent pressure from being applied to it. To assist in the assembly process, studs or guides should be implemented on the bottom of the housing piece that covers the sensor to ensure that the housing can be installed on top of the sensor without accidentally applying pressure to the wings. These studs or guides should be designed to fit into holes or slots on the sensor PC board. In some applications, it may be necessary to seal the area around the sensor in order to prevent liquids or dirt from intruding into the housing. A rubber gasket may be used for this purpose.

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In practice, it may be difficult to achieve the ideal housing design due to product form factor limitations. However, efforts should be made to approach these guidelines as closely as possible. To summarize the important design points: 1. The housing design should maximize planar contact between the sensor surface and finger. The finger groove ideally should have a 0º angle, but should not exceed a 10º angle. The finger groove should be long enough to accommodate the entire top joint of the user’s finger. 2. Sensor surface should not project above housing or be recessed below housing. 3. The top surface of the housing should flow into the top surfaces of the sides of the sensor, so that no sharp edges can be felt. 4. The housing should not apply excessive pressure to the sensor body. The best housing design does not cover the sensor body. Studs or guides should be used to ensure proper assembly. Clearance between the sensor and the housing for designs that do not have gaskets around the sensor should be a minimum of 0.1mm. 5. A gasket made from a soft material may be used to seal the opening around the sensor.

7.5

Design Specifi cations This section gives detailed specifications for designing the best sensor housing.

7.5.1 Entry And Exit Angles The angles of the housing that are along the path that a finger slides along the surface (finger groove) should be designed to be 0º if possible. As a maximum, these angles should be no more than 10º. This is shown in the figure below.

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Direction of finger movement

Acceptab le angle < 10 d egrees

Optimum finger groove angle 0 degrees

Sensor surface

Finger Groove

Sensor Wing

Housing planar with sensor wings

Housing

Housing slightly beveled here

PC Board

Figure 7-2 Housing Design Specifications

The ends of the finger groove should blend smoothly into the surface of the product housing, and should never be terminated with a vertical step in the housing.

Correct: Finger groove blends with housing surface

Sensor Wing

Figur e 7-3 Correct Fing er Groove Design (Side View)

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Incorrect: Finger groove ends in vertical step

Sensor W ing

Figure 7-4 Incorrect Finger Groove Design (Side View)

The finger groove (or finger sliding area) should be designed to be planar with the top surface of the sensor. The sensor surface should not project above the finger groove area of the housing, nor should it be recessed below the finger groove area, as shown below.

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Correct: Finger groove planar wit h sensor surf ace

Sensor Wing Sensor Surface

Incorrect : Finger groov e higher than sensor surf ace

Incorrect : Finger groov e lower than sensor surface

Figure 7-5 Finger Groove (Side View)

7.5.2 Extent Of Finger Groove Most housing designs will have a groove (valley) to guide the user’s finger when sliding it along the sensor surface. This groove must be made long enough that the sensor can capture the entire fingertip without obstruction. Ideally, the groove or available sliding area at the top side of the sensor should be at least as long as the top joint of a finger, as shown in the figure below.

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Finger groove extent = length from first knuckle to end of finger

Finger Groove

Figur e 7-6 Finger Groove Extent

7.5.3 Design For Biometric Appli cations For applications in which the sensor is only used as a biometric identification device, the finger groove can be recessed below the housing surface. The figure below shows one way to design the finger groove that embodies this principle. This type of design is best for achieving repeatable finger swiping during authentication. Note that the finger groove is also long enough to accommodate the top joint of a finger.

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Figure 7-7 Optimal Finger Groove Design

Figure 7-8 Optimal Flush Mating w ith Casing and Taper to Sensor Wings Design

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In products with small surface areas, like tablet PCs, the finger groove area can be shortened by using design as shown in the example below. Note that the ends of the finger groove blend smoothly with the rest of the housing surface, without any vertical steps or other obstructions.

Figure 7-9 Shortened Finger Groove

7.5.4 Design For Navigation and Biometric Appli cations For applications in which the sensor is used as a navigation device, a design that allows the finger to move easily in any direction is preferable. One way to do this is to make the housing around the sensor completely flat and use small bumps to guide the finger, as shown in the figure below. The small bumps at the four corners of the sensor provide tactile guidance when sliding the finger.

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Figure 7-10 Planar Housing Design With Guide Bumps

7.5.5 Sensor To Housing Clearance It is very important to avoid applying pressure to the sensor with the product housing during assembly operations. For this reason, the housing must not be designed to have too tight a fit to the sensor. A minimum clearance between the sensor and housing of 0.1mm is recommended for designs that do not use a gasket around the sensor.

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7.5.6 Sensor Wing Desig n The housing should be designed so that the sensor wings are not covered up, and the housing is planar with the tops of the wings. A gently sloping angle from the top of the wings to the rest of the housing will help to ensure that the housing does not have a rough feeling when sliding a finger. It is also acceptable to make the top of the housing flat in this area rather than beveled, but a beveled area improves the feel of the sensor when sliding a finger. The figure below illustrates the best design for the wing area.

Housing planar with top of sensor wing Housing slightly beveled here

Figure 7-11 Housing Beveled Around Sensor Wings

Sensor Surface

Housing beveled smoothly around sensor wings

Housing

Sensor Wing

Figur e 7-12 Housin g Bevel (Side View)

This beveled design can be combined with guide bumps for added tactile guidance for navigation, as shown below. This type of design can be used for both biometric authentication and navigation applications.

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Beveled area around sensor wings

Guide Bumps

Figure 7-13 Beveled Wing Areas Combined With Guide Bumps

7.5.7 PCB to Housin g Guide for Mating Ali gnment In order to further protect the sensor package from pressure, as well as to ensure a uniform appearance of the sensor when mated to the housing, the part of the housing that contacts the sensor should be designed to have guides or studs on the bottom. These guides should fit into holes or grooves in the sensor PC board, as shown in the figure below. The design tolerance of these guides should be less than 0.1mm. This tolerance will correspond to the minimal clearance of the sensor to casing.

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Sensor Housing

Guide Stud Sensor PC Board Hole

Figure 7-14 Assembly Guides For Sensor Housin g

The sensor itself should never be used as a mechanical alignment guide to the housing opening. Subassemblies such as the PC board on which the sensor is mounted should not be used as alignment guides unless the subassembly has construction and alignment tolerances of less than 0.1mm, so that the housing opening will never touch the sensor edge during assembly. Perpendicular mating should always be used for subassemblies containing the sensor. Sensor assemblies that slide horizontally or that rotate vertically or horizontally into position create the possibility of damaging the sensor. 7.5.8 Gaskets In some applications, it may be necessary to use a gasket around the sensor in order to prevent liquids or dirt from entering the housing or coming into contact with the PC board. For example, if chemicals or liquids come into contact with the PC board, they may cause a short circuit. Gaskets can be made from soft rubber or other materials of this type. The gasket should be designed to be conformal with the sides of the sensor, including the sensor wing areas. The gasket may extend outward from the sides of the sensor to provide an area for the housing to seal against the gasket. The figure below shows how the gasket surrounds the sensor to prevent foreign materials from entering the housing.

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Sensor surface

Gasket

Figure 7-15 Gasket Design

An example of an actual gasket design is shown below. Note how the gasket material follows the contours of the sensor surface and extends outward from the sensor.

Figur e 7-16 Gasket Example

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8

Design Checklists The following checklists are provided to assist designers in making sure that all of the basic requirements for design with the sensor have been met. 

8.1

General Electri cal Desig n Checkli st  







8.2

Sensor power supply voltage is regulated in the range 3.0 – 3.6V P-Channel current-limited MOSFET or equivalent device used to control sensor VDD shall have a current trip limit of no greater than 400mA for 60C maximum thermal limit. Low RdsON P-Channel MOSFET used to control sensor VDDA, less than -0.2 ohms at 2.7Vgs. Design for power supply ripple (noise) to be less than 100mV peak-to-peak while D+ is active (sensor is imaging). Component substitutions should be the electrical equivalent of the devices they replace.

ESD and General PCBA Layou t Desig n Checkli st 









Components are placed and routed in order of priority for minimized trace lengths: FRNG, FDRV, clk, A10, DMINUS, DPLUS, VDD3.3, VDDA, all others. R5 should be placed between U3 and U4, with R5 (47 ohm) across pins 2-3 of the TVS TVS device placed as close as possible to sensor pins and connected with a wide trace to the sensor pins TVS pin 1 (GND) musts be 0.5mm minimum trace width and connect to chassis ground or USB shield. For all non-conductive casing installations - PC Board ground plane ring is around and extended under the edges of the sensor. All traces must escape beneath the sensor package outline to allow proper ground plane ring placement. The ground ring must be 0.15mm beneath the package outline and extend outward in all directions for 0.35mm minimum. The ground plane ring must be exposed metal and free of solder mask and silkscreen.

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







 





8.3

Minimum spacing is 0.127mm for all track to track, track to via, track to pad, via to via, via to pad and pad to pad spacing. USB Bus signal line and crystal line routing follows good practices for low noise emission. The USB and crystal connections should be as short as possible and have no radius turns greater than 45 degrees. The USB traces should be treated as 90 ohms differential and proper track to track (differential) spacing maintained. All vias should be tented with solder mask, except those in areas containing exposed, bare metal, and designed to be free of solder mask. The sensor solder pad sizes and solder mask openings should be as shown in the reference design. Thermal reliefs must be used on all pads and all vias which attach to a plane. No trace should enter a sensor BGA ball pad with a trace width greater than 40% of the diameter of the pad. Larger traces should be necked down prior to entering the BGA pad. For sensor boards integrated inside equipment, the sensor board ground is connected directly to chassis ground with a bolt or screw For peripheral modules, the USB cable includes a ferrite bead to suppress EMI transients.



Decoupling capacitors placed as close to sensor pins as possible



USB cable is shielded and shield is connected to chassis ground.

Industr ial Design Checkli st (sensor surf ace to casing sur face)  







 

Ensure full swipe finger contact with the surface of the sensor. Ample room in the finger guide to allow the slide to start from the joint (knuckle), for a standard finger (0.75 inches). The top surface of the casing should mate evenly with the top surfaces of the sides of the sensor. This includes the imaging surface and the “wings”. Any sloping into or out of the sensor in the slide path should not exceed 10 degrees of elevation angle. Side angle (sidewalls of the finger guide) should not exceed 45 degree elevation angle. If the sensor will be used for navigation, this angle should be reduced to 10 degrees elevation. Minimum spacing for the sensor edge to casing edge is 0.1mm. Sensor height post reflow (after assembly to the PCBA) is 0.86mm nominal at the imaging surface and 1.18mm high at the sensor wings. This is very important to note, or else the sensor will sit too low in the casing!

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8.4

Mechanical Design Checklis t (PCBA mou ntin g & mating to casing) 





8.5

The sensor must not be the alignment mechanism for mating the PCBA to the backside of the casing opening. Other alignment methods are required for the sensor to align with the sensor opening in the casing. Ensure alignment of the sensor with the rectangular opening BEFORE it gets inserted into the casing opening. Often this would mean an alignment method which has a height/depth of less than 2 mm and greater than 1.3mm for the sensor. If liquid cleansing is planned around the sensor, design for a casing sealing method – gasket seal or conformal coat of exposed PCBA areas around the casing opening.

Prototy pe or Unit Functio nal Valid ation Checkli st 



Power supply ripple (noise) confirmed on actual board to be less than 100mV peak-to-peak while D+ is active Reset timing meets requirements for specific clock or oscillator circuit used in design.



Reset voltage confirmed to rise to 3.0V



VDD rise time meets design value



VDD rises monotonically to its final value





VDD measured at the sensor falls to less than 0.5V within a few milliseconds when VDD is turned off If a crystal or resonator is used, start-up time confirmed to be less than 9ms on actual board using low capacitance oscilloscope probe

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9

Reference Design AuthenTec provides a Reference Design Kit (RDK) that includes a schematic and Bill of Materials for the USB interface. The Bill of Materials in this kit specifies readily available and inexpensive peripheral parts whenever possible. In some cases, finding RoHS compliant parts may entail longer lead times or greater costs for a product design. The sensor itself is RoHS compliant and lead-free. A block diagram of the Reference Design is shown in the figure below. A crystal oscillator and voltage regulation from 5.0V to 3.3V are provided as part of the design. If the USB port in the product can supply 3.3V for the sensor VDD, the voltage regulator section of the circuit can be omitted. The CLKSEL pins in this design are configured for a 12MHz crystal based operation.

VDD

AES2501B USB RDK

AES 2501B

USB 5.0V Power VDD Control

DPLUS

DPLUS

DMINUS

DMINUS

Voltage Regulator

PWR IN

OVC_DET CLKSEL2 CLKSEL1 CLKSEL0

CRYSTAL and passives

SYSCLK

RESET*

C

Figure 9-1 USB RDK Bloc k Diagram

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9.1

Reference Desig n Schematic

The AES2501B reference design schematic has the Universal Serial Bus (USB) interface. The reference schematic is shown below.

Figure 9-2 AES2501A Reference Design Schematic

10

USB Module

The AuthenTec Reference Design Kit includes a USB sensor module. This module consists of an AES2501B sensor and surrounding components, with an attached USB cable that can be inserted into a standard USB port on a PC.

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10.1 Purpose Of The Modul e The USB Module is intended to be used to develop application software for the fingerprint sensor before the actual production sensor board is available. It can also be used for preliminary evaluation testing and biometric testing. Since it can be connected directly to a PC’s USB port, there need be no time delay in starting software development or product concept evaluation.

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11 Troubleshooting Sensor Modules When a new sensor module has been developed for a product, various problems may be encountered. These problems may be either software or hardware related. To assist in debugging new modules, the following troubleshooting guidelines should be used. It is assumed that the module has been plugged into a USB port on a PC. This section is also intended to support those customers who are in production and need to identify failed or correct performing units. In order to avoid costl y rework, as well as to ensure maximum reliability and performance of the sensor, this section should be This section is intended for studied in detail before beginning troubleshooting. hardware integrator customers, system designers bringing up initial systems, and manufacturers and end customer systems where needed. For devices from AuthenTec which appear to be a supplier defect, AuthenTec has the RMA (Return Materials Authorization) and PFARR ( Product Failure Analysis Review Request) process to follow. Please contact your local or corporate AuthenTec personnel to facilitate further action.

11.1 Senso r Enumeration The most visible indication of a problem with a sensor module is when the sensor module is not enumerated correctly by the host computer. The host computer USB controller should enumerate the module upon plug-in. Enumeration can be checked by looking at the Device Manager in Windows. An example of the sensor enumeration as displayed in the Device Manager is shown in the figure below. The “AuthenTec AES2501x” device should be displayed.

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Figure 11-1 Sensor Enumeratio n (Device Manager)

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Figure 11-2 Device Driver Properties

There are at least four possible abnormal enumeration conditions that can occur. Any of these events may occur during normal operation or in response to an ESD event. 1. 2. 3. 4.

The sensor is not visible in the Device Manager at all. The sensor is shown as an unknown device or “Fingerprint Sensor”. The sensor is “banged” (shown with an exclamation point) in the Device Manager. The sensor re-enumerates intermittently.

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11.1.1 Sensor Not Vis ibl e In Device Manager If the sensor is not visible in the Device Manager, this is usually an indication of a hardware problem. Often this indicates a fatal problem like no sensor VDD voltage or a disconnected USB D+ or D- signal line. This problem can also occur if the sensor VDD is continually being switched on and off by the OVC_DET circuit. The first step in debugging this problem is to look at the basic sensor VDD, reset, OVC_DET, USB D+, USB D- and oscillator with an oscilloscope. Connect wires to the sensor board to monitor these signals and then plug the board into a USB port and monitor the appearance of these signal at the initial plug-in event and afterwards. The oscillator signal should always be monitored with a low capacitance oscilloscope probe. Triggering on the sensor VDD going from low to high will capture the events that occur at plug-in. Examples of normal signals are shown in the figures below.

Figure 11-3 Normal Sensor Signals At Plug -In

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Figure 11-4 Normal Sensor Signals Showing Oscillator Start-Up

If the sensor VDD fails to rise or it is continually switching on and off (as shown in the following figure), then this is the cause of the sensor failing to enumerate.

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Figure Figur e 11-5 11-5 Effect Of OVC_D OVC_DET ET Continuall Conti nually y Switchi ng VDD

In the figure above, the OVC_DET circuit is continually triggering, turning VDD on and off. The sensor VDD is never on for a long enough time to enable enumeration to occur. This phenomenon can have several causes that should be investigated: 1. The 2ohm current sense resistor (R4) may be a higher resistance value (in the figure above, a 180ohm sense resistor was used). 2. The 40.2Kohm current current limit control resistor resistor (R1) connected connected to the AAT46 AAT4610A 10A may not be 40.2Kohms 3. There may be a short short circuit in the circuit circuit board that is causing causing an excessive excessive amount of current to be drawn on the sensor VDD line. 4. The sensor itself may be physically damaged so that it is drawing an excessive amount of VDD current. Anothe Anotherr poss possibl ible e prob problem lem is that that the the oscil oscillat lator or does does not start start up at all, all, or or star starts ts after after 9ms. 9ms. If the oscillator does does not start up, up, then the sensor sensor will be unable unable to communicate. communicate. If the oscillator start-up time is longer than 9ms, the PLL may lock on the wrong frequency for a short time, causing causing USB communication to break break down. (The PLL will eventually reset reset to the correct frequency frequency as long as the oscillator is oscillating oscillating at the right frequency.) Another

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cause of this problem may be incorrect design of the oscillator circuit, or a defective or incorrect crystal or resonator. A third third possib possible le proble problem m is due to the sensor sensor RESET* RESET* signa signall never never rising rising,, or rising rising too soon. If the RESET* signal never rises, rises, then the sensor sensor will always stay in reset reset and will not communicate. communicate. If the RESET* signal rises too too soon, it may release release the sensor sensor from reset before the oscillator has stabilized, resulting in problems with the PLL locking on the wrong frequency again.

11.1 11.1.2 .2 Senso Sensorr Is Show n As An Unkn own Devic Device e If the sensor is shown as an unknown device (typically seen as a “Fingerprint Sensor” under “Other devices” with a question mark) in the device manager, as shown below, this may be an indication that the AuthenTec driver has not been installed.

Figur e 11-6 Unkn own Device Device

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There are other, more subtle problems that might cause this problem. If the sensor is physically damaged in such a way that the USB enumeration data has been corrupted, then an “unknown device” problem might occur. This type of problem should rarely occur, however. Likewise, if problems in the oscillator circuit cause the sensor PLL to lock on the wrong frequency, as described in the previous section, then USB communication may be erratic, resulting in the operating system being unable to identify the sensor.

11.1. 11.1.3 3 Senso Sensorr Is “ Banged” In The Device Device Manager When the sensor is displayed with an exclamation point in the Device Manager, this indicates that the driver was able to recognize the USB Vendor Identification Number (VID) and Product Identification Number (PID) of the sensor, but the register data read from the sensor was incorrect in some way. For example, the sensor version number read from the registers may not match the version expected by the driver, or other register data may be corrupted. This can occur because an an obsolete sensor sensor version has been placed placed on the PC board, or because of problems with USB communication. communication. First use the Windows Device Manager to try disabling and re-enabling the sensor to see if this fixes the problem, as shown in the figures below. below. Right click on on the “AuthenTec “AuthenTec AES1600 AES1600”” in the Device Device Manag Manager er and then selec selectt either either “Enable” “Enable” or “Disab “Disable” le” from the menu. When the sensor sensor is disabled, a red “X” will appear appear on the USB symbol to the right right of the sensor description. description. If the problem was er erratic ratic USB communication, communication, disabling and rereenabling the sensor may fix it, at least temporarily. For example, it is possible for for this phenomenon to occur during ESD testing due to the ESD event upsetting USB communication. communicat ion. In some cases, it may be necessary to shut down power to the PC and then reboot to fix this problem.

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Figure 11-7 Disabling And Enabling The Sensor

If the sensor is knocked out by an ESD event, first check to see if the OVC circuit is tripping and forcing a re-enumeration after ESD events. If the circuit never trips (OVC_DET signal never goes high), the 2ohm sense resistor may be an incorrect value, or there may be some other problem with the circuitry around the AAT4610A. Another possible problem is that the sensor VDD does not fall to less than 0.5V within a few milliseconds after VDD is turned off by the AAT4610A. If sensor VDD does not fall to less than 0.5V, latchups may never be cleared and the sensor will be in an improper operating state. A third problem that might occur is that the AuthenTec driver is unable to deal with a particular error condition. In this case, contact AuthenTec for assistance in working on the problem. If the sensor board is integrated inside the PC or other hardware and it is the PC USB port that is knocked out by an ESD event, then this is usually an indication of insufficient grounding within the hardware. A common problem is that the sensor board itself is not grounded to the hardware chassis. Try connecting the sensor board ground directly to the chassis to see if this solves the problem. Another problem occurs when the sensor is integrated inside of a PC or other hardware and the USB cable connecting the sensor board to the USB port is not shielded. ESD events generate huge EMI pulses that can be received by the USB cable, which behaves like an antenna if it is not shielded. A good indicator for this type of problem is that the

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sensor or USB port becomes “banged” in the device manager when ESD pulses are applied to the hardware casing away from the sensor. Try shielding the USB cable with grounded metal foil to see if this solves the problem.

11.1.4 Sensor Re-Enumerates Interm itt ently There are several possible problems that can cause the sensor to re-enumerate intermittently. First, the 2ohm sense resistor (R4) may be too high of a value, causing the OVC threshold to be marginally low. If this is the case, the sensor current may occasionally cross the threshold and cause the OVC circuit to turn off sensor power. This problem can be discovered by monitoring the OVC_DET and sensor VDD signals over a long period of time. Triggering the oscilloscope on the OVC_DET signal going high will capture this type of event. If the current limit control resistor (R1) of the AAT4610A is the wrong value or disconnected, this may cause the AAT4610 to intermittently turn off power to the sensor. If there is a problem with the oscillator circuit or oscillator start-up time being longer than 9ms, it is possible for the sensor PLL to lock on the wrong frequency. The sensor may draw too much current in this case, and if the oscillator start-up time is longer than the OVC detection time window (17.1 – 51.4ms), this may intermittently cause the OVC circuit to trigger. Monitoring the OVC_DET signal and sensor VDD over a long time will again capture this type of problem. Verify that the oscillator start-up time is less than 9ms and that RESET* goes high after the oscillator has stabilized. Also verify that the 47Kohm resistor in the oscillator circuit is really 47Kohms and is connected to the crystal. If the sensor is slightly physically damaged on its surface, causing mildly excessive current to be drawn, then again the OVC circuit may trigger intermittently. A more subtle problem can occur if the sensor VDD ripple exceeds the specified limit of 100mV peak to peak. Note that the maximum ripple occurs when the USB D+ signal is active, so the VDD ripple should be measured as shown in the figure below. This figure shows marginally good VDD ripple. Note that the VDD ripple is close to 100mV peak-topeak in this figure, but only when D+ is active. If the ripple exceeds specification, the sensor may re-enumerate intermittently. Adding decoupling capacitors and improving the PC board layout can improve this problem.

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Figure 11-8 Marginal VDD Ripple

11.2 Other Senso r Module Problems If the sensor enumerates properly, then many parts of the circuit are working correctly. However, other problems may occur. The best software tool for examining these problems is the DotNetDemo program from AuthenTec. This program allows an image of a fingerprint to be displayed by swiping a finger over the sensor surface, as shown in the figure below.

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Figure 11-9 Using DotNetDemo To Capture An Image

Use the Data Capture option of this program to display these images. There are a few different problems unrelated to USB enumeration that can occur: 1. A fingerprint image cannot be displayed. 2. The sensor consumes too much power or becomes uncomfortably warm. 3. Sensor does not wake up from suspend when a finger is placed on the sensor. 11.2.1 A Fingerpr int Image Cannot Be Displayed If an image of a fingerprint cannot be displayed, this may be caused by a problem with the sensor finger ring circuit. There is a 47ohm resistor connected between sensor pins A1 and D1 (the finger ring circuit). If this resistor is missing or disconnected, the sensor finger ring signal will not be present and the sensor will not be able to image. Test both sides of this resistor to see if there is an oscillating signal present, as shown in the figure below (signal labeled DRIVE_RING). If there is no signal on either side of this resistor, try replacing the sensor to see if it fixes the problem. If the signal is present on one side of the resistor but not the other, try replacing the resistor.

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DRIVE_RING

USB D+

VDDA_ON*

VDDA

Figure 11-10 Sensor Drive Ring Signal

Another problem that can prevent an image from being captured occurs when the sensor analog VDDA is not present. This may occur if the MOSFET connected to VDDA is missing or defective, or if there is some wiring problem in the PC board that causes VDDA to be disconnected. Monitoring VDDA with an oscilloscope, as shown in the figure above, will show if this is the case. Note that the DRIVE_RING signal is only present when VDDA is turned on. If the sensor is physically damaged, this may also prevent an image from being captured. Replacing the sensor is again a quick way to verify this problem.

11.2.2 Sensor Becom es Uncomfor tably Warm If the sensor becomes abnormally warm during operation, there are several possible problems to look for: 1. The sensor may have been physically damaged, causing excessive power consumption that is not triggering the OVC circuit. This may be because the damage

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is in the analog part of the circuit, or because the OVC circuit is not working. Check the OVC_DET signal with an oscilloscope to see if it is switching on and off, and use a high-resolution voltmeter to check the voltage drop on the 2ohm sense resistor. If the voltage drop is at or above the OVC threshold (40 – 100mV) but the OVC circuit is not triggering, check the components in the OVC circuit. The sensor OVC monitoring circuit may also fail due to the physical damage, so replacing the sensor is another option to try. If the voltage drop on the sense resistor is below the OVC threshold, then the damage is in the analog part of the sensor. Replace the sensor to see if this fixes the problem. 2. The sensor might have latched up due to an ESD event, and the latchup may not have been cleared by the OVC circuit. The analysis procedure is similar to when the sensor is damaged: check to see if the voltage drop on the sense resistor is above the OVC threshold, and whether the OVC circuit is triggering properly. Try turning off power to the sensor to see if the problem goes away. If it does not go away, the most likely problem is that the sensor is physically damaged, and not that an uncleared latchup event has occurred. If the problem goes away when the sensor power is turned off for a long time, verify that the sensor VDD falls to less than 0.5V within a few milliseconds after the power has been turned off by the AAT4610A. If it does not, this explains why a latchup occurred but could not be cleared. 3. The sensor VDD may be above the specification limit of 3.6V, overstressing the sensor. Check the VDD value with an oscilloscope to be sure that is continuously within specification over time. 4. There may be a short circuit or other wiring problem in the PC board causing improper voltages to be applied to some sensor pins. 11.2.3 Sensor Does Not Wake Up From Suspend If Remote Wakeup is enabled and the sensor fails to wake up from suspend when a finger is placed on it, there are at least two possible problems that should be investigated. First, if the oscillator startup time is longer than 20ms, the sensor will not be operational within the USB bus resume signaling specification and it will fail to wake up. Sensor VDD and other signals should also be investigated to be sure that they are behaving normally. Another cause for failure to wake up is when there is an interaction between the driver and the specific host platform. If all sensor module problems have been investigated and eliminated, contact AuthenTec for assistance with the driver.

11.3 Other Debug gin g Tips For investigating USB bus problems, the best tool to use is a USB Bus Analyzer. A Bus Analyzer can record and display all of the packets going to and from the sensor, greatly facilitating analysis of obscure driver and communication issues. If a Bus Analyzer is not available, it is also possible to use an oscilloscope to monitor bus traffic. In this case, the OE# signal from the sensor (default output from the GPO1 pin) can be used to help clarify

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the direction of the USB traffic. The OE# signal goes low when the USB transceivers in the sensor are active, so the low state of this signal indicates that it is the sensor that is transmitting the signals seen on the bus.

11.4 Hardware Debugging Summary This section is a summary of all the debugging tips provided above, for convenient reference. 1. Sensor not visible in Device Manager . Check the following: Is sensor VDD voltage 3.0 – 3.6V? If not, repair or replace sensor power supply.  Is VDD being continuously switched on and off by OVC_DET? If it is, check the  following: Is 2ohm sense resistor correct value? o Is 39K resistor connected to AAT4610A correct value? o Does PC board does have short circuit or wiring error? o Is sensor scratched or damaged? If so, replace sensor. o  Are reset signal voltage and timing correct? If not, replace reset capacitor.  Is Oscillator start-up time less than 9ms and is it the correct frequency? If not, check the following: Does crystal meet specifications? o o Is crystal capacitor is correct value? Is VDD ripple less than 100mV peak to peak while D+ is active? o Are IOSEL pins connected to VDD and ground correctly for crystal o frequency selected?  Are USB D+ and D- signals present and correct? 2. Sensor shown as “ Unknown Device” or “ Fingerprint Sensor” in Device Manager. Check the following:  Is correct driver installed? Is sensor scratched or damaged?  Is oscillator start-up time less than 9ms and is it the correct frequency? If not,  check the following: Does crystal meet specifications? o Is crystal capacitor is correct value? o Is VDD ripple less than 100mV peak to peak while D+ is active? o Are IOSEL pins connected to VDD and ground correctly for crystal o frequency selected? 3. Sensor is “ Banged” in Device Manager. Check the following: Is sensor version compatible with driver version?  Is USB communication noisy or erratic? 

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





Is Oscillator start-up time less than 9ms and is it the correct frequency? If not, check the following: Does crystal meet specifications? o Is crystal capacitor correct value? o Is VDD ripple less than 100mV peak to peak while D+ is active? o Are IOSEL pins connected to VDD and ground correctly for crystal o frequency selected? Can problem be fixed by disabling and re-enabling the sensor in the Device manager? Did problem occur as a result of ESD? If so, check the following: Does OVC_DET circuit trigger in response to ESD event-induced latchup? o Is 2ohm sense resistor correct value? o Is the circuitry connected to the AAT4610A correct? o Does sensor VDD fall to less than 0.5V within a few milliseconds when o OVC_DET signal goes high? Is the driver responding incorrectly to a particular error condition? (Contact o AuthenTec for assistance.) Is the PC’s USB port being knocked out by the ESD event? o For sensors integrated into equipment, is sensor board grounded to the o equipment chassis with a screw or bolt? For sensors integrated into equipment, is the USB cable to the sensor o shielded? o For peripheral devices, does the USB cable have a ferrite bead to suppress EMI transients?

4. Sensor re-enumerates intermittently. Check the following: Does OVC_DET signal trigger intermittently? If so, check the following:  Is 2ohm sense resistor (R4) correct value? o Is (R1) connected to AAT4610A correct value? o Is oscillator start-up time less than 9ms and correct frequency? o Is 47Kohm resistor in oscillator circuit correct value? o Is sensor scratched or damaged? o o Is VDD ripple less than 100mV peak-to-peak while USB D+ is active? Is USB communication noisy or erratic?  5. Fingerprint image cannot be displayed using Aware. Check the following: Is the 47ohm resistor (R5) in the finger drive ring circuit present and the correct  value? Does the finger ring signal exist during imaging mode?  Does sensor VDDA voltage exist and is it the correct value during imaging mode?   Is the sensor scratched or damaged? SR05 placed correctly (not rotated) when placed onto the board? 

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6. Sensor becomes uncomfortably warm. Check the following: Did sensor become warm after an ESD event? If so, check the following:  Does OVC_DET signal trigger in response to ESD events? If not, check o the 2ohm sense resistor and the circuitry connected to the AAT4610A. Does voltage across sense resistor exceed OVC_DET threshold? o Is 2ohm sense resistor correct value?  Is 40.2Kohm resistor connected to AAT4610A correct value?  Is sensor scratched or damaged?  Does sensor VDD exceed 3.6V?   Does the PC board have a short circuit or wiring error? 7. Sensor does not wake up from Suspend. Check the following: Is oscillator start-up time less than 9ms? If not, then check the following:  Does crystal meet specifications? o Is crystal capacitor correct value? o Is there a driver interaction with the specific host platform? (Contact AuthenTec  for assistance.) 8. Sensor does not go into Suspend or takes a long time to go into suspend. Check the following: Verify that the TVS on the design is within specification. Too much capacitance  will not allow the sensor to calibrate the finger detect. This may make the sensor think there is a finger on the sensor and prevent the sensor and the software from allowing to transition to suspend. 9. Sensor passes Checksensor pixel test portion of program but does not image. Check the following: Power down the circuit. Verify the resistance from FRNG to ground. If this is less  than 10k ohm. The sensor has apparently been physically damaged if this measurement is less than 1K ohm. See Figure 11-10 and the signal labeled DRIVE-RING. This signal will be highly attenuated by the effective short seen on the FRNG node.

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12 Glossary ATA /ATE BIT

Bit BOM BSP

Byte Chip Type CPU D+ DDR Drive Ring DX EMI ESD FAR

Finger Detect Finger Detect Packet FRR

Gain Control GPIO HIL Hardware Platform Integration Board ISR

Ability To Acquire / Ability To Enroll. Description of sensor and biometric system performance. Built-in Test. A sensor function that outputs a fixed pattern image frame (test image) for testing purposes. The pattern can be modified by changing a sensor register value. A single binary digit, which can take the value of either 1 or 0. Bill Of Material. List of components required in a design. Board Support Package. This is a collection of OEM Functions and the Hardware Interface Layer software. Board Support Package makes it possible for an OEM Functions and Windows CE operating software to access the particular Hardware Platform resources. BSP includes the OAL, Kernel and static Device Drivers. A group of 8 bits. Fixed value built into one of the sensor’s registers that uniquely defines the sensor identity. Central Processing Unit: e.g. a microcontroller (XScale) on a WinCE platform. A normally high USB bus signal used for data transfer. A normally low USB bus signal used for data transfer. In synchronous serial protocol, data received by a device. Metallic ring on the surface of the sensor that is used to inject a small signal into the user’s finger In synchronous serial protocol, data transmitted by a device. Electromagnetic Interference. Unwanted electromagnetic signals radiated by a circuit or system. Electrostatic Discharge. An electrical spark caused by static electricity. False Acceptance Rate. Measurement of the accuracy of a fingerprint matcher in terms of the frequency of incorrectly matching a fingerprint with the template of a different person. Operation performed by sensor and software to determine if a user has placed his finger on the sensor or not. Data group output from the sensor during a finger detect operation that can be used by the software to determine if a finger is present on the sensor or not. False Rejection Rate. Measurement of the accuracy of a fingerprint matcher in terms of the frequency of incorrectly rejecting a fingerprint for not matching a template that it should match. Software function that adjusts the amplification of the sensor imaging circuitry. General Purpose Input / Output (type of interface to the processor). Hardware Interface Layer. See Platform. PC board supplied by AuthenTec that includes the sensor and all possible interface options, which can be connected to a system development board in order to perform software development and integration. Interrupt Service Routine – a function that processes incoming interrupts, usually preempting other processes that may be running when the interrupt occurs..

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IST Matcher Mbps MIPS OAL OEM OVC Pixel Platform

PDA PID Power Cycling Rdson Read Registers RoHS RDK SCK SCR SDK Slice Stacked Image Swipe Swipe Buffer Software Platform Test Image USB VDD VID Vth Watchdog Timer

Interrupt Service Thread – a user mode device driver. Software that determines whether a newly-captured fingerprint image is the same as a fingerprint template stored in a database Megabits Per Second: a data transfer rate, in millions of bits per second. Millions of Instructions Per Second (processing rate of a microprocessor or computer) OEM Adaptation Layer – part of the BSP – it abstracts the Platform hardware to the Kernel and Device Drivers. Original Equipment Manufacturer – a maker of a portable device with AuthenTec’s sensor on it. Overcurrent detection (circuit) Single element of an imaging array. Hardware system (CPU, memory, buses, ports, I/O system, storage, timers) that is a basis for controlling peripherals and executing operating system software. Personal Digital Assistant. USB Product Identification number Turning the power to the sensor on and off repetitively. The on-resistance of a MOSFET Software operation that causes the sensor to return the values of all of its registers in sequential order, with each val ue preceded by its register address. An EU environmental regulation for the Restriction of certain Hazardous Substances, notably heavy metals like lead (Pb), in electronic devices. Reference Design Kit Serial Data Clock: data is shifted / latched on the rising or falling edge of the SCK Silicon Controlled Rectifier. Four layer silicon device that can be switched between a high and low resistance state. Software Development Kit. This is AE 4.0 SDK. A single image frame output from the sensor An array of individual image frames captured during a finger swipe and displayed or stored in sequential order To slide a finger tip along the surface of the sensor in order to capture an image Area of RAM reserved for holding all of the image frames (stacked image) output from the sensor In the scope of this document: Microsoft Windows CE .NET 4.x with all the necessary OEM functions customize to control the Hardware Platform. See “BIT”. Universal Serial Bus Power supply to the AES1510 sensor. USB Vendor Identification number Threshold voltage of a MOSFET. Gate voltage at which a MOSFET begins to have a low drain-source resistance. A timer that triggers some event after a fixed length of time. Usually the processor will restart the timer periodically to prevent the event from being triggered unless a fault condition occurs.

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3070_10_AE2501B_Primer

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