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08.408 Analog Integrated Circuits Lab Manual 08.408

Analog Integrated Circuits Lab

CYCLE 1: Introduction to Op-amp, Op-amp, Open loop frequency response,transfer characteristics characteristics Measurement of Op-Amp Parameters.-dc and ac characteristics Inverting amplifier ,Non inverting amplifiers, Adder ,Difference Amplifier ,Subtractor, Differential Integrator, Differentiator amplifier (one and 2 op-amp ),Instrumentation amplifier Integrator,

CYCLE 2: , Op-amp as a Comparator and voltage level detector. Voltage comparator LM311,Window Comparator using LM311.

Wave form generators :Astable, Monostable and Schmitt trigger circuit using Op -Amps. Triangular Triangular and square wave generators using op-amps. Oscillators:Wein Oscillators:Wein bridge oscillator using op-amp with amplitude stabilization and amplitude control,

RC Phase shift Oscillator. Oscillator. Precision rectifiers using Op-Amp,Clipping ,Clamping CYCLE 3: Active Filter Design Active second order filters using Op-Amp (LPF, HPF, BPF and BSF(notch)) Filters using gyrator circuits

CYCLE 4: Data conversion circuits A/D converters- counter ramp and flash type. D/A Converters- ladder circuit. IC voltage regulators (723), low & high voltage regulation Short circuit and Fold back protection.

Department of ECE ,VKCET

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08.408 Analog Integrated Circuits Lab Manual

Introduction to Operational amplifier

A complete op amp is realized by combining analog circuit building blocks. The bipolar op-amp has the general purpose variety and is designed to fit a wide range of specifications.

The op-amp contains 24 transistors, transistors, few resistors and only one capacitor Two power supplies Short-circuit protection


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Characteristics of the Ideal Op-amp

Differential input resistance is infinite. Differential voltage gain is infinite. CMRR is infinite. Bandwidth is infinite. Output resistance is zero. Offset voltage and current is zero. No difference voltage between inverting and noninverting terminals. No input currents.


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08.408 Analog Integrated Circuits Lab Manual Operational Amplifier: Open Loop configurations

To wire and test the ope rational amplifier (μA741) in its open loop configurations Aim: To Components required : CRO (20Mhz ,dual channel) Resistors Signal generator Oscilloscope probes ua741 opamp, capacitors,multimeters

Theory : Three open loop OPAMP configurations. configurations. The Differential Amplifier:

Figure shows the open loop differential amplifier in which input signals vin1 and vin2 are applied to the positive and negative input terminals. Since the OPAMP OPAMP amplifies the difference the between the two input signals, this configuration is called the differential amplifier. amplifier. The OPAMP OPAMP amplifies both ac in1 and R in2 in2 are normally negligible compared to the input and dc input signals. The source resistance R in1 resistance R i. Therefore voltage drop across these resistances can be assumed to be zero. Therefore v1 = vin1 and v2 = vin2. vo = Ad (vin1 – vin2 ) where, Ad is the open loop gain. The Inverting Amplifier: If the input is applied to only inverting terminal and non-inverting terminal is grounded then it is ca lled


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08.408 Analog Integrated Circuits Lab Manual inverting amplifier. amplifier.

v1= 0, v2 = vin. vo = -Ad vin

The negative sign indicates that the output voltage is out of phase with respect to input 180 ° or is of opposite polarity. polarity. Thus the input signal is amplified and inverted . The non-inverting amplifier: In this configuration, the input voltage is applied ap plied to non-inverting terminals and inverting terminal is grounded

v1 = +vin , v2 = 0 vo = +Ad vin

In all there configurations any input signal slightly greater than zero drive the output to saturation level. This is because of very high gain. Thus whe n operated in open-loop, the output of the OPAMP OPAMP is either negative or positive saturation or switches between positive and negative saturation levels. Department of ECE ,VKCET

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08.408 Analog Integrated Circuits Lab Manual Therefore open loop op-amp is not used in linear applications. Observation: Result: Differential amplifier : Out put voltage= for an input voltage of Vin1________ and Vin2 ______ Inverting Amplifier : Out put voltage= for an input voltage of ______

Non-Inverting Amplifier : Out put voltage= for an input voltage of ______ Op-amp- transfer characteristics Aim: To wire and test the operational amplifier (μA741) and observe its open loop transfer characteristics


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Voltage Transfer characteristic of an operational amplifier

Observation Result : Positive and negative saturation voltages+Vsat=


and -Vsat =

from transfer transfer characteristic

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08.408 Analog Integrated Circuits Lab Manual FREQUENCY RESPONSE OF OPAMP Aim : To test and verify the open loop frequency response of the operational amplifier (μA741)


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Procedure:

1) Now input a sine wave [1Vpp - 5 Hz – zero DC offset] between (+) and (-).

2) Observe the output using an oscilloscope.

3) Now sweep the frequency from 5 Hz to 1MHz.

4) Draw the frequency response and phase margin graphs in logarithmic sheets.

Analysis:

a) Find the 3-db point and the unity gain frequency. frequency. b) What is the phase lag at the point of unity gain?


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08.408 Analog Integrated Circuits Lab Manual Operational Amplifier: Closed Loop configurations

To wire and test the operational amplifier (μA741) in its closed loop configurations Aim: To Closed Loop Amplifier: A closed loop amplifier can be represented by two blocks one for an OPAMP OPAMP and other for a feedback circuits. There are four following ways to connect these blocks. These connections are classified according to whether the voltage or current is feedback to the input in series or in parallel: Voltage – series feedback Voltage – shunt feedback Current – series feedback Current – shunt feedback    

the signal direction is from input to output for OPAMP OPAMP and output to input for feedback circuit. Only first two, feedback in circuits are important. Voltage series feedback:

It is also called non-inverting voltage feedback circuit. With With this type of feedback, the input signal drives the non-inverting input of an amplifier; amp lifier; a fraction of the output voltage is then fed back to the inverting input. The op-amp is represented by its symbol including its large signal voltage gain Ad or A, f and the feedback circuit is composed of two resistors R 1 and R f Department of ECE ,VKCET

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The feedback voltage always opposes the input voltage, (or is out of phase by 180° with respect to input voltage), hence the feedback is said to be negative. The closed loop voltage gain is given by


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The product A and B is called loop gain. The gain loop gain is very large such that AB >> 1

This shows that overall voltage gain of the circuit equals the reciprocal of B, the feedback gain. It means that closed loop gain is no longer dependent on the gain of the op-amp, but depends on the feedback of the voltage divider. divider. The feedback gain B can be precisely controlled and it is independent of the amplifier. amplifier. The gain is approximately constant, even though differential voltage gain may change. Suppose A increases for some reasons (temperature change). Then the output voltage will try to increase. This means that more voltage is fedback to the inverting input, causing vd voltage to decrease. This almost completely offset the attempted increases in output voltage. Similarly, Similarly, if A decreases, The output voltage decreases. It reduces the feedback voltage vf and hence, vd voltage increases. Thus the output voltage increases almost to same level. Again considering the voltage equation, vO = Ad vd or vd = vO / Ad Since Ad is very large (ideally infinite) vO \ vd » 0. and v1 = v2 (ideal).


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08.408 Analog Integrated Circuits Lab Manual This says, that the voltage at non-inverting input terminal of an op-amp is approximately equal to that at the inverting input terminal provided that Ad is very large. This concept is useful in the analysis of closed closed loop OPAMP OPAMP circuits. circuits. For example, example, ideal closed loop voltage voltage again can be obtained obtained using the results

Voltage shunt Feedback:

The input voltage drives the inverting terminal, and the amplified as well as inverted ou tput signal is f. This arrangement forms a negative also applied to the inverting input via the feedback resistor R f feedback because any increase in the output signal results in a feedback feedba ck signal into the inverting input signal causing a decrease in the output signal. The non-inverting terminal is grounded. Resistor R 1 is connected in series with the source. The closed loop voltage gain can be obtained by, writing Kirchoff's current equation at the input node V2.


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The negative sign in equation indicates that the input and output signals are out of phase by 180. f and R 1 Therefore it is called inverting amplifier. The gain can be selected by selecting R f

Inverting Input at Virtual Ground: In the figure shown earlier, the non-inverting terminal is grounded and the- input signal is applied to the inverting terminal via resistor R 1. The difference input voltage vd is ideally zero, (vd= vO/ A) is the voltage at the inverting terminals (v2) is approximately equal to that of the non-inverting terminal (v1). In other words, the inverting terminal voltage (v1) is approximately at ground potential. Therefore, it is said to be at virtual ground.


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Voltage Follower: As shown in figure , connect the output of the op-amp directly to the ‘-‘input and connect the output of the function generator to the ‘+’ input of the op-amp.

After turning on the power, confirm that the input and output signals are identical and that the voltage follower is non-inverting. Record the input and output amplitudes.


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Inverting summer: Again, for an ideal OPAMP, v1 = v2. The current drawn by OPAMP OPAMP is zero. Thus, applying KCL at v2 node This means that the output voltage is equal to the negative sum of all the inputs times the gain of the f/ R; hence the circuit is called f= R then the output voltage is circuit R f c alled a summing amplifier. When When R f equal to the negative sum of all inputs.

vo= -(va+ v b+ vc) If each input voltage is amplified by a different factor in other words weighted differently at the output, the circuit is called then scaling amplifier. amplifier.


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The circuit can be used as an averaging circuit, in which the output voltage is equal to the average of all the input voltages. b= R c = R and R f f / R = 1 / n where n is the number of inputs. Here R f f / R = 1 / 3. In this case, R a= R

vo = -(va+ v b + vc) / 3 Non Inverting Summer

With two inputs vo is the weighted sum of the inputs. vo =v1 + v2 (for all resistors equal) vo = (R 1+R 2)/R 2 (v1 R 4 + v2R 3)/ (R 3+R 4)

vo =v1 + v2 +v3 (for R 1 = 2R 2 and R 3=R 4=R 5) vo = {(R 1+R 2)/R 2} { (v1 R 4||R 5)/(R 4||R 5+R 3) + (v2R 3||R 5)/(R 3||R 5+R 4) + (v3R 3||R 4) /(R 3||R 4+R 5)}

Differential Amplifier


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Differential Amplifier We have used only one of the operational amplifiers inputs to connect to the amplifier, using either the "inverting" or the "non-inverting" input terminal to amplify a single input signal with the other input b+ + ing connected to ground. But we can also connect signals to both of the inputs at the same time producing another common type of operational amplifier circuit called a Differential Amplifier

By connecting each input inturn to 0v ground we can use superposition to solve for the output voltage Vout. Then the transfer function for a Differential Amplifier circuit is given as:


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When resistors, R1 = R2 and R3 = R4 the above transfer function for the differential amplifier can be simplified to the following expression: If all the resistors are all of the same ohmic value, that is: R1 = R2 = R3 = R4 then the circuit will become a Unity Gain Differential Amplifier and the voltage gain of the amplifier will be exactly one or unity. Then the output expression would simply be Vout=V2-V1. Vout=V2-V1. Differential Amplifier circuit is a very useful op-amp circuit and by adding more resistors in The Differential paral parallel lel with the input resist resistors ors R1andR3, R1andR3, the resultant resultant circuit circuit can be made made to either either "Add" or "Subtract" the voltages applied to their respective inputs. One of the most common ways of doing this is to connect a "Resistive Bridge" commonly called a Wheatstone Bridge to the input of the amplifier as shown below. below.


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Bridge Amplifier

The standard Differential Amplifier circuit now becomes a differential voltage comparator by "Comparing" one input voltage to the other. For example, by connecting one input to a fixed voltage reference set up on one leg of the resistive bridge network and the other to either a "Thermistor" or a "Light Dependent Resistor" the amplifier circuit can be used to detect either low or high levels of temperature or light as the output voltage becomes a linear function of the changes in the active leg of the resistive bridge and this is demonstrated below


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Here the circuit above acts as a light-activated switch which turns the output relay either "ON" or "OFF" as the light level detected by the LDR resistor exceeds or falls below a pre-set value at V2 determined by the position of VR1. A fixed voltage reference is applied to the inverting input terminal V1 via the R1 - R2 voltage divider network and the variable voltage (proportional to the light level) applied to the non-inverting input terminal V2. It is also possible to detect temperature using this type of circuit by simply replacing the Light Dependent Resistor (LDR) with a thermistor. By interchanging the positions of VR1 and the LDR, the circuit can be used to detect either light or dark, or heat or cold using a thermistor One major limitation of this type of amplifier design is that its input impedances are lower compared to that of other operational amplifier configurations, for example, a non-inverting (single-ended input) amplifier. Each input voltage source has to drive current through an input resistance, which has less overall impedance than that of the op-amps input alone. This may be good for a low impedance source such as the bridge circuit above, but not so good for a high impedance source.

One way to overcome this problem is to add a Unity Gain Buffer Amplifier such as the voltage follower seen in the previous tutorial to each input resistor. This then gives us a differential amplifier circuit with very high input impedance and low output impedance as it consists of two non-inverting buffers and one differential amplifier. amplifier. This then forms the basis for most "Instrumentation Amplifiers".

Instrumentation Amplifier Instrumentation Amplifiers (in-amps) are high gain differential amplifiers with high input impedance and a single ended output and are mainly used to amplify very small differential signals from strain gauges, gauges,the thermo rmocoup couples les or curren currentt sensin sensing g resist resistors ors in motor motor control control system systems. s. Unlike Unlike standar standard d operational amplifiers in which their closed-loop gain is determined by an external resistive feedback conne connect cted ed betw between een its its outp output ut term termin inal al and one one inpu inputt term termin inal al,, eith either er posi positi tive ve or negat negativ ive, e, instrumentation amplifiers have an internal feedback resistor that is effectively isolated from its input terminals as the input signal is applied across two d ifferential inputs, V1 and V2. The instrumentation amplifier also has a very good common mode rejection ratio, CMRR (zero output when V1=V2) well in excess of 100dB at DC. A typical example of a three op-amp instrumentation Department of ECE ,VKCET

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08.408 Analog Integrated Circuits Lab Manual amplifier with a high input impedance (Zin) is g iven below:

High Input Impedance Instrumentation Amplifier

The negative feedback of the top op-amp causes the voltage at Va to be equal to the input voltage V1. Likewise, the voltage at Vb is equal to the value of V2. This produces a voltage drop across R1 which is equal to the voltage difference between V1 and V2, the differential input voltage. This voltage drop causes a current to flow through R1, and as the two inputs of the buffer op-amps draw no current (virtual earth), the same amount of current flowing through R1 must also be flowing through the two resistors R2. This then produces a voltage drop b etween points Va Va and Vb equal to:

This voltage drop between points Va and Vb is connected to the inputs of the differential amplifier which amplifies it by a gain of one, (assuming that R3 = R4). Then we have a general expression for Department of ECE ,VKCET

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08.408 Analog Integrated Circuits Lab Manual overall voltage gain of the instrumentation amplifier circuit as:

Since the amplified input voltage now appears differentially across the resistor network consisting of R2, R1 and R2, the differential gain of the circuit can be changed simply by changing the value of R1 as we have seen previously 2 opamp Instrumentation Amplifier

A two-op two-op-am -amp p instru instrumen mentat tation ion amplif amplifier ier can also also be used used to make make a high-i high-input nput impedance impedance DC differential amplifier. As in the two-op-amp circuit, this instrumentation amplifier requires precise resistor matching for good CMRR. R4 should equal to R1 and R3 should equal R2


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3 op-amp instrumentation amplifier

We can change the differential gain of the instrumentation amplifier simply by changing the value of gain. We could still change the overall gain by changing the values of some of the other one resistor: R gain resist resistors ors,, but this this would would necessi necessitat tatee balanced resi resist stor or value value chan changes ges for for the the circ circui uitt to rema remain in gain symmetrical. Please note that the lowest gain possible with the above circuit is obtained with R gain completely open (infinite resistance), and that gain value is 1


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The final stage of this instrumentation amplifier is a differential-input, differential-output amplifier, with two voltage followers feed its inputs. These two voltage followers assure that the input impedance is over 100M. R3 should equal R1 and R4 equal R2. The gain of this instrumentation amplifier is set by the ratio of R2/R1. For good CMRR over temperature, low drift resistors should be used. Matching of R3 to R1 and R4 to R2 affects affects the CMRR. Making R4 slightly smaller smaller than R2 and adding a trim pot equal to twice the difference between R2 and R4 will allow the CMRR adjustment Instrumentation amplifier applications-Differential Instrumentation Amplifier with a

Bridge Transducer


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The cir circui cuitt sho shown wn in Fi Figur gure e 1 is a sim simple ple di diff ffere erenti ntial al ins instru trumen mentat tation ion amp ampli lifie fierr tha thatt has a res resist istive ive transducer (Rt).A resistive transducer is a device whose resistance changes when a certain physical energy applied to it changes. Common examples include transducers with resistances that vary with temperature, pressure, and light shining on it. As in most bridge circuits, the components in this circuit's bridge network (consisting of Ra, Rb, Rc, and Rt) are chosen so that the bridge is balanced at a certain reference condition, i.e., Rc/Rb = Rt/Ra.One way to do this is to make Ra=Rb=Rc=Rt=R at the chosen reference point. When the bridge above is balanced, Va = Vb, causing the input voltages to A3 to be equal and the output of A3 to be zero. When the resistance of Rt changes, however, the bridge becomes unbalanced, causing a non-zero voltage Vab to appear across the inputs of A3. This, in turn, results in an output voltage Vo that is proportional to the change in resistance of Rt, i.e., Vo = (RF/R1)(ΔR/4R) Vdc where ΔR is the change in Rt's resistance.

Result:The voltage output of the inverting and non inverting closed loop amplifier are …....Vp-p and ….Vpp ( for various gain -greater than 1 or o r less than one and equal to 1)

The voltage output of the inverting summer summer to the …....... inputs is …....V The voltage output of the non -inverting summer to the …....... inputs is …....V The voltage output of the sub-tractor to the …....... inputs is …....V The voltage output of the differential differential amplifier to the …....... inputs is …....V The voltage output of the 2 op-amp differential differential amplifier to the …....... inputs is …....V The voltage output of the instrumentation instrumentation amplifier to the …....... inputs is is …....V Conditions for which good integration happens is ….................. fa=.......... Hz, fb=..........Hz Conditions for which good differentiation happens is ….................. fa=.......... Hz, fb=..........Hz, fc =..............Hz


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