Chapter4 Microwave Amplifier

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Chapter 4

Microwave Microwave Amplifier

Huynh Phu Minh Cuong [email protected] Department of Telecommunications Faculty of Electrical and Electronics Engineering Ho Chi Minh city University of Technology

Microwave Amplifier Reference: [1] D. M. Pozar, M i crowa cr owave ve & RF D esi gn of Wir Wi r el ess Syste ystems ms (Ch 6,9) 6,9)

[2] R. Ludwig, RF Cir cui t D esi gn: The Th eory & Appli Appli cations (Ch 8,9)

[3] G. Gonzalez, M i crowave crowave Tr ansi ansi stor A mpli f i er s A nalys nal ysii s and Design

[4] R. Weber, Introduction to Microwave Circuit: Radio F equency quency & D esi gn Appli cati cati ons (Ch 15 ) [5] G. Vendelin, Design of Amplifier and Oscillator Circuit D esi gn by S-Par S-Par amete ameterr s M ethod th od [6] B. Razavi, RF M i croel croel ectroni cs (Ch 5-9) [7] S. Cripps, RF Powe Powerr A mpli f i er s f or Wir Wi r el ess Commun Commun i cati cati ons

Microwave Amplifier

Microwave Amplifier

Microwave Amplifier

Microwave Amplifier

1. Transducer Power Gain (GT ) & Stability


Low power microwave transistor


High power microwave transistor


1. Transducer Power Gain (GT ) & Stability Definition of Two-Port Power Gains

A two-port network with arbitrary source and load impedances.

Transducer power gain = GT = PL /Pavs is the ratio of the power delivered to the load to the power available from the source. This depends on both Z S and Z L.

GT

P Coâng suaát tieâu thuï treân taûi   Coâng suaát khaû duïng coùtheå cung caáp töø nguoàn P

L

avs

Pavs  P in

* in  S




GT 

GT 

S 21

2

(1 

S

2

)(1 

 L

2

1  S S 11 1   L out S 21

2

(1 

1 2

2

)(1 

2

2

1  S in 1   L S 22

2

2 2

)

)

in  S 11 

ou t  S 22 

S 12 S 21 L

1   L S 22 S 12 S 21S

1  S S 11

Power Gain Calculation


in  S 11 

S 12S 21 L

1   L S 22

ou t  S 22 

S 12 S 21S

1  S S 11




Which region Stable / unstable ?













1. Transducer Power Gain (GT (GT ) & Stability

1. Transducer Power Gain (GT (GT ) & Stability

2. Maximum Transducer Transducer Power Gain Design



2. Maximum Transducer Power Gain Design








3. Constant Gain Circles and Specified Gain Amplifier Unilateral Transistor








4. Low Noise Amplifier (LNA)



Receiver sensitivity is mainly determined by LNA noise figure.






Constant noise figure circles in the

s plane

For a fixed noise figure F, we can show that this result defines a circle in the S plane.

Define the noise figure parameter, N, as







5. BROADBAND TRANSISTOR AMPLIFIER DESIGN  Compensated matchi ng networ ks : Input

and output matching sections can be designed to compensate for the gain rolloff in |S21|, but generally at the expense of the input and output matching.  Resisti ve matchi ng networ ks: Good input and output matching can be obtained by using resistive matching networks, with a corresponding loss in gain and increase in noise figure.  Negati ve f eedback: Negative feedback can be used to flatten the gain response of the transistor, improve the input and output match, and improve the stability of the device. Amplifier bandwidths in excess of a decade are possible with this method, at the expense of gain and noise figure.  Balanced ampli f ier s: Two amplifiers having 90 couplers at their input and output can provide good matching over an octave bandwidth, or more. The gain is equal to that of a single amplifier, however, and the design requires two transistors and twice the DC power.  Di str ibuted amplif i er s : Several transistors are cascaded together along a transmission line, giving good gain, matching, and noise figure over a wide bandwidth. The circuit is large, and does not give as much gain as a cascade amplifier with the same number of stages. ◦

5. BROADBAND TRANSISTOR AMPLIFIER DESIGN




5. BROADBAND TRANSISTOR AMPLIFIER DESIGN The concept of the distributed amplifier dates back to the 1940s, when it was used in the design of broadband vacuum tube amplifiers. Bandwidths in excess of a decade are possible, with good input and output matching. Distributed amplifiers are not capable of very high gains or very low noise figure, however, and generally are larger than an amplifier having comparable gain over a narrower bandwidth. This type of circuit is also known as a traveling wave amplifier.


6. Power Amplifier (PA) Design

















Chapter4 Microwave Amplifier

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