Chapter4 Microwave Amplifier

Dr. Cuong HuynhTelecommunications DepartmentHCMUT 1

Huynh Phu Minh Cuong [email protected]

Department of Telecommunications

Faculty of Electrical and Electronics Engineering

Ho Chi Minh city University of Technology

Chapter 4

Microwave Amplifier

MICROWAVE INTERGRATED CIRCUITS


Microwave Amplifier

Reference:

[1] D. M. Pozar, Microwave & RF Design of Wireless Systems

(Ch 6,9)

[2] R. Ludwig, RF Circuit Design: Theory & Applications (Ch

8,9)

[3] G. Gonzalez, Microwave Transistor Amplifiers Analysis and

Design

[4] R. Weber, Introduction to Microwave Circuit: Radio

Fequency & Design Applications (Ch 15 )

[5] G. Vendelin, Design of Amplifier and Oscillator Circuit

Design by S-Parameters Method

[6] B. Razavi, RF Microelectronics (Ch 5-9)

[7] S. Cripps, RF Power Amplifiers for Wireless Communications


Microwave Amplifier


1. Transducer Power Gain (GT ) & Stability

Dr. Cuong HuynhTelecommunications DepartmentHCMUT

Low power microwave transistor



High power microwave transistor



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 ZS and ZL.

Definition of Two-Port Power Gains

LT

avs

PG

P

Cong suat tieu thu tren tai

Cong suat kha dung co the cung cap t nguon

*in S

avs inP P



22

11

222

21

11

)1)(1(

outLS

LS

TS

SG

2

22

2

2

2

2

1

2

21

11

)1)(1(

S

SG

LinS

T

22

211211

1 S

SSS

L

Lin

11

211222

1 S

SSS

S

Sout




Power Gain Calculation



22

211211

1 S

SSS

L

Lin

11

211222

1 S

SSS

S

Sout



Which region

Stable / unstable ?


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 matching networks: 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.

Resistive matching networks: Good input and output matching can be obtained by using resistive matching networks, with a corresponding loss in

gain and increase in noise figure.

Negative feedback: 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 amplifiers: 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.

Distributed amplifiers: 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.



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

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Chapter4 Microwave Amplifier