Case Study:Amp3Analysis of a Distributed AmplifierPresented by Michael Steer

Reading:Chapter 18, Section 18.4 Based on material in Microwave and RF

Design: A Systems Approach, 2nd Edition, by Michael Steer. SciTech Publishing,

2013.Presentation copyright Michael Steer

MICROWAVE AND RF DESIGN

Index: CS_Amp3

Case Study Amp3:Analysis of a Distributed Amplifier

Slides copyright 2013 M. Steer.

2─18 GHz GaAs MESFET Amplifier

1

RFOutput

V+

VGRFInput

FET 1 FET 2 FET 3 FET 4 FET 5 FET 6

Multi-Octave Wideband Amplifier Design

● Instrumentation● Distribution networks● Military● Optical drivers● Desirable to have slightly positive gain slope● Usually low efficiency and low gain

Single Stage Wideband Amplifier Dilemma

CAPID=C1C=−0.346 pF

INDID=L1L=−0.67 nH

PORTP=2Z=68 Ohm

PORTP=1Z=22.9 Ohm

CAPID=C1C=−0.294 pF

SUBCKTID=S2NET="N32400a"

Distributed Amplifier Concept

1Z 0, 1g g 3Z 0, 3g g 4Z 0, 4g g R1

RS

2Z 0, 2g g

R 2 10, 1Z d d 20, 2Z d d 30, 3Z d d

T2 T3 T4 RL1T

40, 4Z d d

STAGE 2 STAGE 3STAGE 1 STAGE 4

Gate LineInput

OutputDrain Line

Distributed Amplifier Concept

1Z 0, 1g g 3Z 0, 3g g 4Z 0, 4g g R1

RS

2Z 0, 2g g

R 2 10, 1Z d d 20, 2Z d d 30, 3Z d d

T2 T3 T4 RL1T

40, 4Z d d

STAGE 2 STAGE 3STAGE 1 STAGE 4

Gate LineInput

OutputDrain Line

Gate line

Drain line

Breaking Down The Design

RFOutput

V+

VG

RFInput

FET 1 FET 2 FET 3 FET 4 FET 5 FET 6

TGA8220 MMIC distributed amplifier

TGA8220 MMIC distributed amplifier

27

26

25

24

23

22

20

19

18

21

28O

utpu

t pow

er a

t 1-d

B c

ompr

essi

on (

dBm

)

2 6 10 14 18Frequency (GHz)

8

7

5

4

3

6

Gai

n (d

B)

Measured output power

Modeled output power

Modeled gain

Measured gain

2 6 10 14 18Frequency (GHz)

14131211109876543210

MeasuredModeled

Pow

er a

dded

effi

cien

cy (

%)

Power Added Efficiency

Dynamic Loadlines

Dynamic Loadlines

100

50

070 14

(dB

m)

I D

V (V)DS

FET 1

100

50

070 14

(dB

m)

I DV (V)DS

FET 6

Summary

● Specialized skill– Many algorithms (in papers) for develop for scaling

transistors and transmission line impedances

– Main draw backs are compromised gain, , and NF