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
