Berkeley
Broadband Amplifiers
Prof. Ali M. Niknejad and Dr. Ehsan Adabi
U.C. Berkeley
Copyright
c
2014 by Ali M. Niknejad
Niknejad
Advanced IC’s for Comm
Outline
Broadband Amplifiers
Shunt-Peaking
Distributed Amplifiers
Multi-section Matching (Bode-Fano Limits)
Transformer Matching Networks
Niknejad
Advanced IC’s for Comm
Cascade Amplifier Bandwidth Shrinkage
Consider an amplifier consisting of a cascade of identical
single-pole stages
G
0
G
(s) =
1 +
sτ
The bandwidth of
n
stages can be derived as follows
n
G
0
G
n
(s) =
G
(s) =
(1 +
sτ
)
n
n
n
n
n
G
0
G
0
G
0
|G
n
(jω
0
)| =
=
√
=
2
|1
+
jω
0
τ
|
n
|1
+
ω
0
τ
2
|
n
2
2
2
1/n
−
1 =
ω
0
τ
2
ω
0
τ
=
2
1/n
−
1
Bandwidth shrinks rapidly compared to the single stage.
Three stages =⇒ bandwidth drops by half
Niknejad
Advanced IC’s for Comm
Common Source Amplifier Bandwidth
R
L
C
gd
R
s
C
L
C
gs
Classic amplifier has several poles. The poles can be
calculated as
τ
gs
=
C
gs
R
s
τ
gd
=
C
gd
(R
s
+
R
L
+
g
m
R
s
R
L
)
τ
L
=
C
L
R
L
||r
o
Niknejad
Advanced IC’s for Comm
Minimizing the effect of
C
in
R
L
R
L
M3
C
L
M2
C
L
R
s
R
s
M1
The effect of
C
gd
can be minimize with a cascode
configuration.
The load can be isolated with a buffer M3 (τ
L
can be reduced)
Niknejad
Advanced IC’s for Comm
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