Multistage amplifiers - rationalepersonal.stevens.edu/~bmcnair/EE359-S13/class13.pdf · 18...
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16 Multistage amplifiers - rationale High input Z for minimal loading Low output Z for minimal impact from load High power output High gain
Transcript of Multistage amplifiers - rationalepersonal.stevens.edu/~bmcnair/EE359-S13/class13.pdf · 18...
16
Multistage amplifiers - rationale
High input Z for minimal
loading
Low output Z for minimal impact
from load
High power output
High gain
17
Multistage amplifiers - rationale
High input Z for minimal
loading
Low output Z for minimal impact
from load
High power output
High gain Conflicting requirements
18
Multistage amplifiers - rationale
(differential input for
noise immunity)
Low output Z for minimal impact
from load
High power output
High gain (in multiple stages)
High input Z for minimal
loading
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Multistage amplifiers (CMOS)
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Multistage amplifiers (CMOS)
Differential input
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Multistage amplifiers (CMOS) Current mirror
Differential input
22
Multistage amplifiers (CMOS) Current mirror
Differential input
Active load current mirror
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Multistage amplifiers (CMOS) Current mirror
Differential input
Output stage
Active load current mirror
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Multistage amplifiers (CMOS) Current mirror
Differential input
Output stage
Active load current mirror
Current source
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Multistage amplifiers (BJT)
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Multistage amplifiers (BJT)
Differential input
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Multistage amplifiers (BJT)
Differential input
Differential single ended 2nd stage
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Multistage amplifiers (BJT)
Differential input
3rd stage, plus DC shift Differential single ended 2nd stage
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Multistage amplifiers (BJT)
Differential input
Emitter follower output stage
3rd stage, plus DC shift Differential single ended 2nd stage
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Multistage amplifiers (BJT)
Differential input
Current sources
Emitter follower output stage
3rd stage, plus DC shift Differential single ended 2nd stage
2
Feedback
Ch 10
3
Motivation for feedback in systems
A
Typical amplifier
4
Motivation for feedback in systems
A
Gain variation due to component variation
Typical amplifier
in
out
5
Motivation for feedback in systems
A
Gain variation due to component variation
Typical amplifier
System nonlinearity
in
out
in
out
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Motivation for feedback in systems
A
Gain variation due to component variation
Typical amplifier
System nonlinearity
in
out
in
out
Frequency response f
7
Structure of feedback system
A Input Output
Forward gain stage
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Structure of feedback system
A Input Output
+
Means to change system input
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Structure of feedback system
A Input Output
+
Means to sample system output
10
Structure of feedback system
A Input Output
+
β
Means to use output to influence input
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Structure of feedback system
A Input Output
+
β
Means to use output to influence input
12
Structure of feedback system
A Input Output
+
β
Negative feedback
partially cancels input
-
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Structure of feedback system
A Input Output
+
β
-
xs xo
xf
xi
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Structure of feedback system
A Input Output
+
β
-
xs xi=xs-xf xo=Axi
xf=βxo
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Structure of feedback system
A Input Output
+
β
-
xs xi=xs-xf xo=Axi
xf=βxo
1o
fs
x AAx Aβ
= =+
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Structure of feedback system
A Input Output
+
β
-
xs xi=xs-xf xo=Axi
xf=βxo
1o
fs
x AAx Aβ
= =+
1fA β≈For large A:
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Gain desensitization
A Input Output
+
β
-
1o
fs
x AAx Aβ
= =+
( )21
1d
fdA A Aβ=
+
( )1
1f
f
dA dAA A Aβ
=+
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Gain desensitization
A Input Output
+
β
-
1o
fs
x AAx Aβ
= =+
( )21
1d
fdA A Aβ=
+
( )1
1f
f
dA dAA A Aβ
=+
The variation in the forward amplifier gain is reduced by 1/(1+Ab)
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Gain/bandwidth tradeoffs
A(s) Input Output
+
β
-
( )1 /
M
H
AA ss ω
=+
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Gain/bandwidth tradeoffs
A(s) Input Output
+
β
-
( )1 /
M
H
AA ss ω
=+
( )( )1 ( )fA sA sA sβ
=+
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Gain/bandwidth tradeoffs
A(s) Input Output
+
β
-
( )1 /
M
H
AA ss ω
=+
( )( )1 ( )fA sA sA sβ
=+
( )( )
1( )
1 ( / ) 1M M
fH M
A AA s
s Aβ
ω β+
=+ +
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Gain/bandwidth tradeoffs
A(s) Input Output
+
β
-
( )1 /
M
H
AA ss ω
=+
( )( )1 ( )fA sA sA sβ
=+
( )( )
1( )
1 ( / ) 1M M
fH M
A AA s
s Aβ
ω β+
=+ +
For closed loop:
Midband gain
( )1M
M
AA β+
Band limits
( )1Hf H MAω ω β= +1
HLf
MAωω
β=
+
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Gain/bandwidth tradeoffs
24
Reduction in nonlinear distortion
