Coupling and Bypass Capacitor Design Since impedance of a capacitor increases with decreasing frequency, coupling and bypass capacitors reduce amplifier gain at low frequencies.. To
Trang 1EE 322
Electronics II
Lecture 10 Coupling and Bypass Capacitor Design
Trang 2Coupling and Bypass Capacitor Design
Since impedance of a capacitor increases with decreasing
frequency, coupling and bypass capacitors reduce amplifier gain at low frequencies.
To choose capacitor values, short-circuit time constant
method is used: each capacitor is considered separately
with all other capacitors replaced by short circuits.
To neglect a capacitor, the magnitude of capacitive
impedance must be much smaller than the equivalent
resistance appearing at its terminals.
Jaeger/Blalock
7/1/03
Microelectronic Circuit Design
McGraw-Hill
Chap 14 - 2
Trang 3Coupling and Bypass Capacitor Design: C-E
and C S Amplifiers
Consider C 1 (with v i =0): using
short-circuit time constant technique , look at each capacitor on its own each
capacitor on its own each time, and short other
capacitors
To neglect C 1 , its impedance must be much smaller than (R I +R in )
C C
in R R C
10 1
1 1
1
Jaeger/Blalock
7/1/03
Microelectronic Circuit Design
McGraw-Hill
Chap 14 - 3
R I R in C R I R in
C
1
Trang 4Coupling and Bypass Capacitor Design: C-E
and C S Amplifiers
RiB R
R
For C-E amplifier,
RiB B
R in
R
For C-S amplifier,
RiG R
R
G in
For coupling capacitor C1,
R I R in C R I R in
C
10 1
1 1
is chosen to be lowest frequency for which midband operation is needed in given application.
Jaeger/Blalock
7/1/03
Microelectronic Circuit Design
McGraw-Hill
needed in given application.
Chap 14 - 4
Trang 5Coupling and Bypass Capacitor Design: C-E
and C S Amplifiers
For C-E amplifier,
RiC R
R
C3
RiC C
R out
R
For C-S amplifier,
RiD
R D out
R out D iD
For coupling capacitor C3,
C3
R R out C R R out
C
3
10 3
3
1
is chosen to be lowest frequency for which midband operation is needed in given application
Jaeger/Blalock
7/1/03
Microelectronic Circuit Design
McGraw-Hill
needed in given application.
Chap 14 - 5
Trang 6Coupling and Bypass Capacitor Design: C-E
and C-S Amplifiers (contd.)
In this case, we can neglect impedances
of capacitors C1 and C3, find the equivalent resistance looking up into emitter or source of amplifier.
m g E R R
C
1 4
1 2
C2
C
1
1 2
m g S
R
4
C2
Jaeger/Blalock
7/1/03
Microelectronic Circuit Design
McGraw-Hill
Chap 14 - 6
Trang 9Coupling and Bypass Capacitor Design: C-E
and C-S Amplifiers (Example) p ( p )
Given data: f = 1000Hz, values of all resistors and input and output f , p p
resistances for C-E.
?
in R
?
?
1
C
in
R I R
C
( 1 / ) ?
1
C
? 2
) /
1 ( 4
C
m
g E
R R
C
Jaeger/Blalock
7/1/03
Microelectronic Circuit Design
McGraw-Hill
3
Chap 14 - 9
Trang 10Coupling and Bypass Capacitor Design: C-E
and C-S Amplifiers (Example) p ( p )
kΩ 1 78
B
R in
R
F 02 0
1 99nF
in
R I R C
( 1 / ) 67 . 2 nF
1
C
F 0.68 2
) /
1 ( 4
C
m
g E
R R
3
R R out
Jaeger/Blalock
7/1/03
Microelectronic Circuit Design
McGraw-Hill
Chap 14 - 10
Trang 11Coupling and Bypass Capacitor Design: C-E
and C-S Amplifiers (Example) p ( p )
resistances for C-S amplifier
resistances for C S amplifier.
kΩ 892
G
R in
R
1 178pF
1
in
R I R
C
1 55 . 3 nF
C
F 0.56 2
) /
1 ( 6
2
C
m
g S
R R
F 015 0
F 31 1
1
C
C 1 31 nF 3 0 015 F
3
1
out R R
C
Jaeger/Blalock
7/1/03
Microelectronic Circuit Design
McGraw-Hill
Chap 14 - 11
Trang 12Coupling and Bypass Capacitor Design: C-C
and C-D Amplifiers
For C-C amplifier,
RiB B
R in
R
For C-D amplifier,
RiG G
R in
R
For coupling capacitor C1,
in
R I R
C
1 1
Jaeger/Blalock
7/1/03
Microelectronic Circuit Design
McGraw-Hill
Chap 14 - 12
Trang 13Coupling and Bypass Capacitor Design: C-C
and C-D Amplifiers
For C-C amplifier,
C
RiE R
out
For C-D amplifier,
C3
RiS R
out
For coupling capacitor C3,
C3
R R out
C
3
Jaeger/Blalock
7/1/03
Microelectronic Circuit Design
McGraw-Hill
Chap 14 - 13
Trang 14Coupling and Bypass Capacitor Design:
C-C and C-D Amplifiers (Example)
resistances for both C-E and C-S amplifiers.
For C C amplifier: For C-D amplifier:
For C-C amplifier:
kΩ 5 95
B
R in
G
R in R
89pF
1
C
out
pF 8200 1
816pF
1 1
C
in
R I R
C
pF 1000 1
89pF 1
C
in
R I R
C
6
pF 8200 1
C
pF 8200
pF
795 3
1 3
C
out R R
C
pF 8200 3
pF
782 3
1 3
C
out R R
C
Jaeger/Blalock
7/1/03
Microelectronic Circuit Design
McGraw-Hill
pF 8200
3
Chap 14 - 14
Trang 15Coupling and Bypass Capacitor Design:
C-B and C-G Amplifiers
For C-B amplifier,
RiE R
in
R 6
For C-G amplifier,
RiS R
in
R 6
For coupling capacitor C1,
1
in
R I R
C
1
Jaeger/Blalock
7/1/03
Microelectronic Circuit Design
McGraw-Hill
Chap 14 - 15
Trang 16Coupling and Bypass Capacitor Design:
C-B and C-G Amplifiers
For C-B amplifier,
C3
RiC C
R out
R
For C-G amplifier,
3
RiD D
R out
R
C3
For coupling capacitor C3,
C 3 3 R 3 1 R out
Jaeger/Blalock
7/1/03
Microelectronic Circuit Design
McGraw-Hill
Chap 14 - 16
Trang 17Coupling and Bypass Capacitor Design:
C-B and C-G Amplifiers (contd.)
In this case, we can neglect impedances
of capacitors C1 and C3 , the find the equivalent resistance looking up into emitter or source of amplifier.
C
2 1
) 6
)(
1 (
2 1
R R
R CG eq
I R R o
r R
R
R CB eq
C2
2 1
q
R CB eq CG
C
,
1
2 R eq
C2
Jaeger/Blalock
7/1/03
Microelectronic Circuit Design
McGraw-Hill
Chap 14 - 17
Trang 18Coupling and Bypass Capacitor Design: C-B
and C-G Amplifiers (Example)
resistances for both C-E and C-S amplifiers.
For C-B amplifier:
Ω 100 Ω
102 kΩ 13
in R
kΩ 9 21 MΩ
93 3 kΩ
C
R out R
F 82 0 1 75.8nF
1
in
R I R C
C
R R
C
2 1
I R R o
r R R
Jaeger/Blalock
7/1/03
Microelectronic Circuit Design
McGraw-Hill
R R out
Chap 14 - 18
Trang 19Coupling and Bypass Capacitor Design: C-B and
C-G Amplifiers (Example contd.)
For C G amplifier:
kΩ 74 1 kΩ 04 2 kΩ 12
in R
kΩ 9 20 kΩ
410 kΩ
22
R R
R
F 42 0 1 42.6nF
1
R R
C
kΩ 9 20 kΩ
410 kΩ
out R
R I R in
pF 1800 pF
178 2
1
1
R R
C
3
1
out R R
C
2
Jaeger/Blalock
7/1/03
Microelectronic Circuit Design
McGraw-Hill
Chap 14 - 19
Trang 20End of Lecture 10