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MALVINO
Electronic
PRINCIPLES
SIXTH EDITION
Linear Op-Amp
Circuits
Chapter 20
ac coupled inverting amplifier
R2
C1
R1
C2
vin
-R2
AV =
R1
1
fc1 =
2pR1C1
f2 =
funity
R2
+1
R1
1
fc2 =
2pRLC2
RL
vout
Adjustable bandwidth
R2
R1
vout
vin
A
R
B=
-R2
R1
R1 R
R1 R + R2
f2 = Bfunity
f
ac coupled noninverting amplifier
C1
C2
vin
R3
R2
RL
Bdc = 1
1
fc3 =
2pR1C3
C3
R1
vout
JFET controlled inverter/noninverter
R
R
vin
0V
VGS(off)
R
vout
Adjustable gain of ± 1
R
R
vin
vout
Phase shifter
R’
R’
vout
vin
R
C
t
f = -2 arctan 2pRCf
f
Differential amplifier
R1
vin(CM)
R2
vin
vout
-R2
AV =
R1
vin(CM)
R2’
R1’
CMRR limiting factors
are the op amp itself and
the tolerance of the resistors.
Ideally:
R1 = R1’
R2 = R2’
DR
±2
< ACM < ±4 DR
R
R
Wheatstone bridge
+V
R1
R3
vout
R2
R4 Transducer
Wheatstone bridge
•
•
•
•
The differential output signal is small.
The common-mode output signal is large.
Differential amplifiers are a good match.
Transducers convert nonelectrical
quantities into an electrical quantity such
as resistance:
– examples: photoresistor, thermistor, strain
gage
Instrumentation amplifiers
• Differential amplifiers optimized for dc
performance
• Large differential voltage gain
• High CMRR
• Low input offsets
• Low temperature drift
• High input impedance
vin(CM)
Instrumentation amplifier
R
R
R1
vin
RG
R1
vin(CM)
-2R1
+1
AV =
RG
vout
R
R
DR
ACM = ±2
R
Monolithic instrumentation
amplifiers
• Use laser-trimmed resistors for high
performance.
• Resistor RG is external and is selected to
set the differential gain.
• Resistor RG can be split into two devices
for guard driving (bootstrapping the cable
shield to the common-mode potential).
Guard driving
RG
2
RG
2
Instrumentation
amplifier
vout
Guard voltage (common-mode voltage)
Summing amp with inverting
and noninverting inputs
v1
R1
RF
v2
vout
R2
v3
R3
R5
v4
R4
D/A converter
v3
v2
v1
v0
R
R
2R
4R
vout
8R
vout = -(v3 + 0.5v2 + 0.25v1 + 0.125v0)
N=4
Possible combinations = 2N = 24 = 16
1v
8 in
Unidirectional current booster
+VCC
vin
bdc = 100
741
R2
R1
RL
vout
Imax = bdcISC = 100(25 mA) = 2.5 A
Bidirectional current booster
R2
+VCC
R1
vin
RL
-VEE
vout
AGC circuit
R1
R5
vin
R2
vout
Voltage-controlled
resistance
+VAGC
R3
R4
-VEE
R6
As the signal level increases,
VAGC goes more positive.
As the JFET rds drops,
the input signal is attenuated.
Single-supply inverting amplifier
R2
C1
R1
+VCC
C2
vin
RL
R
C3
R
+VCC
2
vout