MALVINO Electronic PRINCIPLES SIXTH EDITION

Linear Op-Amp Circuits Chapter 20

ac coupled inverting amplifier vin R2 R1 +1 funity f2 = AV = -R2 R1 RL vout fc1 = 2pR1C1 1 fc2 = 2pRLC2 1

Adjustable bandwidth R2 R1 vout vin R1 R B = A R R1 R + R2 -R2 R1 f2 = Bfunity f

ac coupled noninverting amplifier vin R3 R2 RL vout Bdc = 1 R1 fc3 = 2pR1C3 1 C3

JFET controlled inverter/noninverter vout R vin 0 V VGS(off)

Adjustable gain of ± 1 R R vout vin

Phase shifter R’ R’ vout vin R C t f = -2 arctan 2pRCf f

are the op amp itself and the tolerance of the resistors. Differential amplifier R1 R2 vin(CM) AV = -R2 R1 vin vout vin(CM) R1’ R2’ Ideally: R1 = R1’ R2 = R2’ CMRR limiting factors are the op amp itself and the tolerance of the resistors. ±2 < ACM < ±4 DR R

Wheatstone bridge +V R1 R3 vout Transducer R2 R4

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

Instrumentation amplifier vin(CM) R R R1 vin RG vout R1 R R vin(CM) AV = -2R1 RG +1 ±2 DR R ACM =

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 voltage (common-mode voltage) Guard driving RG 2 Instrumentation amplifier vout RG 2 Guard voltage (common-mode voltage)

Summing amp with inverting and noninverting inputs RF R1 v1 v2 R2 vout R3 v3 R5 v4 R4

D/A converter R R v3 2R 1 vin v2 8 vout 4R v1 8R v0 vout = -(v3 + 0.5v2 + 0.25v1 + 0.125v0) Possible combinations = 2N = 24 = 16

Unidirectional current booster +VCC vin 741 bdc = 100 R2 vout R1 RL Imax = bdcISC = 100(25 mA) = 2.5 A

Bidirectional current booster +VCC R1 vin RL vout -VEE

AGC circuit R5 R1 R2 vin vout Voltage-controlled resistance R6 +VAGC As the signal level increases, VAGC goes more positive. As the JFET rds drops, the input signal is attenuated. R3 R4 -VEE

Single-supply inverting amplifier +VCC C1 R1 C2 vin RL vout R C3 R +VCC 2