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| SEC. 20-1 INVERTINGAMPLIFIER
CIRCUITS Inverting-amplifier circuits discussed in this section included a high-impedance probe (X10 and X1), an ac-coupled amplifier, and an adjustable-bandwidth circuit. SEC. 20-2 NONINVERTINGAMPLIFIER CIRCUITS Noninverting-amplifier circuits discussed in this section included an ac-coupled amplifier, an audio distribution amplifier, a JFET-switched amplifier, and a voltage reference. SEC. 20-3 INVERTER/ NONINVERTER CIRCUITS The circuits discussed in this section are the switchable inverter/noninverter, the JFET-controlled switchable inverter, the sign changer, the adjustable and reversible gain circuit, and the phase shifter. SEC. 20-4 DIFFERENTIAL AMPLIFIERS Two factors determine the overall CMRR of a differential amplifier: the CMRR of each op amp and the CMRR of the matched resistors. The input signal is usually a small differential voltage and a large common-mode voltage coming from a Wheatstone bridge. SEC. 20-5 INSTRUMENTATION AMPLIFIERS An instrumentation amplifier is a differential amplifier optimized for large voltage gain, high CMRR, low input offsets, low-temperature drift, and high input impedance. Instrumentation amplifiers can be built with the classic three op-amp circuit, using precision op amps, or with an integrated instrumentation amplifier. SEC. 20-6 SUMMING AMPLIFIER CIRCUITS The topics discussed in this section were the subtracter, summing on both inputs, the averager, and the D/A converter. The D/A converter is used in digital multimeters to measure voltages, currents, and resistances. SEC. 20-7 CURRENT BOOSTERS When the short-circuit output current of an op amp is too low, one solution is to use a current booster on the output side of the circuit. Typically, the current booster is a transistor whose base current is supplied by the op amp. Because of the transistor current gain, the short-circuit output current is increased by the β factor. SEC. 20-8 VOLTAGECONTROLLED CURRENT SOURCES We can build current sources that are controlled by an input voltage. The loads may be floating or grounded. The load currents may be unidirectional or bidirectional. The Howland current source is a bidirectional voltage-controlled current source. SEC. 20-9 AUTOMATIC GAIN CONTROL In many applications we want the voltage gain of a system to change automatically as needed to maintain an almost constant output voltage. In radio and television receivers, AGC prevents sudden and large changes in the volume of the sound out of the speakers. SEC. 20-10 SINGLE-SUPPLY OPERATION Although op amps normally use dual supplies, there are applications for which only a single supply is preferred. When accoupled amplifiers are needed, single-supply amplifiers are easily implemented by biasing the nonsignal side of the op amp to half the positive supply voltage. Some op amps are optimized for single-supply operation. |