The Flexible Functionality of Op-Amps

Picture of 8 black op-amps on a wooden surface

Before the modern digital technology we use in computers today, electronic computations were conducted by utilizing both voltages and currents as representations of numerical values. This process needed circuitry capable of carrying out a wide range of analog signal processing tasks, which led to the use of operational amplifiers (often referred to as op-amps). The engineering concept of negative feedback, which forms the basis of practically all automatic control procedures, holds the key to the utility of these tiny circuits.

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Amplifier Types

There are many different types of amplifiers. The first type to be discussed is operational amplifiers. These are also known as op-amps. Op-amps are integrated circuits where the chip contains the transistors of the stages and resistors and capacitors as well. An op-amp is a differential amplifier on a chip, in which most points in the circuit are accessible through terminal connections. The terminals can be linked, so different parts or all of the differential amplifier can be used for different functions. Since both stages of the differential amplifier produce opposite outputs, either stage can be used as an inverting or noninverting amplifier. Since the first stage feeds the second stage as an emitter follower, the emitter follower output can be used.  It can be used with one or two inputs, or one or two differential or emitter-follower outputs. If external resistors for feedback or stabilization are added, the op-amp can also function as oscillators, gates, counters, and various others. Op-amps are used extensively in digital meters.

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Digital Circuits

Input Networks and Amplifiers

The input network and amplifier perform the same functions as they do for the electronic analog meter. The input network presents a high resistance (11 megohms) to the circuit under test to keep from loading it down; it also attenuates the input voltage with the range switch setting to keep the test signal at the input of the amplifier under 1 volt. Although identical input and amplifier circuits can be used for both digital and analog meters, the example we are using demonstrates the use of an amplifier that can take up to 1 volt of input, and the ranges vary from 2 volts to 2000 volts, in multiplier ranges of 2, 20, 200, and 2000 volts. Since digital measurements use ten digits (0- 9), the counters, and especially the pulse generators deal in multiples of ten for convenience. The follower and amplifier circuits are both op-amps connected to accomplish their functions.

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