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7
Introduction to operational amplifiers
An operational amplifier is a high-gain DC-coupled amplifier with differential inputs and single-ended output. Op amps were originally developed
as vacuum-tube circuits to be used for analog computation. Nowadays they
are packaged as integrated circuits (ICs). Such devices can closely approximate the behavior of an ideal amplifier, and their use avoids the necessity of
coping with the messy internal details of amplifier circuitry. Thus, an IC
op amp is often the device of choice in scientific instrumentation. In this
chapter we will introduce the op amp and its most common applications.
Apparatus required
Breadboard, oscilloscope, multimeter, two 741 op amps, one further 741
(optional), one 100 !, three 10 k, two 100 k, one 1 M 14 W resistors, and
four more 10 k resistors (optional).
7.1 The 741 operational amplifier
The IC we shall be using is a general purpose op amp designated by the
number 741. The 741 is a very popular and successful design, useful for signals from DC to beyond audio frequency (though in recent years FET-input
op amps such as the LF411 have been gaining on the 741 in popularity).
It is available from most manufacturers of linear integrated circuits (chips
that produce an output proportional to their inputs, as opposed to digital
ICs, whose outputs have typically only two states).
Each manufacturer has a different system of nomenclature for ICs, e.g.
National Semiconductor calls the 741 an LM741, Fairchild a !A741, etc.,
but the 741s made by different manufacturers are all electrically compatible. To add complication, the 741 is available in various package styles
and is rated for use in various temperature ranges. The one we use is the
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