TABLE OF CONTENTS Operational amplifiers, "op-amps" for short, are utilized in many areas of electronics, in filters, amplifiers, analog-to-digital and digital-to-analog converters, and in any circuit (below VHF frequencies) that requires gain and/or isolation. Op-amps have been the basic building block of analog instrumentation, and whether they are integrated into an application-specific integrated circuit (ASIC) or are used in stand-alone form they play a very important role in analog instrumentation.
An op-amp is basically a direct current (DC)-coupled, multistage, linear amplifier. It is not necessary to understand the operation of the internal components of an operational amplifier. There are just two rules, actually assumptions, that are necessary for proper understanding of operational amplifiers. But to use these assumptions, you must understand the characteristics of an operational amplifier.
It is a direct-current amplifier; in other words, when a DC level is placed on the input, an amplified proportional change will be obtained in the output.
Operational amplifiers have extremely high gain, above 100,000 when they are in the "open"-loop (no negative feedback) mode. This means that if you put a 1-microvolt change on the input, 0.1V change would appear in the output.
Op-amps use a differential input. They measure the difference in voltage between the two inputs, not any voltage that is common to both inputs.
Let's look at a discrete version of an operational amplifier. Though this is not a very good op-amp, it does illustrate the basic characteristics of op-amps.
Figure 16-1 illustrates the basic op-amp...
