TABLE OF CONTENTS Walt Jung
The term "composite op amp" can mean a variety of things. In the most general sense of the word, any additional circuitry at either the input or the output of an op amp could make the combination of what is termed a composite amplifier. This can be a valuable thing, as often such enhancements allow new performance levels to be realized from the resultant amplifier.
Some straightforward op amp performance enhancements of this type of have already been treated elsewhere in this book. For example, within the "Buffer Amplifiers" section of this chapter, as well as some of the specialized buffers in the "Audio" section of this chapter are found what could be termed composite op amps. In these examples, a standard output stage buffering design step is to utilize a unity-gain buffer, running on the same supplies as the op amp being buffered. So long as this buffer has sufficient bandwidth, this is an easy and straightforward step insert the buffer between the op amp and the load, connect the feedback around the op amp plus buffer, and that's it.
A very useful means of increasing op amp performance can be obtained by blending the performance advantages of two ICs, or a standard op amp IC and discrete transistors. Such a combination is known as a composite amplifier. In special situations, a well-designed composite amp can often outperform standard op amps. The reason this is true is that the composite amplifier can be...
