ABSTRACT
This chapter discusses the effects of feedback on amplifier impedance and gain and obtain some useful relations among the return difference, the null return difference, and impedance functions in general. The return difference for x when the input port is short circuited or open circuited is relatively simple to compute because shorting out or opening a terminal pair frequently breaks the feedback loop. One of the most important effects of negative feedback is its ability to make an amplifier less sensitive to the variations of its parameters because of aging, temperature variations, or other environment changes. A singleloop feedback amplifier composed of a cascade of common-emitter stages with a passive network providing the desired feedback fulfills the requirements. In the case of a single-loop feedback amplifier, it is usually possible to choose a terminal pair so that either the numerator or the denominator on the righthand side of is unity.
