CONTENTS

1. The How and Why of Feedback

2. The Effect of Feedback on Input Impedance

3. The Effect of Feedback on Phase Response, Frequency Response, and Stability

4. Multi-Loop and Multi-Stage Applications

5. Typical Feedback Applications

Preface:

Amplifier properties can be improved considerably by the deliberate use of inverse (aka: reverse) feedback to better response characteristics; to reduce hum, noise, or harmonic distortions; and to control gain.

These, and many other circuit uses, involve the feeding of part of the output voltage back to the grid circuit out of phase with the incoming signal.

Inverse feedback may involve voltage feedback, current feed back, or a combination of both (bridge feedback) . Each has its own effects on the amplifier input and output impedances and amplifier operation. This guide is designed to give an explanation of these and other important aspects of inverse feedback. The subject matter is organized to give a comprehensive review of the essential topics and it is assumed that the reader has a knowledge of basic electronic circuit principles.

Where essential, sufficient mathematics have been included to permit the advanced student, technician, or practicing engineer to follow the development of the fundamental concepts. Descriptive analyses are given of the effects and advantages of negative feedback; the types of inverse feedback; general and specific considerations pertaining to feedback effects on output and input impedances; voltage feedback considerations; phase relationships, phase response, frequency response, and stability as affected by feedback; feedback loops; inverse feedback used in push-pull amplifiers; and typical feedback applications.

Since the small scale of this guide precluded inclusion of all the many variations of circuit types, only a few of the more important common applications are given. These include the cathode follower, Williamson amplifier, avc, and a direct current vacuum tube voltmeter using inverse feedback.

Grateful acknowledgment is made to the staff of the New York Technical Institute for its assistance in the preparation of the manuscript of this guide.

- New York, N. Y., August 1956.

Also see: Electronic Experimenter's Manual (1959)

R-L-C Components Guide (1959)