The Application of Feedback to Wide-Band Output Amplifiers

A mathematical analysis is made of a typical two-stage output amplifier designed for the amplification of a wide range of frequencies incorporating feedback over the two stages. In wide-band amplifiers the use of output transformers is usually ruled out due to frequency limitations, and it is found that the time constant of the feedback circuit cannot be neglected. The effect of the feedback circuit is to give rise to peaks in the response curves at both the high- and low-frequency extremities of the band. The finite time constant of the feedback circuit greatly affects the latter. Design curves are included giving the response and phase shift for both the low- and high-frequency regions in terms of the feedback factor, the grid-coupling time constant, and the feedback-circuit time constant for the low-frequency region, and the feedback factor and the time constants for the shunting circuits in the plate circuits of both stages for the high-frequency region. Complete derivations of all formulas are given in the two appendixes.