Frequency Response of Feedback Relay Amplifiers

The frequency response of feedback relay amplifiers is analysed by the dual-input describing-function method. At low signal frequencies, the amplifier behaves like a saturating linear amplifier. This picture is modified at higher frequencies, owing to synchronous effects, and it is difficult to achieve satisfactory operation when the ratio of the input-signal frequency to the periodic excitation frequency is appreciable. To eliminate synchronous effects within the signal band, restrictions must be imposed on the forward linear-transfer function. The theory is compared with an experimental example.