A Study of the Transfer Function of Chopper Amplifiers

Abstract

The chopper amplifier is frequently used in several types of d.c and a.c amplifiers as well as in d.c servomechanisms employing a.c control elements. In this paper the transfer function of the chopper amplifier is derived for a sinusoidal input signal. The chopper amplifier has a chopper, or, a contact modulator at the input element of an a.c coupled amplifier to provide a means of converting d.c and low frequency signals to signals which lie within the pass band of the amplifier. Therefore, we first consider on the general analysis of the circuits containing a periodically operated switch such as a chopper. This analytical method is based on the theories of the Periodically Interrupted Electric Circuits and the complex Fourier series. The demodulation of the amplified signal is obtained by employing a synchronizing rectifier circuit, or a 2-phase induction motor at the output of the amplifier. In these systems we can easily derive the transfer function of some types of chopper amplifiers and of which the steady-state performance can be clearly stated in detail.