Suppression of periodic interference in the input signal of a precision pulse width modulator using an S&H circuit and weighted averaging

Abstract

The results of theoretical and simulation studies concerning the occurrence of nonlinear distortions and the reduction of their impact during pulse width modulation of variable measurement signals are presented in this article. It has been shown that when input signal is variable, the classic PWM method may be inaccurate due to addition intense modulation distortion, which may be caused by noise or interference (e.g., power lines). The level of these distortions is dependent on the level and speed of the input signal changes, as well as the modulation frequency. In order to reduce the impact of those distortions, the use of the sampling and holding circuit at the input of the pulse width modulator, and weight averaging of the output pulses have been proposed. The effectiveness of the suppression of the periodic interferences in both narrow and wide bands was investigated through theoretical research and through simulations conducted in the LTSpice software using uniform, triangular, Hamming, and Blackman weighting functions for the classic PWM, and for one with the addition of the S&H circuit.