Structure and Analysis of Properties of Basic Comb Filters for Automatic Systems

Abstract

The paper considers the issues of using comb filters (CF), known in radio engineering, as an alternative to continuous corrective filters, when they are implemented in controllers in automatic control systems. The convenience of their implementation in controllers is associated with the organization of a fixed number of sample passes in the processed signal. In this paper, the properties of two types of comb filters of the first order are highlighted and studied in detail: a high-frequency filter and a proportional (forming) filter. The characteristics of these filters are taken as a basis for the implementation of more complex characteristics of corrective devices in combination with numerical integration algorithms. The analysis of the properties of CF was carried out in the frequency domain. It is shown that the initial sections of the frequency characteristics of the CF at certain filter parameters coincide well with the continuous analogues of such devices. It is these areas of frequency characteristics, limited by the cutoff frequency of the open system, that determine the coincidence of static and dynamic properties of the synthesized system. It is shown that CF reduces on 30 % the level of the standard deviation (RMS) of uniformly distributed white noise at the filter output. The decrease in the level of RMS occurs due to the presence of periodically recurring dips in the amplitude-frequency response (frequency response) of filters forming a so-called comb. Due to the fact that the filters in question "cut out" harmonics in the output signal spectrum that are multiples of the inverse of the total duration of the transmitted reference intervals, then a special choice of this duration can not only reduce the level of the random signal at the CF output, but at the same time significantly reduce the level of regular interference, if it is present. Such filters can be simultaneously used as amplitude modulated signal demodulators.