A FAMILY OF SECOND-ORDER ACTIVE RC FILTERS (LPF, HPF, BPF) WITH INDEPENDENT ADJUSTMENT OF THE MAIN PARAMETERS

Abstract

A bank of circuit design solutions for active RC filters of the second order is considered - a
low-pass filter, a high-pass filter and band-pass filters, in which independent tuning of the main
parameters - the pole frequency, the quality factor of the pole and the transmission coefficient is
provided. From these positions, the requirements for three special transfer functions of a multipole
frequency-setting RC circuit, which contains two resistors and two capacitors, are formulated.
By choosing the coefficients of the numerator of the first transfer function, the type of the required
filter (LPF, HPF, BPF) is implemented. The coefficients of the second transfer function are chosen
so that they affect only the frequency of the pole. It should be noted that, depending on the set of
coefficients of the transfer function numerator polynomial, the developed circuits have the property
of lowering the pole frequency or increasing the pole frequency. In this case, the choice of parameters
of the third transfer function provides the necessary attenuation of the pole. Using the
The introduction describes a generalized architecture of second-order active RC filters, which
allows implementing an algorithm for step-by-step tuning of the main parameters and can be used
as the basis for the synthesis of many other modifications of active RC filters. For correct independent
adjustment, the following sequence must be observed: the frequency of the pole, the second
stage is the adjustment of the quality factor of the pole, and the third stage is the scaling
factor. The stages of synthesis of this class of active RC filters are considered, the coefficients of
the transfer functions of the presented circuits of 12 band-pass filters, a high-pass filter and a lowpass
filter, confirmed by 14 patents of the Russian Federation, are given.