The Second-Order Discrete-Analog Filter on Three Switched Capacitors and Tuning of Pole Frequency by Multiplying Digital-to-Analog Converter

A discrete-analog filter of the second order with a multiplying digital-to-analog converter, three frequency-dependent capacitors and three-phase control of electronic keys, which has four outputs and realizes the characteristics of low-pass filter (LPF), band-pass filter (BPF), high-pass filter (HPF) and rejecting filter (NPF), that is the subject of the research, is developed. The results of modeling of the proposed filter circuit in Micro-Cap environment at different outputs at input signal frequencies differing by several orders of magnitude are presented. It is established that the pole frequency in the discrete-analog filter circuit can be changed by changing the transmission coefficient of the digital-to-analog converter by changing the binary code supplied to its control inputs, while all other circuit parameters remain unchanged - transmission coefficients and pole attenuation. It is shown that the frequency of the pole depends on the capacitance of the capacitor C 2 and the transmission ratio of the digital-to-analog converter <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$K_{d a c}\left(K_{f}\right)$</tex>, the transmission ratio of which can be changed by changing the binary digital code <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$K_{f}$</tex> supplied to its control inputs, and the other parameters of the filter link do not depend on them, so by changing the capacitance of this capacitor or the transmission ratio of the digital-to-analog converter the frequency of the pole can be tuned in a wide range while keeping the other parameters.