Discrete-Analog Filters on Switchable Capacitors with a Summator of Input and Output Signals on a Differential Difference Operational Amplifier

Four new modifications of discrete analog filters (DAF) of second order low frequencies (LPF) on switched capacitors, which are protected by the authors of the article as objects of intellectual property, have been developed and studied. In the considered DAF family, unlike other known circuit solutions, summation of input and output signals is provided using a differential difference operational amplifier. As a result, the low-pass filter transmission coefficient in the passband does not depend on the passive elements of the circuit and is always equal to minus one. Buffer amplifiers in two DAF circuits are necessary to reduce the influence of switching circuits on transient processes. In the Micro-Cap environment, computer simulations of four modifications of DAFs were performed, showing that the proposed DAFs have the amplitude-frequency response of a low-pass filter. Sequences of pulses are given that should control four electronic keys, made, for example, on CMOS transistors. Graphs of transient processes of the DAF are shown for an input sinusoidal signal with an amplitude of 1V and a frequency of 1591 Hz, equal to the pole frequency at a switching frequency of electronic keys of 1 MHz. The DAF transmission coefficients for the input sinusoidal signal in different frequency ranges are determined. It has been established that with the selected parameters of the elements in the considered DAFs, which are low-pass filters, the input signal at a frequency of 159.10 kHz is attenuated by more than 60 dB.