The Second Order Low Pass Filters on the Switched Capacitors with Signal Adder Based on Differential Difference Amplifier

Three new modifications of the second-order discrete-analog low-pass filters on the switched capacitors are developed. In these circuits, the summation of the input signal of the second-order discrete-analog low-pass filters on the switched capacitors and the output signal of the filter integrator, made on the classical operational amplifier, is performed using a differential difference amplifier with two input ports. This provides a unity gain of the second-order discrete-analog low-pass filters on the switched capacitors at low frequency. Computer simulation of the suggested discrete analog low-pass filter modifications was performed in the Micro-Cap software, where use standard analog elements models and models of AD830 differential difference operational amplifiers and OP37 classical operational amplifiers. The simulation results demonstrate that in the first two discrete-analog low-pass filter circuits considered, a single element tuning of the pole frequency is possible at a fixed switching frequency of the CMOS keys. The third discrete analog low-pass filter circuit is characterized by the higher values of the initial Q factor at the same capacitance ratio of the switched capacitors.