The voltage-controlled low-pass filter based on FPGA frequency measurement

This paper proposes a voltage-controlled selftracking filter system that can control the cut-off frequency of the filter by changing the external voltage. In the system, FPGA is used to measure frequency of the input signal, and D/A convertor is used to convert the measured frequency to voltage signal which will be input into the bi-quad loop filter as the external control terminal to control the cut-off frequency to track the input signal frequency changes automatically. Compared the voltage-controlled filter designed in this paper with other voltage-controlled filters, its cut-off frequency can dynamically adjust, and filtering speed is high, waveform is smooth and other features.