A tunable filter using amplifier pole
M.N.S. Swamy, K. Sankara Rao · Proceedings of the IEEE · 1975
A circuit consisting of two periodically operated switches, potentiometers, resistors, and compensated operational amplifiers, but not containing external capacitors, is proposed for the realization of a second-order bandpass and low-pass filter. The filter is electronically tunable and the natural frequency of the filter varies linearly with the width of the pulses controlling the FET switches.