A versatile current-mode biquad using operational amplifiers

A versatile current-mode biquad filter using three operational amplifiers and 9 passive elements is proposed. By the suitable choice of the output branch, lowpass, bandpass, highpass, bandstop and allpass transfer functions are realized simultaneously without changing the circuit configuration and elements. Two circuits, one is for low frequency application and the other for high frequency, are proposed. The center frequency, quality factor and gain constants of the circuit can be tuned independently. Simulated results will show that the circuits work successfully.