Electronically tunable current-mode biquadratic filter and four-phase quadrature oscillator

This paper presents a current-mode biquadratic filter based on ZC-CFTAs. It employs only three ZC-CFTAs, one resistor and two grounded capacitors. It can simultaneously realize not only highpass and lowpass filtering functions but also two different forms of bandpass ones; one has a pass-band gain of Q, the other, a pass-band gain of unity. Its ωo and Q can be tuned orthogonally through adjusting bias currents of ZC-CFTAs. Moreover, the proposed circuit can also be modified to be a current controlled four-phase quadrature oscillator with small distortion. Non-ideal analysis and sensitivity analysis are provided. The results of circuit simulations are in agreement with theory.