Building universal current-mode biquad active filters using CMOS linear transconductance elements

A new design approach for current-mode filters is presented. The realized circuits are composed only from CMOS transconductance elements and grounded capacitors. Direct block diagrams are employed to generate two universal biquad filter structures that are very suitable in building higher-order filters. The proposed circuits can simultaneously realize lowpass, bandpass and highpass filter behaviors or implement a general biquadratic transfer function, all at high impedance outputs. The circuits enjoy independent voltage control of parameters omega_o and Q. SPICE simulations demonstrate the validity of the approach and the good high-frequency performances of circuits.