Universal Current-Mode Gm-C Biquad

A universal current-mode biquad is described which is designed on the basis of well-known KHN (Kerwin, Huelsman, Newcomb) voltage-mode filter. In its most general form, the circuit consists of five operational transconductance amplifiers (OTAs) and of two grounded capacitors. The filter provides simultaneously three current outputs of HP, BP, and LP types into independent loads. The quality factor can be adjusted electronically independently on the natural frequency. Less rigorous rules of controlling the filter parameters can imply a reduction of number of OTAs to three or even two. The principle is verified by Spice simulation on the level of a CMOS structure of OTAs.