Novel voltage-mode biquad without external passive elements

Abstract

This paper introduces a voltage-mode biquad filter using only active devices such as operational amplifiers and operational transconductance amplifiers (OTAs). The circuit configuration is obtained from Soderstrand's active-R state variable filter as a prototype. The proposed circuit can realize five different biquad transfer functions, and the circuit characteristics can be electronically tuned by adjusting the transconductance gains of the OTAs. An example is given, together with simulated results by PSPICE. The circuit configuration is very suitable for implementation in both bipolar and CMOS technologies.