A novel current-mode active-R biquad using differential-input differential-output operational amplifiers

This paper introduces a novel current-mode active-R biquadratic circuit employing two differential-input differential-output operational amplifiers (DIDO OAs). The circuit configuration has been obtained utilizing Soderstrand's voltage-mode state variable filter as a prototype. It is shown that the proposed circuit can realize five different biquadratic transfer functions simultaneously without changing the circuit topology. The parasitic effects of DIDO OAs on the circuit characteristics are also discussed using a general model of OA gain. An example is given together with simulated results by PSpice.