Noninteracting electronically tunable CCII-based current-mode biquadratic filters

A complete state variable biquadratic filter built by CCIIs with variable current gain is presented and analysed. All the coefficients of the filter can be independently tuned through the variable current gain factors of the current conveyors. The authors propose fundamental techniques for the circuit implementation of the filter from the state variable block diagram. Design criteria to minimise the influence of the current conveyors' parasitic elements on the filter performance are presented. Based on the principles upon which the general biquadratic filter was constructed, a universal filter is proposed which implements the low-pass, high-pass, band-pass, band-reject and all-pass second order transfer functions simultaneously. Experimental measurements using Senani's current conveyor as well as PSPICE simulation using Surakampontorn's CCII were very close to theoretical values.