Synthesis of biquadratic filters from current conveyors

This paper describes a circuit configuration for a biquad filter which utilizes the second-generation current conveyors (CC II) and is capable of synthesizing an arbitrary second-order transfer function. The circuit is composed of a subblock circuit with two positive CC IIs and a differential input circuit with two positive CC IIs. The subblock circuit realizes a lowpass, high-pass, and bandpass filter. Combining this with the differential input circuit produces an all-pass and notch filter. Each filter has a high input impedance because its input is the Y terminal of the CC II and can be cascaded without a buffer. The quality factor Q of the filter is determined by a ratio of passive elements, and its sensitivity to the passive element values is less than 0.5. These characteristics make the filters suitable for monolithic IC implementations. The effects of CC IIs voltage error ϵv and current error ϵi on the filter characteristics were studied. It was found that the center frequency ωo is independent of these errors, Q is affected only by ϵi, and the gain factor is a function of both ϵv and ϵi. Each filter was prototyped and was verified to operate as predicted.