VLSI design of active filters

A good biquad filter, from practical point of view, should be capable of controlling the poles and zeros independently. In other words, it should be able to control pole frequency and pole Q and the type of generic filter independently. This calls for the control over the numerator and denominator coefficients by independent elements. Such circuits can then be programmed digitally. From economic fabrication point of view the biquad should use as small silicon area on the chip as possible. This is possible by reducing the total capacitance and/or resistance and number of OAs and time-multiplexing the components. The aim of this paper is to present two such biquads which meet the above requirements.