IMPLEMENTATION OF AN ACTIVE-R FILTER BUILDING-BLOCK IN SEMICUSTOM VLSI

A universal active-R building block was successfully designed and impl emented using semi-custom VLSI (analogue gate-array) technology. The c ircuit makes use of the inherent charge storage in the low-frequency P NP transistors buffered by high-frequency NPN transistors which elimin ates the need for capacitors and results in active-R filters that appr oximate the desired frequency response at high frequencies better than active-RC filters. A two-chip chip set is proposed for use as a pract ical building block for the p-plane design approach to active-R filter s. The first chip contains two p-plane integrators which can be used t o design any active-R filter. The second chip contains the parameter-c ompensation circuit which monitors the circuit on the first chip and u ses this information to adjust the bias point on the integrator transi stors in order to maintain constant integrator characteristics over a wide range of conditions including process variations, bias conditions , and temperature changes. As a result, the complete active-R filter m aintains its characteristics better than active-RC filters over simila r variations.