Digitally controlled, conductance tunable active filters

Abstract

The use of digitally controlled variable conductances (DCVC's) to control the center frequency and selectivity of an active state variable filter is described theoretically and experimentally. Advantages of this approach are: zero sensitivity of selectivity with respect to the control conductances, excellent tuning linearity (1 percent over one decade) can be achieved with 1 percent part accuracies, a common digital control can be used to drive simple three-element variable conductances, and the input signal can be very low (about 0.5 mV) without any adverse effect on the tuning accuracy or linearity.