Digitally controlled, conductance tunable active filters

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.