A voltage controlled filter circuit that uses operational transconductance amplifiers, or OTAs, as processing and control elements. The circuit relies on a property of the OTA, which is that as its gain factor changes, its signal input impedance also changes, which (somewhat of an over-simplification) allows the OTA to be used as, in effect, a voltage controlled resistor. This is used as the resistance in a basic R-C filter circuit, and so by using a control voltage to vary the gain of the OTA, the R-C time constant and hence the cutoff frequency can be varied.