Abstract: Circuits such as Phase Lock Loops which use VCO's are affected by temperature and power supply variations which effect the performance of the circuit, particularly at high frequencies and low supply voltages. The present invention provides a variable delay circuit stage comprising one or more delay stages and an analogue multiplexer arranged to control the amount of delay introduced by the delay stages; a supply voltage pushing compensation circuit stage comprising a transconductance stage connected to the multiplexer and arranged to produce a compensating current upon deviation from nominal supply voltage which changes said delay; and a temperature pushing compensation circuit stage comprising a transconductance stage connected to the multiplexer and arranged to produce a compensating current upon deviation from nominal temperature which changes said delay.