Abstract: A VCO and filter each include a variable transconductance amplifier as a resistive element. The same control bias current is supplied to the variable transconductance amplifier of both the oscillator and filter. This control bias current may be externally supplied, or may be generated on-chip from a thermal RC network formed from base-emitter junctions of bipolar transistors arrayed in single crystal silicon about a heat source. Application of a clock signal from the VCO to the heat source generates a heat pulse which propagates across the arrayed transistors. The resulting change in temperature produces a change in Vbe of the arrayed transistors. The phase shift between the original clock signal and the changed Vbe is determined solely by the time constant &tgr; of the particular thermal RC network. This time constant is a function of the inherent stable thermal resistance and capacitance of the single crystal silicon, and of the location and relative spacing of the arrayed transistors.