An oscillator, including amplifier circuitry and resonant circuitry, for providing an oscillation signal with a controllable frequency while maintaining a substantially constant steady state magnitude. Controllable reactive circuitry, included as part of the amplifier circuitry, has a reactance which can be controlled such that the resistive components of the amplifier circuitry and resonant circuitry impedances remain substantially equal. When in the form of serially coupled, controllable capacitances, the controllable reactive circuitry is controlled such that a ratio of changes in the controllable capacitances is approximately equal to a negative ratio of the capacitance values.