An oscillator circuit providing quadrature outputs and enabling instantaneous control over phase, frequency and amplitude of the output waveforms is disclosed. In one embodiment, the oscillator circuit comprises an oscillation loop, at least one capacitor switching circuit coupled to the oscillation loop, and a synchronization signal having an output coupled to the at least one capacitor switching circuit. The synchronization signal may be derived internally from the oscillation loop or externally from an external oscillator.