Abstract: The inventive synchronization circuit accepts a reference input signal and produces a signal which is in both phase and frequency lock therewith. The reference signal is quadrature detected via a voltage controlled oscillator signal, a quadrature phase shifter and a pair of mixers. A frequency error signal is generated by processing the mixer outputs through a phase detector and integrator. A phase error signal is produced by extracting and combining the DC components of the signals at the mixer outputs. The frequency and phase error signals are summed to produce a control signal which is fed back to the voltage controlled oscillator, thus causing the oscillator signal to tend to lock in frequency and phase with the input reference signal.