Abstract: A digital phase detector includes a hard limiter which transforms an incoming signal of known frequency into a binary signal at the same frequency. A reference generator produces two binary references at the signal frequency, one reference shifted 90.degree. in phase with respect to the other. The binary signal is exclusive-ORed with each reference and the exclusive-OR outputs therefrom control two counters, the counters thereby registering counts analogous to trigonometric functions of the signal phase angle. A phase modulated clock drives the counters, the phase modulation feature permitting a correction factor to be incorporated in order to cancel the error introduced by the quantized nature of the digital computations involved.