A novel circuit for precise phase detection between two signals with the same frequency is presented. It is shown how the non-idealities in conventional phase detectors give rise to nonlinearities in the average voltage vs. phase characteristic. The proposed circuit makes use of a pair of XNOR-type phase detectors, to which signal and quadrature reference clocks are applied. A decision circuit then selects which of the two XNORs is used for the output, which guarantees that the circuit will be well within its linear region.