Electronic circuit for measuring periodic signal phase and frequency differences - has cyclic serial state machine, shift register, state identification logic and comparison logic

摘要

The electronic circuit measures phase and frequency differences of two periodic signals (FREQ1, FREQ2) using a comparator (1) with inputs for the periodic signals and a phase difference signal output. A cyclically and serially operating state machine (2) with at least two states has a clock input for the first signal (FREQ1) and an output at which the internal state appears as a periodic pulse sequence. A shift register (3) which forms an image of the state time shifted according to the phase difference has a clock input for the second signal. The internal state and the shifted state are compared by state identification logic (4, 5) and comparison logic (6) forming the comparator output (9). ADVANTAGE - Operates more rapidly than conventional phase-frequency comparators and reliably evaluates very small phase shifts.