Device for sensing the period of a digitized signal including noise evaluation and averaging over a plurality of zero crossing

摘要

A real time sensor for signal periods includes a zero crossing sensor for sensing a period of a signal and a noise evaluation circuit. If the noise of the signal is smaller than a predetermined value, the output of the zero crossing sensor is averaged over a plurality of zero crossings to obtain the signal period. The zero crossing sensor uses the average voltage level of the sampled signal preceding the currently sampled signal as an assumed DC bias level, which is subtracted from the sampled voltage values to determine the points at which the sampled signal crosses an axis in order to measure the period of the signal, and the noise evaluation circuit operates by comparing the peak-to-peak value of the currently sampled signal with a reference peak-to-peak value.