Frequency measurement circuit

Abstract

A frequency measurement circuit comprises a plurality of frequency measurement units 10, 20, K0 each of which counts a reference clock Cb during a counting period having a predetermined number of waves of an input signal Cin, each of the frequency measurement units counts the reference clock, with shifted counting periods, respectively. Moreover, an adder 14 is provided to add the counted numbers of the plurality of the frequency measurement units. By shift the counting periods, even if the phase of the input signal agrees with the phase of the reference clock at the time counting starts and at the time counting ends on a certain frequency measurement unit, there is scarcely any possibility of agreement of the phases on other frequency measurement units. Therefore, by utilization of the added number of counts, frequency can be measured with high accuracy. In addition, by making the counting periods being shifted with overlaping each other, extension of the measurement time is not required any longer.

Dependencies are inferred from the claim text.