Patent ID: 6965659

Claim:
A device for detecting a period of an input signal comprising: a count value setting portion for setting a reference clock to be counted by n times, where n is an integer; an analog-to-digital (A/D) converter for sampling an analog input signal at each period of the reference clock, and converting the input signal into digital values having positive and negative symbols; a zero cross point detecting portion for detecting a symbol change of the digital values output from the A/D converter, and generating a zero cross point detecting signal; an arithmetic processing unit for dividing a sampling interval between two sampling points having a zero cross point therein, by a preset value which is set in the count value setting portion, predicting a zero cross point sector based on the digital values of the two sampling points, and calculating count values of the reference clock in accordance with the preset value and the predicted zero cross point sector; a counter for accumulating the count values of the reference clock which are calculated in the arithmetic processing unit, until the symbols of the digital values are changed; and a period value calculating portion for dividing the accumulated count values in the counter by the preset value which is set in the count value setting portion, and calculating periods of the input signal.