Patent ID: 7460628

Claim:
A synchronous clock generation apparatus comprising: an A/D converter for converting an analog input signal, to which a synchronizing signal is added, into a digital signal using a synchronous clock, synchronized with the synchronizing signal, as a reference of sampling; a synchronizing signal separator circuit for separating the synchronizing signal from the digital signal; a pulse generation circuit for counting synchronous clocks up to a number which is previously set for the analog input signal to generate a synchronizing pulse signal; a multiplier for multiplying the synchronizing signal separated by the synchronizing signal separator circuit by the synchronizing pulse signal and outputting multiplication data; a low-pass filter for extracting a direct current component from the multiplication data and outputting the direct current component as correction data; a controller for setting a gain adjustment value, for gain adjustment which is performed on the correction data, based on the correction data, and outputting gain adjustment data indicating the gain adjustment value; a gain adjustment circuit for performing gain adjustment on the correction data based on the gain adjustment data and for outputting gain-adjusted correction data; and a voltage-controlled oscillator for generating a clock of a frequency according to the gain-adjusted correction data which is output from the gain adjustment circuit and outputting the clock as the synchronous clock, wherein the controller: captures the correction data output from the low-pass filter and stores a predetermined number of correction data counting from a latest correction data from among the captured correction data; subtracts a minimum value of the stored correction data from a maximum value of the stored correction data to calculate an amount of variation; and compares the amount of variation with a predetermined first threshold value and with a second threshold value smaller than the first threshold value, sets the gain adjustment value to a value larger than a current gain adjustment value when the amount of variation is larger than the first threshold value, and sets the gain adjustment value to a value smaller than the current gain adjustment value when the amount of variation is smaller than the second threshold value, without changing the gain adjustment value when the amount of variation is equal to or smaller than the first threshold value and is equal to or larger than the second threshold value.