| 摘要 |
<p>An optimum clock signal is selected from among a plurality of clock signals in a short time. A reference-clock counter (1a) counts clock pulses in an inputted reference clock signal (REF). A clock counter (1b) counts clock pulses in one of the plurality of clock signals which is selected by a selection unit (1e) and frequency-divided by a frequency divider (2). An instruction-signal output unit (1c) outputs a plurality of comparison-instruction signals during an interval in which a difference occurs between the counts of two of the plurality of clock signals having the closest frequencies. A comparison unit (1d) compares the count of the reference-clock counter (1a) and the count of the clock counter (1b). The selection unit (1e) selects a clock signal by a binary search according to the result of the comparison.</p> |
