| 摘要 |
PROBLEM TO BE SOLVED: To obtain a frequency measurement circuit of an ultra-wide band for coping with a specific input clock frequency range by preparing several types of reference clocks and selecting a reference clock and a measurement method according to preliminary measurement. SOLUTION: A reference clock generation circuit 1 generates several types of highly stable reference clocks that are to be the reference of frequency measurement. A reference clock selector 2 selects a reference clock when measuring a frequency. A reference clock counter 3 counts the number of pulses of the reference clock. Then, a clock counter 4 to be measured counts the number of pulses of an input clock pulse signal to be measured. A control part 5 gives the timing for starting and ending measurement to both clock counters 3 and 4, selects the reference clock on preliminary measurement, and judges the measurement method, and calculates the frequency of the input clock pulse signal to be measured after the frequency measurement operation is completed, thus performing an efficient measurement with a measurement error within±0.01% for the frequency of a wide range of input clock pulse signal to be measured, for example, 2Hz-1MHz.
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