| 摘要 |
A frequency comparator for comparing the frequency of a predetermined clock signal with the clock frequency of a non-return-to-zero (NRZ) signal having a detector circuit for detecting a data change of the NRZ signal in an interval of one time period of the clock signal, and a comparator circuit for generating a comparison result only when a data change is detected by the detector. The detector includes a data change circuit for detecting a data change of the NRZ signal and a change position detector for detecting a data change position of the NRZ signal in a time period of the clock signal CLK by taking in the logic of a clock signal and an auxiliary clock signal having the phase delayed 90 degrees from that of the clock signal when a data change of the NRZ signal is detected. The comparator circuit has a setting circuit for setting a reference point for detecting the time period subsequent to the clock signal to generate the comparison result based on the reference point set by the setting circuit.
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