CPC G01R 31/31726 (2013.01) [G06F 1/12 (2013.01); H03K 5/00006 (2013.01); H03K 5/1252 (2013.01); H03K 5/26 (2013.01)] | 6 Claims |
1. A clock frequency monitoring apparatus that recovers a synchronous clock synchronized with a first input clock and monitors a frequency of a second input clock that is to be frequency-synchronized with the first input clock, the clock frequency monitoring apparatus comprising:
a first phase comparator configured to compare a phase of the synchronous clock or a first frequency-divided clock obtained by frequency-dividing the synchronous clock with a phase of the first input clock;
a first filter configured to low-pass filter an output signal of the first phase comparator;
an oscillator configured to generate the synchronous clock having a frequency corresponding to an output signal of the first filter;
a second phase comparator configured to compare a phase of the synchronous clock or the first frequency-divided clock with a phase of the second input clock;
a second filter configured to low-pass filter an output signal of the second phase comparator; and
a determiner configured to determine that the frequency of the second input clock is abnormal when a variation amplitude of an output signal of the second filter is equal to or more than a predetermined range.
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