Clock frequency monitoring device and clock frequency monitoring method

Abstract

[Problem] To monitor a frequency difference between an input clock and a synchronous clock synchronized with the input clock. [Solution] A clock frequency monitoring apparatus that monitors the frequency of an input clockincludes a phase comparatorthat compares a phase of a synchronous clockphase-synchronized with the input clockor a first frequency-divided clockobtained by frequency-dividing the synchronous clockwith the phase of the input clock, a filterthat low-pass filters an output signal of the phase comparator, an oscillatorthat generates the synchronous clockhaving a frequency corresponding to a control value from the filter, and a determinerthat determines that the frequency of the input clockis abnormal when the variation amplitude of the output signal of the filteris equal to or more than a predetermined range.