US Patent 8937496 Clock monitor

A clock monitoring circuit is disclosed. The clock monitoring circuit is configured to receive first and second clock signals generated in respective clock domains. The clock monitoring circuit includes a first counter configured to count clock cycles of the first clock signal for a first period of time delineated by clock cycles of the second clock signal. The first counter outputs a count value indicating the number of counted clock cycles. The clock monitoring circuit also includes a threshold comparator circuit configured to generate an error signal in response to expiration of the first period of time and the first count value output by the first counter falling outside of an expected range.