Failsafe clock product using frequency estimation

A clock product comprising:

• a first select circuit configured to provide a first active clock signal selected from a plurality of independent clock signals in response to a first control signal;
• a first control loop configured to generate a first output clock signal by locking to the first active clock signal;
• and
• an estimator configured to generate frequency metrics for the plurality of independent clock signals using a reference clock signal;
• and
• a control circuit configured to generate the first control signal based on the frequency metrics,
• wherein for each input clock signal of the plurality of independent clock signals, the frequency metrics include a current average frequency count, a prior average frequency count, a standard deviation of prior average frequency counts, and a multiplicative constant corresponding to a number of samples used to determine the current average frequency count, prior average frequency count, and standard deviation.

An apparatus comprising:

• means for generating a quality determination for a reference clock signal based on frequency metrics for a plurality of independent clock signals, the frequency metrics being generated using the reference clock signal;
• and
• means for generating an output clock signal by locking to an active clock signal selected from the plurality of independent clock signals in response to the quality determination satisfying a predetermined quality metric,
• wherein for each input clock signal of the plurality of independent clock signals, the frequency metrics include a current average frequency count, a prior average frequency count, and a standard deviation of prior average frequency counts and a multiplicative constant corresponding to a number of samples used to determine the current average frequency count, prior average frequency count, and standard deviation.