Clock retiming circuit

A method of operating a clock retiming circuit, the method comprising:

• operating the clock retiming circuit in a normal mode in response to an input clock being available to the clock retiming circuit, the normal mode comprising:
• i) outputting a reference clock, by a self-clock generation circuit, based on a frequency of the input clock;
• and
• ii) generating a retimed clock based on locking a frequency multiplying circuit to the reference clock, the retimed clock having a frequency that is based on a multiple of the reference clock;
• operating the clock retiming circuit in a retention mode in response to the input clock no longer being available to the clock retiming circuit, the retention mode having a low current period and a calibration period and comprising:
• i) instructing the self-clock generation circuit to not output the reference clock during the low current period and to output the reference clock during the calibration period;
• ii) calibrating the frequency multiplying circuit to the reference clock during the calibration period;
• and
• iii) storing, to non-transitory storage, calibration values from the frequency multiplying circuit locking to the reference clock during the calibration period.

A clock retiming circuit, comprising:

• non-transitory storage;
• mode means for operating the clock retiming circuit in a normal mode in response to an input clock being available to the clock retiming circuit and a retention mode in response to the input clock is no longer available to the clock retiming circuit;
• reference clock generating means for generating a reference clock having a frequency that is based on a frequency of the input clock;
• locking means for locking to the reference clock and for generating a retimed clock that has a frequency that is based on a multiple of the reference clock frequency;
• and
• calibration means for:
• i) instructing the reference clock generating means to not output the reference clock during the retention mode except during a calibration period of the retention mode;
• ii) calibrating the locking means to the reference clock during the calibration period;
• and
• iii) storing, into the non-transitory storage, calibration values from locking the locking means to the reference clock during the calibration period.