APPARATUS AND METHOD TO MAINTAIN STABLE CLOCKING

Both before and after a surprise clock stop, the apparatus and method of various embodiments supplies a stable and continuous clock to a memory module with a unique arrangement of circuit components, including a clock detector circuit, a clock-smoothing circuit, and one or more PLLs. Upon detection of a stopped host clock, a first PLL seamlessly switches to an alternate reference clock from an on-board crystal oscillator. A clock smoothing circuit allows the first PLL to maintain a steady phase and frequency without inducing glitches or period excursions greater than the natural jitter of the locked PLL; one or more optional downstream PLLs may drive additional clock domains.