In one embodiment, a first circuit is configured to receive an input reference signal and a feedback signal, and present a reference clock signal based on a difference (e.g., phase difference) between the input reference signal and the feedback signal. The first circuit is further configured to present...http://www.google.com.hk/patents/US6674332?utm_source=gb-gplus-share專利 US6674332 - Robust clock circuit architecture
