Method of interruption-free switching between two precision oscillator clock-pulse generators for computer systems, involves tracking both clock-signals in order to establish exact time at which phase coincidence of the signals occurs

摘要

Networked computer systems, particularly high-end systems with a number of CECs distributed into several clusters, require perfect phase coincidence of the clock-signals, owing to the sensitivity of the phase-locked loop (PLL) circuits operating at several hundred MHz, with a accuracy of about 20 pico-seconds (ps) required in the phase coincidence. Both clock-phase signals need to be monitored in order to find the exact time at which phase coincidence of the signals occurs, and then to switch over from one clock-source to the other. The signal phases are not compared directly, but an auxiliary signal, or phase-detector signal, is generated from both clock-signals and is used to find the required time-point having the necessary characteristics of the time-dependent phase displacement or shift.