Patent ID: 6349391
Filing Date: 2002-02-19
Classification: G06F

Abstract:
A redundant clock system comprising:a first oscillator which produces first reference clock signals; a second oscillator which produces second reference clock signals; a third oscillator which produces third reference clock signals; a first multiplexer which receives the first, second and third reference clock signals from the first, second and third oscillators and which provides a designated one of the received reference clock signals as a selected reference clock signal; a second multiplexer which receives the first, second and third reference clock signals from the first, second and third oscillators and which provides a designated one of the received reference clock signals as a selected reference clock signal; a third multiplexer which receives the first, second and third reference clock signals from the first, second and third oscillators and which provides a designated one of the received reference clock signals as a selected reference clock signal; a first phase-locked loop (PLL) circuit coupled in a first feedback circuit in which the first PLL receives as reference input the selected reference clock signal provided by first multiplexer and receives as feedback input a first output clock signal; a second phase-locked loop (PLL,) circuit coupled in a second feedback circuit in which the second PLL receives as reference input the selected reference clock signal provided by the second multiplexer and which receives as feedback input the a second output clock signal; a third phase-locked loop (PLL) circuit coupled in a third feedback circuit in which the third PLL receives as reference input the selected reference clock signal provided by the third multiplexer and receives as feedback input a third output clock signal; and a reference clock designation unit which determines whether any one of the first, second or third reference clock signals has failed and which designates one of the two other reference clock signals in the event that one of the reference clock signals has failed.