HIGH-RELIABILITY HOLDOVER METHOD AND TOPOLOGIES

摘要

System and methods for a clock system disciplined to an external reference. In one embodiment, the clock includes a flywheel oscillator controlled by the external reference and a free running holdover oscillator. The holdover oscillator provides increased accuracy during periods of holdover when the external reference is not available. In a further embodiment, the flywheel oscillator is additionally controlled by a phase-locked loop with the holdover oscillator frequency as input, and a control switch for switching the flywheel oscillator to analog control if the phase-locked loop exhibits a fault.

主权项

1. A disciplined clock system comprising:
a flywheel oscillator receiving a tuning voltage and outputting a flywheel oscillator frequency to a first counter responsively outputting a first counter time signal, wherein the flywheel oscillator frequency is controlled by the tuning voltage; a holdover oscillator outputting a holdover oscillator frequency to a second counter responsively outputting a second counter time signal; a time comparator module communicatively coupled to an external reference, the first counter, and the second counter, the time comparator module configured to perform the steps of:
receive the first counter time signal, the second counter time signal, and an external reference time signal from the external reference;compare the external reference time signal, the first counter time signal and the second counter time signal, wherein a difference between two signals is a time error value; andresponsively output a time error output including at least one time error value; a clock control module coupled to the time comparator module and receiving the time error output and performance data from at least one of the holdover oscillator and at least one sensor, and responsively outputting a voltage control; and a digital-to-analog converter coupled to the clock control module and the flywheel oscillator, the digital-to-analog converter receiving the voltage control and responsively outputting the tuning voltage to the flywheel oscillator; wherein the time error output is used by the clock control module to determine the voltage control when the external reference time signal is reliable; and wherein the time error output and the performance data are used by the clock control module to determine the voltage control when the external reference time signal is unreliable.