Real time clock for GPS receivers
AssigneeseRide, Inc., Seiko Epson Corporation
InventorPaul W. McBurney
Life of this patent
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Abstract
A navigation-satellite receiver comprises a real-time clock that can be slaved to the highly accurate time base of the GPS system. During such times, the amount of correction and the operating temperature are both tracked. It is assumed the operating temperature will has the greatest influence of frequency errors later when the real-time clock cannot be slaved to the GPS time base. When the receiver is powered-down, the real time clock is nevertheless kept alive. Its free-running frequency is corrected for temperature. The next time the receiver is powered up, time accurate to better than one millisecond in a day can be obtained instantly for use in other receiver initialization procedures.
Claims4
A method for faster initialization of a navigation satellite receiver, the method comprising the steps of:
- maintaining sub-millisecond accurate time with a crystal oscillator;
- setting said crystal oscillator to atomic-standard accuracy when a navigation platform that includes it has acquired and is tracking satellite vehicles;
- measuring temperature of said crystal oscillator during periods said navigation platform is apparently powered-off;
- correcting a free running time of said crystal oscillator with data obtained in the step of measuring temperature when said navigation platform is not tracking satellite vehicles;
- and
- supplying sub-millisecond accurate time to said navigation platform prior to a next fix;
- wherein, the integer millisecond and z-count do not need to be determined by other methods.
Dependencies are inferred from the claim text.