Patent ID: 7592951
Filing Date: 2009-09-22
Classification: G01S

Abstract:
1. A method for limiting the number of crystals in a combination of a navigation receiver and cellphone, comprising: generating reference frequencies from one master clock crystal reference oscillator for general use by each of a collocated navigation receiver, mobile telephone and host CPU, the general use including controlling a master clock to maintain generated Global Positioning System (GPS) system time; stopping the generating of said reference frequencies from said master clock crystal reference oscillator when a user inputs a power-off command; restarting the generating of said reference frequencies from said master clock crystal reference oscillator when a user inputs a power-restart command; continuously operating a real-time clock (RTC) and crystal at a frequency orders of magnitude less than said one master clock crystal reference oscillator, and said RTC thereby consumes orders of magnitude less operating power than said one master clock crystal reference oscillator; regenerating GPS system time from said RTC when said user inputs said power restart command; and using a software controlled crystal oscillator (SCXO) to receive current time information derived from RTC and previous samples of accurate time derived from GPS receiver, and current temperature information (T), and then to provide corrections to said master clock crystal reference oscillator during a user initiated power restart; wherein, said crystals are the only ones included in the whole combination of said collocated navigation receiver, mobile telephone and host CPU; and wherein, continuously operating said RTC during power down substantially improves any frequency uncertainty that would otherwise prevail for said one master clock crystal reference oscillator from a power restart.