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Keeping accurate time for a hybrid GPS receiver and mobile phone when powered off

  • US 7,598,909 B2
  • Filed: 09/11/2008
  • Issued: 10/06/2009
  • Est. Priority Date: 09/04/2003
  • Status: Expired due to Fees
First Claim
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1. An apparatus comprising:

  • a global position system (GPS) navigation receiver part including;

    a GPS radio frequency (RF)-receiver, a GPS oscillator that provides a reference frequency to the GPS RF receiver, a low-frequency oscillator, a clock selector to select between the GPS oscillator and the low-frequency oscillator, a GPS-chip including a GPS digital processor for acquiring and tracking GPS satellite signals from the GPS RF receiver when connected by the clock selector to the GPS oscillator, and a numeric controlled oscillator (NCO) with a frequency output that can be compensated with GPS satellite time standard information derived during the tracking of said GPS satellites;

    a communications transceiver part having no crystal oscillator of its own by depending on frequency references provided over said NCO output, and including;

    a cellphone transceiver, a digital signal processor connected to the cellphone transceiver, a phone host CPU, a clock frequency divider connected to receive GPS-corrected frequencies from said NCO output instead of a communications VCO-crystal, and a voltage controlled oscillator (VCO) that receives a reference clock frequency output from the divider, and that provides a programmable synthesized reference frequency for the cellphone transceiver that has been compensated to GPS satellite time standards by values loadable into said NCO;

    wherein, at turn-on, the GPS-chip loads a default value for the phone host processor CPU into said NCO that will produce a startup processor clock, and thereafter a particular NCO output frequency can be requested by loading other values into said NCO; and

    wherein, the GPS receiver part provides for the compensation of NCO output frequencies by computing any error in the GPS oscillator to provide a compensated frequency to the VCO.

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