Patent ID: 8446223

Claim:
A GPS device comprising: a real time clock (RTC) circuitry that generates RTC clock signals; a temperature compensated crystal oscillator (TCXO) that generates and sends TCXO clock signals to a GPS receiver; a ratio counter circuitry that receives both the RTC clock signals and the TCXO clock signals and determines a frequency ratio by comparing the RTC clock signals and the TCXO clock signals; and a computing device that receives the frequency ratio and estimates a current RTC frequency based on the received frequency ratio, the computing device being configured to calibrate an estimated RTC time being maintained at the RTC circuitry based on an estimated RTC frequency from a prior estimation, the current RTC frequency and an elapsed time of the RTC circuitry, wherein the RTC circuitry includes a RTC oscillator, a RTC counter, and a RTC alarm, the RTC oscillator being designed to generate the RTC clock signals, the RTC counter being designed to receive the RTC clock signals and generates an RTC counter value, the RTC alarm being designed to receive the RTC counter value and generates RTC alarm values based on a predetermined RTC counter value, wherein the ratio counter circuitry includes an acquisition clock (ACQCLK) counter that is electrically coupled to the TCXO and generates an ACQCLK counter value based on the TCXO clock signals, the ratio counter circuitry further including an edge aligned ratio counter (EARC) that receives the TCXO clock signals from the TCXO, the RTC clock signals from the RTC oscillator, and latches the RTC counter and the ACQCLK counter at a point in time where edges of the RTC clock signals and the TCXO clock signals are aligned, the EARC allowing the computing device to determine the difference in the number of counts from both the RTC counter and the ACQCLK counter as a ratio of count differences of nearly integer clock periods over a measurement period.