High accuracy low power gps time source

Abstract

A global positioning system (GPS) receiver and high accuracy low power time source (HAL) are disclosed. The HAL provides a time source having an accuracy which is high enough for the receiver to achieve fast direct Y-code acquisition. The HAL includes an oscillator adapted to provide an uncompensated frequency signal at a desired frequency. Frequency conversion circuitry receives the uncompensated frequency signal and a control signal as inputs, and provides as an output a compensated frequency signal having an average compensated frequency which is closer to the desired frequency than is the average uncompensated frequency. A temperature sensor provides an output indicative of a temperature of the oscillator. Frequency error determining circuitry determines an error value, as a function of the temperature sensor output, which is indicative of a quantity of frequency error over time in the uncompensated frequency signal. The frequency error determining circuitry generates the control signal as a function of the determined quantity of frequency error in the uncompensated frequency signal. A counter receives the compensated frequency signal from the frequency conversion circuitry and provides as an output a digital representation of a time period based upon the compensated frequency signal.