High accuracy low power GPS time source
First Claim
1. A global positioning system (GPS) time source comprising:
- an oscillator adapted to provide an uncompensated frequency signal having a quantity of frequency error over a time period relative to a desired frequency such that the uncompensated frequency signal has an average uncompensated frequency which is different than the desired frequency;
frequency conversion circuitry receiving the uncompensated frequency signal and a control signal as inputs, wherein during operation as a time source the frequency conversion circuitry provides as an output a compensated frequency signal as a function of the uncompensated frequency signal and the control signal, the compensated frequency signal having an average compensated frequency which is closer to the desired frequency than is the average uncompensated frequency;
a temperature sensor sensing a temperature of the oscillator and providing an output indicative of the sensed temperature;
frequency error determining circuitry coupled to the temperature sensor and generating the control signal as a function of the sensed temperature, and thereby as a function of a quantity of frequency error in the uncompensated frequency signal; and
a counter receiving the compensated frequency signal from the frequency conversion circuitry as an input, the counter providing as an output a digital representation of a time period based upon the compensated frequency signal.
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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.
75 Citations
17 Claims
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1. A global positioning system (GPS) time source comprising:
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an oscillator adapted to provide an uncompensated frequency signal having a quantity of frequency error over a time period relative to a desired frequency such that the uncompensated frequency signal has an average uncompensated frequency which is different than the desired frequency; frequency conversion circuitry receiving the uncompensated frequency signal and a control signal as inputs, wherein during operation as a time source the frequency conversion circuitry provides as an output a compensated frequency signal as a function of the uncompensated frequency signal and the control signal, the compensated frequency signal having an average compensated frequency which is closer to the desired frequency than is the average uncompensated frequency; a temperature sensor sensing a temperature of the oscillator and providing an output indicative of the sensed temperature; frequency error determining circuitry coupled to the temperature sensor and generating the control signal as a function of the sensed temperature, and thereby as a function of a quantity of frequency error in the uncompensated frequency signal; and a counter receiving the compensated frequency signal from the frequency conversion circuitry as an input, the counter providing as an output a digital representation of a time period based upon the compensated frequency signal. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9)
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10. A global positioning system (GPS) receiver comprising:
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GPS signal receiving means for receiving Y-code modulated GPS signals from a plurality of GPS satellites; signal processing means for directly acquiring from the modulated GPS signals the Y-code used to modulate the GPS signals; low power time source means for providing to the signal processing means a digital representation of a time period for use in direct Y-code acquisition, the low power time source means comprising; an oscillator adapted to provide an uncompensated frequency signal having a quantity of frequency error over a time period relative to a desired frequency such that the uncompensated frequency signal has an average uncompensated frequency which is different than the desired frequency; and a counter operably coupled to the oscillator and generating as a function of the uncompensated frequency signal a digital representation of a time period; and compensation means for compensating the digital representation of the time period in order to minimize temperature dependent errors in the digital representation of the time period. - View Dependent Claims (11, 12, 13, 14, 15, 16)
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17. A method of providing a high accuracy time source for use in a global positioning system receiver for direct Y-code acquisition of GPS satellite signals, the method comprising:
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providing an uncompensated clock signal having a quantity of frequency error over a time period relative to a desired frequency such that the uncompensated clock signal has an average uncompensated frequency which is different than the desired frequency; sensing a temperature affecting the frequency error in the uncompensated clock signal; generating a control signal as a function of the sensed temperature, and thereby as a function of the quantity of frequency error over the time period; XORing the uncompensated clock signal and the control signal to provide a compensated clock signal; and counting cycles of the compensated clock signal to provide a digital representation of the time period.
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Specification