Method and apparatus for estimating local oscillator frequency for GPS receivers
First Claim
1. An apparatus for estimating frequency errors in a local oscillator signal used in GPS receivers, comprising:
- a local oscillator for generating the local oscillator signal and a sampling clock signal, wherein the sampling clock signal is derived from the local oscillator signal;
a sampling block coupled to the local oscillator, that receives an external reference signal with a known reference frequency and the sampling clock signal, and generates digital samples of the external reference signal; and
a local oscillator frequency error estimator module, that determines a frequency error in the local oscillator signal by comparing respective frequencies of the digital samples of the external reference signal and the sampling clock signal.
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Abstract
The present invention is a method and apparatus that produces an estimate of the local oscillator (LO) frequency error using an external reference signal. The error estimate can be used for LO calibration, correction and other purposes. The present invention does not require the external reference signal to be a precision reference signal, nor does the present invention require that the reference signal be continuously supplied. Further, the present invention can be implemented exclusively in software, and therefore does not add to the size or weight of any device that it is resident in. Thus, the present invention can be added to microcontrollers and various specialized programmable digital ICs that were not initially designed for this task.
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Citations
15 Claims
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1. An apparatus for estimating frequency errors in a local oscillator signal used in GPS receivers, comprising:
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a local oscillator for generating the local oscillator signal and a sampling clock signal, wherein the sampling clock signal is derived from the local oscillator signal; a sampling block coupled to the local oscillator, that receives an external reference signal with a known reference frequency and the sampling clock signal, and generates digital samples of the external reference signal; and a local oscillator frequency error estimator module, that determines a frequency error in the local oscillator signal by comparing respective frequencies of the digital samples of the external reference signal and the sampling clock signal. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8)
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9. A method of calibrating a local oscillator in a mobile GPS receiver, comprising:
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receiving an external reference signal with a known reference frequency from an external source providing the external reference signal; generating the a local oscillator signal; deriving a sampling clock signal from the local oscillator signal; sampling the external reference signal with the sampling clock signal, thereby generating digital samples of the external reference signal; and comparing respective frequencies of the digital samples of the external reference signal and the sampling clock signal, thereby estimating a frequency error in the local oscillator signal. - View Dependent Claims (10, 11, 12, 13, 14, 15)
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Specification