Low-Power Oscillator/Clock for Direct P-Code Acquisition

Raymond Filler and John Vig

Abstract:	Direct Pxode (re)aquisition requires a much higher accuracy clock than what is currently being used in GPS receivers. Until recently, clocks of sufficient accuracy could not be used in hand-held receivers because they required too much power. In this paper, the two low power clock technologies which are suitable for hand- held GPS receivers, the TCXO and the MCXO, are reviewed. It is shown that the microcomputer compensated crystal oscillator, MCXO, is an oscillator that is 100X more accurate than the next best low-power oscillator, the temperature compensated crystal oscillator, TCXO. The MCXO overcomes the limitations of the major type of precision low-power oscillator, TCXO. It employs external compensation, i.e., there is no crystal “pulling.” It thus permits the use of a low hysteresis, high-stability SC-cut crystal in a non-trimmed oscillator. Resonator self-temperature-sensing, using a dual mode oscillator, virtually eliminates all thermometry related errors. As a consequence, all basic TCXO limitations are overcome. MCXOs incorporating this technology are capable of providing at least 10 to lOO-times improvement in overall frquency accuracy when compared to conventional TCXOs. Timekeeping accuracy of 100~s for periods of an hour, with an input power of less than 40 milliwatts, is now available. Long term accuracy is parts in 10’ per year. The next best oscillator of similar accuracy is an oven controlled crystal oscillator, OCXO, which requires 1 W or more. Atomic clocks are more accurate than crystal oscillators, however, their high power requirements (and large size, weight and cost) make them unsuitable for small GPS receivers.
Published in:	Proceedings of the 51st Annual Meeting of The Institute of Navigation (1995) June 5 - 7, 1995 Antlers Doubletree Hotel Colorado Springs, CO
Pages:	405 - 411
Cite this article:	Filler, Raymond, Vig, John, "Low-Power Oscillator/Clock for Direct P-Code Acquisition," Proceedings of the 51st Annual Meeting of The Institute of Navigation (1995), Colorado Springs, CO, June 1995, pp. 405-411.
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