SiRF’s Low Power Receiver Advances

Jerry Knight, Greg Turetzky, Charles Norman and Dennis Hilgenberg

Abstract:	The SiRFstar/LXm” chipset offers low cost, high capa-bility GPS performance in a very small form factor. It features a low power Real Time Clock (RTC), built-in power control, 12 parallel tracking channels, 240 parallel acquisition taps and 3.3 V operation. Three operating modes have been developed to provide the high perform-ance of SiRFstarTM receivers to low power applications. These are TricklePowerTM, SnapStartw and Push-to-FixTM. The center of the LX power management system is the RTC and power control. Software can command the LX to go to sleep and wake up any time within 254 days at a resolution of< 4 ms. The RTC will restart the receiver at the prescribed time and reset GPS time to a precision of 1 ps. The LX can independently power down its RF, signal processing and microprocessor sections. In sleep configu-ration power consumption is reduced to less than 1.0 mA. The RTC is driven by a low cost off-the-shelf 32768 Hz oscillator. Special software algorithms calibrate this os-cillator to an accuracy of a few PPM with only a minimal calibration time, The oscillator, RTC and critical static RAM together consume less than 10 pA if the rest of the receiver is powered off. In TricklePower mode the SiRFstar receiver turns itself on and off at a prescribed duty cycle but continues to make high quality GPS measurements as if it were run-ning continuously. A fill set of high quality GPS pseu-dorange and delta-range measurements are made within 200 ms of turning on. The receiver then shuts itself off until time for the next measurement. This represents a nearly 800/0 saving in power for once per second meas-urements and a 96% savings for once per 5 second meas-urements. Experiments have shown that this mode of op-eration can be extended to once per 15 minute measure-ments without loss of performance. SnapStart allows the SiRFstar receiver to start nearly in-stantly after short periods when the receiver is turned off. An example application is restarting an automobile after a short stop at the comer store. GPS time is recovered from the RTC and previous navigation and satellite position data is stored in non-volatile SRAM. With this informa-tion available, the receiver is able to initialize itself and the microprocessor and make its first position fix in less than 1.5 seconds. If existing satellite position data is not fresh, another 1.5 seconds are required to freshen the data. Push-to-Fix combines features of TricklePower and SnapStart. Here the LX puts itself to sleep, but it is awak-ened by an external signal. The receiver then starts itself, resets GPS time from the RTC and uses saved satellite and navigation data to begin making measurements after only 200 ms. The receiver can then either automatically go back to sleep or continue running for a prescribed pe-riod.
Published in:	Proceedings of the 11th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1998) September 15 - 18, 1998 Nashville, TN
Pages:	299 - 305
Cite this article:	Knight, Jerry, Turetzky, Greg, Norman, Charles, Hilgenberg, Dennis, "SiRF’s Low Power Receiver Advances," Proceedings of the 11th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1998), Nashville, TN, September 1998, pp. 299-305.
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