Method and apparatus for real time clock (RTC) brownout detection
First Claim
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1. A method of determining if a real time clock (“
- RTC”
) in a global positioning system (“
UPS”
) receiver system is accurate enough to be used on start up of the GPS receiver, the method comprising;
transferring the time kept by the RTC clock to a GPS clock of the GPS receiver system;
estimating the position of visible satellites, wherein the GPS clock is updated with signals from the RTC clock;
based on the estimated position of the visible satellites, measuring a pseudo-noise (“
PN”
) code for each of the visible satellites;
calculating an expected current full PN code phase for each of the visible satellites;
computing the location of the GPS receiver using the expected current full PN code phases;
comparing the computed location of the GPS receiver to a previously-computed location of the GPS receiver in units of time;
determining whether the computed location of the GPS receiver has changed more than a predetermined threshold amount from the previously-computed location; and
responsive to the determined amount exceeding the predetermined threshold amount, establishing a new GPS clock by acquiring the visible satellites using conventional methods.
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Abstract
A method and apparatus for real time clock brownout detection. A low power real time clock (RTC) operates continuously to keep time in a global positioning system (GPS) receiver while some receiver components are powered down. In various embodiments, a brownout detector circuit detects a loss of RTC clock cycles. If a loss of RTC clock cycles exceeds a predetermined threshold such that the RTC is not reliable for GPS navigation, an RTC status signal so indicates.
14 Citations
20 Claims
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1. A method of determining if a real time clock (“
- RTC”
) in a global positioning system (“
UPS”
) receiver system is accurate enough to be used on start up of the GPS receiver, the method comprising;transferring the time kept by the RTC clock to a GPS clock of the GPS receiver system; estimating the position of visible satellites, wherein the GPS clock is updated with signals from the RTC clock; based on the estimated position of the visible satellites, measuring a pseudo-noise (“
PN”
) code for each of the visible satellites;calculating an expected current full PN code phase for each of the visible satellites; computing the location of the GPS receiver using the expected current full PN code phases; comparing the computed location of the GPS receiver to a previously-computed location of the GPS receiver in units of time; determining whether the computed location of the GPS receiver has changed more than a predetermined threshold amount from the previously-computed location; and responsive to the determined amount exceeding the predetermined threshold amount, establishing a new GPS clock by acquiring the visible satellites using conventional methods. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9)
- RTC”
-
10. A method of updating a real time clock (“
- RTC”
) in a global positioning system (“
GPS”
) receiver system that uses significantly less power than a GPS clock of the GPS receiver system, the method comprising;receiving a wake up command at a GPS receiver of the GPS receiver system while the GPS receiver is in a powered down mode; powering up selected components of the GPS receiver in response to receiving the wake up command; measuring an operating temperature of the RTC of the GPS receiver; calculating a frequency error associated with the RTC based upon the measured operating temperature of the RTC; updating the RTC with the frequency error; determining a status of the updated RTC, wherein the status is one of GOOD and NOT GOOD; responsive to determining that the status of the updated RTC is GOOD;
configuring the updated RTC to keep time of the GPS receiver system instead of the GPS clock;
, andpowering down the selected components of the GPS receiver. - View Dependent Claims (11, 12, 13, 14, 15)
- RTC”
-
16. A method of updating a real time clock (“
- RTC”
) in a global positioning system (“
GPS”
) receiver system that uses significantly less power than a GPS clock of the GPS receiver system, the method comprising;receiving a wake up command at a GPS receiver of the GPS receiver system while the GPS receiver is in a powered down mode; powering up selected components of the GPS receiver in response to receiving the wake up command; measuring an operating temperature of the RTC of the GPS receiver; calculating a frequency error associated with the RTC based upon the measured operating temperature of the RTC; updating the RTC with the frequency error powering down the selected components of the GPS receiver, wherein the wake up command is initiated by a user of the GPS receiver corresponding to a positional query of the GPS receiver; providing a clocking signal from the RTC to an edge aligned ration counter (“
EARC”
);aligning the clocking signal from the RTC with a clock signal from a GPS clock using the EARC; and transferring the time kept by the RTC clock to the GPS clock. - View Dependent Claims (17, 18, 19)
- RTC”
-
20. A method of updating a real time clock (“
- RTC”
) in a global positioning system (“
GPS”
) receiver system that uses significantly less power than a GPS clock of the GPS receiver system, the method comprising;receiving a wake up command at a GPS receiver of the GPS receiver system while the GPS receiver is in a powered down mode; powering up selected components of the GPS receiver in response to receiving the wake up command; measuring an operating temperature of the RTC of the GPS receiver;
wherein the step of measuring the operating temperature of the RTC includes;measuring a current operating temperature of the RTC; retrieving an operating temperature of the RTC taken at the time of an earlier wake up command from the temperature/frequency error table; averaging the current operating temperature and the operating temperature taken at the earlier time; and calculating the frequency error associated with the RTC based upon the average operating temperature of the RTC calculating a frequency error associated with the RTC based upon the measured operating temperature of the RTC; updating the RTC with the frequency error; and powering down the selected components of the GPS receiver.
- RTC”
Specification