Method and Apparatus for Real Time Clock (RTC) Brownout Detection

• US 20090322606A1
• Filed: 06/22/2009
• Published: 12/31/2009
• Est. Priority Date: 10/30/2001
• Status: Active Grant

• Current Assignee: CSR Technology Incorporated (Qualcomm, Inc.)
• Original Assignee: SIRF Technology Incorporated (Qualcomm, Inc.)
• Inventors: Gronemeyer, Steven A.
• Granted Patent: US 7,865,307 B2
• Time in Patent Office: Days
• US Class Current: 342/357.62
• CPC Class Codes: G01R 19/16542 for batteries charge condition monitoring in G01R31/36
• CPC Class Codes: G01S 19/23 Testing, monitoring, correcting or calibrating of receiver elements
• CPC Class Codes: G01S 19/235 Calibration of receiver components
• CPC Class Codes: G01S 19/34 Power consumption
• CPC Class Codes: G04C 10/04 with means for indicating the condition of the power supply in general G01R31/36
• CPC Class Codes: G04F 5/00 Apparatus for producing preselected time intervals for use as timing standards generating clock signals for electric digital computers G06F1/04
• CPC Class Codes: G04G 19/12 Arrangements for reducing power consumption during storage
• CPC Class Codes: G06F 1/14 Time supervision arrangements, e.g. real time clock
• CPC Class Codes: G06F 1/30 Means for acting in the event of power-supply failure or interruption, e.g. power-supply fluctuations for resetting only G06F1/24
• CPC Class Codes: G06F 1/3203 Power management, i.e. event-based initiation of a power-saving mode
• CPC Class Codes: G06F 1/3287 by switching off individual functional units in the computer system
• CPC Class Codes: Y02D 10/00 Energy efficient computing, e.g. low power processors, power management or thermal management

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.

Claims

1-28. -28. (canceled)

29. A method of determining of a real time clock (“

RTC”

) in a global positioning system (“

GPS”

) 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 exceeding the predetermined threshold amount, establishing a new GPS clock by acquiring the visible satellites using conventional methods.

30. The method of claim 29, wherein the step of transferring the time kept by the RTC clock to the GPS clock includes the steps of:

providing a clocking signal from the RTC to an edge aligned ratio counter (“

EARC”

); and

;

aligning the clocking signal from the RTC with a clock signal from a GPS clock using the EARC.

31. The method of claim 29, where the predetermined threshold amount is ±

0.5 ms.

32. The method of claim 29, where the RTC includes a K32 oscillator (with a nominal 32,768 Hz) that generates a K32 clock signal.

33. The method of claim 32, further including the steps of:

measuring an operating temperature of the K32 oscillator of the RTC;

calculating a frequency error associated with the K32 oscillator based upon the measured operating temperature of the RTC; and

Updating the RTC with the frequency error.

34. The method of claim 33, further including steps of:

Measuring an operating temperature of the GPS clock;

Calculating a frequency error associated with the GPS clock based upon the measured operating temperature of the GPS clock; and

Updating the GPS clock with the frequency error.

35. The method of claim 29, further including the step of responsive to the determined amount not exceeding the predetermined threshold amount, updating the RTC clock with the updated GPS clock.

36. The method of claim 35, wherein the step of updating the RTC clock with the updated GPS clock includes the steps of:

Providing a clocking signal from the updated GPS clock to the EARC; and

aligning the clocking signal from the updated GPS clock with a clock signal from the RTC clock using the EARC.

37. 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 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; and

powering down the selected components of the GPS receiver.

38. The method of claim 37, wherein the wake up command is a predetermined wake up command provided on a periodic basis.

39. The method of claim 37, wherein the wake up command is initiated by a user of the GPS receiver corresponding to a positional query of the GPS receiver.

40. The method of claim 39, further including the steps of:

providing a clocking signal from the RTC to an edge aligned ratio 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.

41. The method of claim 40, further including the steps of:

Determining whether the RTC clock is losing cycles, wherein the loss of cycles is above a predetermined threshold; and

Responsive to the loss of cycles being below the predetermined threshold, using the GPS clock to acquire satellites.

42. The method of claim 41, wherein the determination of whether the RTC clock is losing cycles is made by a brownout detection circuit coupled to the RTC.

43. The method of claim 42, wherein the brownout detection circuit comprises:

a detection circuit that receives the RTC clock signal and determines whether the RTC clock is losing cycles, wherein the detection circuit is calibrated to determine whether a loss of cycles is above the predetermined threshold; and

a status circuit that stores a signal output by the detection circuit and outputs a status signal indicating the RTC clock is one of GOOD and NOT GOOD.

44. The method of claim 37, further including the step of storing the operating temperature and the frequency error of the RTC in a temperature/frequency error table in a memory of the GPS receiver.

45. The method of claim 37, 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.

46. The method of claim 37, further including the steps of:

Measuring an operating temperature of a GPS clock of the GPS receiver;

calculating a frequency error associated with the GPS clock based upon the measured operating temperature of the GPS clock;

Updating the GPS clock with the frequency error.

47. The method of claim 46, further including the step of storing the operating temperature and the frequency error of the GPS clock in the temperature/frequency error table.