Communication device with a self-calibrating sleep timer

• US 6,473,607 B1
• Filed: 04/30/1999
• Issued: 10/29/2002
• Est. Priority Date: 06/01/1998
• Status: Active Grant

• Current Assignee: Avago Technologies International Sales Pte Limited (Broadcom, Inc.)
• Original Assignee: Broadcom Corporation (Broadcom, Inc.)
• Inventors: Shohara, Aki, Lei, Emilia Vailun
• Primary Examiner(s): Nguyen, Lee
• Application Number:
  US09/302,447
• Time in Patent Office: 1,278 Days
• Field of Search: 455/343, 455/255, 455/257, 455/258, 455/259, 455/574, 340/7.32, 340/7.38, 370/311, 375/354
• US Class Current: 455/343.1
• CPC Class Codes: H04W 52/0216 using a pre-established activity schedule, e.g. traffic indication frame
• CPC Class Codes: H04W 52/0229 where the received signal is a wanted signal
• CPC Class Codes: H04W 52/0293 having a sub-controller with a low clock frequency switching on and off a main controller with a high clock frequency
• CPC Class Codes: H04W 56/0035 detecting errors in frequency or phase
• CPC Class Codes: Y02D 30/70 in wireless communication networks

Abstract

The present invention provides for a system for operating a communication device (20) for reception of scheduled intermittent information messages (22) with a dual mode timer (70) that extends battery life. A controller (50) schedules the timer (70) to power down all idle components of the device (20) between message receptions in a power saving sleep mode to conserve battery power. During active mode when the device is fully active in reception of messages, the timer (70) uses a reference oscillator (90) with a relatively high frequency to support digital processing by the receiver (26). During sleep mode when only the timer is powered on, a much lower frequency sleep oscillator (96) is used to maintain the lowest possible level of power consumption within the timer itself. The timer (70) has provision for automatic temperature calibration to compensate for timing inaccuracies inherent to the low-power low-frequency crystal oscillator (96) used for the sleep mode. The resultant improvement in timer accuracy during sleep mode eliminates the need for an initial reacquisition period following wake up in active mode, thereby reducing battery drain in active mode as well.

Claims

1. A system for operating a battery operated communication device with reduced power consumption wherein the communication device is adapted to receive radio signals containing intermittently scheduled digital messages, the communication device comprising

receiver means for frequency down conversion of the radio signals and demodulation of the digital messages;

a dual mode timer for continually maintaining system time while operating in one of two modes, the modes comprising an active mode and a sleep mode;

controller data processing means for data processing of the demodulated message data to extract the messages;

a reference oscillator for generating a reference clock, wherein the frequency of said reference clock is high enough to serve as clocking requirements for digital processing in the receiver and controller during the active mode, and wherein the frequency of the reference clock is responsive to input of an automatic frequency control word to the reference oscillator;

a sleep oscillator for generating a frequency which is low relative to the frequency of the reference clock and wherein power consumption of the sleep oscillator is very low relative to the power consumption of the reference oscillator; and

controller means for supervising operation of the communication device, wherein the supervision is executed by a microprocessor operation with program memory contained in a storage register,

wherein the timer for continually maintaining system time while operating in one of two modes, comprises a reference counter for modulus counter means that counts cycles of the reference clock up to a modulus value stored in a reference counter modulus register and resetting to zero at the next clock count, the reference counter generating system time during active mode in units of reference clock number represented by the current value in the reference counter, the reference counter generating a frame epoch output at the time of the reset, the reference counter also generating shifts in system time in units of reference clock cycles when a modulus value other than nominal is written to the reference counter modulus register.

2. The system of claim 1 wherein said timer further includes a sleep counter for accumulator means that successively sums a fractional number, or sleep counter increment stored in a sleep increment register by a controller calibration algorithm, wherein the sleep increment is equal to the number of frames per sleep oscillator cycle, the accumulator means successively adding the sleep increment register value but retaining only the fractional part of accumulation and generating an integer carry epoch each time an integer carry occurs in the accumulation, the sleep counter clocked by the sleep clock so that accumulation occurs at the rate the sleep clock frequency, said integer carry epochs generated by the sleep counter therefore representing frame boundary epochs.

3. The system of claim 1 wherein said timer further includes a frame counter that provides for modulus counter means that counts input frame epochs generated by either the reference counter or the sleep counter, the selection thereof dictated by a mode switch, said mode switch having two switch states, one state representing the active mode when the frame epoch source is the reference counter and the other switch state representing the sleep mode when the frame epoch source is the sleep oscillator, the mode switch being responsive to mode control logic, the frame counter maintaining continuity of count through changes in mode switch state, the frame counter counting up to the modulus value contained in a frame counter modulus register and resetting back to zero at the next clock cycle, the frame counter generating a multiframe epoch at each frame counter reset, the frame counter thereby generating system time in units of frame number in either active mode or sleep mode as represented by the current frame counter value.

4. The system of claim 1 wherein said frame counter provides modulus counter means to count up to the modulus value stored in a frame modulus register and resets back to zero on the next count.

5. The system of claim 1 wherein system time is defined in active mode as the triple (reference clock number, frame number, multiframe number) corresponding respectively to current count of the three registers (reference counter, frame counter, multiframe counter), and similarly defined in sleep mode except that reference clock number is undefined and ignored during sleep mode, system time being continuously generated as the mode switch alternates its state between active and sleep mode.

6. A system for operating a battery operated communication device with reduced power consumption wherein the communication device is adapted to receive radio signals containing intermittently scheduled digital messages, the communication device comprising:

receiver means for frequency down conversion of the radio signals and demodulation of the digital messages;

a dual mode timer that continually maintains system time while operating in one of two modes, the modes comprising an active mode and a sleep mode;

controller data processing means for data processing of the demodulated message data to extract the messages;

a reference oscillator that generates a reference clock, wherein the frequency of the reference clock is high enough to serve as clocking requirements for digital processing in the receiver means and the controller data processing means during the active mode, and wherein the frequency of the reference clock is responsive to input of an automatic frequency control word to the reference oscillator;

a sleep oscillator that generates a frequency which is low relative to the frequency of the reference clock and wherein power consumption of the sleep oscillator is very low relative to the power consumption of the reference oscillator; and

controller means for supervising operation of the communication device, wherein the supervision is executed by a microprocessor operation with program memory contained in a storage register,

wherein the controller data processing means performs a sleep mode fine adjustment to the timer to reduce timing error accumulated during the sleep mode to about a reference oscillator clock cycle whereby synchronization for digital processing by the receiver means is maintained, and

wherein said controller means includes a controller scheduling means for scheduling commands for supervision of the communication device, an event scheduler means for receiving scheduling commands, and a controller frequency tracking means for providing for automatic frequency control, wherein received downconverted signals are processed to generate the frequency control word for the reference oscillator at the rate of once per message reception such that the frequency of the reference clock is frequency-locked to the received signal, and

wherein said controller scheduling means is adapted to write command records to the event scheduler means, said records effecting power savings in the communication device by scheduling events that realize power savings, the event scheduler means being contained in program memory in the storage register, the write command records including;

a first command to cause execution of a controller timer calibration algorithm, scheduled for shortly after turn on of the communication device, said first command to provide for calculation of a correct value of a sleep counter increment to compensate for sleep oscillator error, thereby enabling synchronous operation of the communication device,

a second command to execute a controller sleep mode adjustment algorithm, scheduled for immediately following termination of the sleep mode and start of the active mode and prior to a first frame epoch in the active mode, thereby limiting accumulation of system time error during the sleep mode to less than one reference oscillator cycle, and thereby enabling synchronous operation of the communication device,

a third command to cause the controller means to execute a time track algorithm to update time tracking, scheduled for the end of each active mode interval, thereby avoiding possible accumulation of system time error due to repetitive occurrences of the sleep mode, and thereby enabling synchronous operation of the communication device,

downconversion commands to the receiver means to perform downconversion and synchronous demodulation and the controller means to process received messages, with event times coinciding with message arrival times, with no requirement to schedule reception and controller processing for reacquisition owing to synchronous operation of the communication device, thereby minimizing power consumption for signal processing during the active mode,

power controller commands to a power controller to selectively power up components of the communication device only when needed, where event times are precisely designated so that power up intervals are the minimum interval required, as enabled by synchronous operation of the communication device, thereby avoiding power waste on timing margins that compensate for system time uncertainties, and

mode commands to a mode controller to change the state of the mode switch into and out of the active mode with corresponding event times specified such that the sleep mode duty cycle with low power consumption is maximized and the active mode duty cycle with relatively high power consumption is minimized, as made possible by the synchronous operation of the communication device.

7. A system for operating a battery operated communication device with reduced power consumption wherein the communication device is adapted to receive radio signals containing intermittently scheduled digital messages, the communication device comprising:

receiver means for frequency down conversion of the radio signals and demodulation of the digital messages;

a dual mode timer for continually maintaining system time while operating in one of two modes, the modes comprising an active mode and a sleep mode;

controller data processing means for data processing of the demodulated message data to extract the messages;

a reference oscillator for generating a reference clock, wherein the frequency of the reference clock is high enough to serve as clocking requirements for digital processing in the receiver and controller during the active mode, and wherein the frequency of the reference clock is responsive to input of an automatic frequency control word to the reference oscillator;

a sleep oscillator for generating a frequency which is low relative to the frequency of the reference clock and wherein power consumption of the sleep oscillator is very low relative to the power consumption of the reference oscillator;

controller means for supervising operation of the communication device, wherein the supervision is executed by a microprocessor operation with program memory contained in a storage register, the controller means including controller scheduling means for scheduling commands for supervision of the communication device, event scheduler means for receiving scheduling commands, and controller frequency tracking means for providing for automatic frequency control wherein received down converted signals are processed to generate a frequency control word for the reference oscillator at the rate of once per message reception such that the frequency of the reference oscillator clock is frequency-locked to the received signal; and

means for automatic calibration of the timer in an environment of changing temperature, including;

temperature sensing means for obtaining temperature measurements of the low-frequency oscillator;

a sleep increment register for storing sleep increment values, and storage means containing a microprocessor program and data memory and register data memory, and

a calibration table maintained in volatile memory in the storage means such that the calibration table is initially empty at power up of the communication device, the calibration table thereafter holding calibration records, each record comprised of a sleep increment value calculated from sleep oscillator calibration data and temperature of the sleep oscillator during said calibration,

wherein initially after power up of the communication device, the controller schedules a timer calibration algorithm and temperature measurement at time of calibration to generate a first record for the calibration table and an initial value for the sleep increment in the sleep increment register, and

thereafter temperature measurement is performed periodically at a pre-specified period, and if temperature remains constant, no re-calibration is required and no action is taken, but if temperature changes, the new temperature is maintained in a record in the calibration table and the corresponding calibration value for sleep increment is loaded into the sleep increment register, thereby re-calibrating the sleep timer for the new temperature.

8. The system of claim 7 wherein if temperature changes and the new temperature is not in a record in the calibration table, the controller schedules the calibration algorithm to obtain a new calibration value, the pair of new temperature and new calibration values being entered as a new record in the calibration table, and the new calibration value is written to the sleep increment register, thereby re-calibrating the sleep timer for the new temperature.

9. The system of claim 8 wherein the automatic calibration of timer for temperature change continually maintains the correct value of sleep increment in the timer, thereby preserving accurate system time and synchronous operation of the communication device, thereby preserving power savings in an environment of changing temperature.

10. A system for operation of a communication device adapted to be operated by a battery for reception of scheduled intermittent information messages comprising:

a receiver for receiving the messages,

a dual mode timer, for continually maintaining time and operable in two modes, an active mode and a power saving sleep mode,

a controller for scheduling the timer to power down idle Components of the receiver between message receptions in the Power saving sleep mode to conserve battery power,

a reference oscillator for controlling the timer operative during the active mode when the device is fully active in reception of messages, said reference oscillator operating with a relatively high frequency to support digital processing by the receiver,

a sleep oscillator operative during the sleep mode when only the timer is powered ON, the sleep oscillator operative at a much lower frequency than the reference oscillator for maintaining the lowest possible level of power consumption within the timer,

means for automatic temperature calibration of the timer to compensate for timing inaccuracies inherent to the sleep oscillator used for the sleep mode,

means for automatic calibration of the timer in an environment of changing temperature, including a real-time clock powered with a backup battery that operates continually through power down of the communication device,

temperature sensing means for obtaining temperature measurement of the low-frequency oscillator, and

controller means for supervising operation of the communication device, wherein supervision is executed by a microprocessor operation with program memory contained in a storage register, the storage register having a non-volatile memory, and a calibration table maintained in the non-volatile memory such that at power up of the communication device, contents of the calibration table present just prior to power down of the communication device remain intact at power up of the communication device, the calibration table holding calibration records, each record comprised of a sleep increment value obtained by a controller sleep oscillator calibration algorithm and a temperature measurement of the sleep oscillator at the time of oscillator calibration.

11. The system of claim 10, further including means for automatic calibration of the timer

wherein initially after first power up of the communication device, a time stamp is affixed to the calibration table, said time stamp indicating an expiration time that is a pre-specified interval of time into the future, where said prespecified interval is an aging allowance for the table, the controller schedules the timer calibration algorithm, and schedules temperature measurement at time of said calibration, to generate the first record for the calibration table and an initial value for the sleep increment in the sleep increment register,

thereafter temperature measurement is performed periodically at a pre-specified period,

wherein if temperature remains constant no re-calibration is required and no action is taken,

if temperature changes and the new temperature is in a record in the calibration table the corresponding calibration value in said record is loaded into the sleep increment register, thereby re-calibrating the sleep timer for the new temperature, and

if temperature changes and the new temperature is not in a record in the calibration table, the controller schedules the sleep oscillator calibration algorithm to obtain a new calibration value, and schedules a new temperature measurement, the pair of new temperature and new calibration value entered as a new record in the calibration table, and the new calibration value written to the sleep increment register, thereby re-calibrating the sleep timer for the new temperature.

12. The system of claim 11 wherein at subsequent power up of the communication device

if said time stamp of the calibration table has expired, the calibration table is purged and new time stamp affixed with new expiration time, and said calibration method resumes as in initial power up of the communication device, thereby ensuring that invalidation of calibration data in the calibration table due to aging of the sleep oscillator crystal does not occur,

if said time stamp of the calibration table has not expired the calibration method resumes as in initial power-up of the calibration method but now generally starting with a non-empty calibration table.

13. The system of claim 12 wherein the automatic calibration of timer for temperature change continually maintains the correct value of sleep increment in the timer, thereby preserving accurate system time and synchronous operation of the communication device and preserving power savings in an environment of changing temperature.