Communication device with a self-calibrating sleep timer

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.

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.

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.