Low-power system clock calibration based on a high-accuracy reference clock
First Claim
1. A method comprising:
- operating an implantable medical device (IMD) in accordance with a system clock that comprises a low power oscillator clock included in the IMD; and
periodically performing a calibration routine to calibrate the system clock based on the reference clock, wherein the system clock is continuously powered and the reference clock is powered during the calibration routine, wherein the reference clock comprises a crystal oscillator.
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Abstract
Various techniques are described for periodically performing a calibration routine to calibrate a low-power system clock within an implantable medical device (IMD) based on a high accuracy reference clock also included in the IMD. The system clock is powered continuously, and the reference clock is only powered on during the calibration routine. The techniques include determining a clock error of the system clock based on a difference between frequencies of the system clock and the reference clock over a fixed number of clock cycles, and adjusting a trim value of the system clock to compensate for the clock error. Calibrating the system clock with a delta-sigma loop, for example, reduces the clock error over time. This allows accurate adjustment of the system clock to compensate for errors due to trim resolution, circuit noise and temperature.
9 Citations
14 Claims
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1. A method comprising:
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operating an implantable medical device (IMD) in accordance with a system clock that comprises a low power oscillator clock included in the IMD; and periodically performing a calibration routine to calibrate the system clock based on the reference clock, wherein the system clock is continuously powered and the reference clock is powered during the calibration routine, wherein the reference clock comprises a crystal oscillator. - View Dependent Claims (4, 5, 6, 7)
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2. A method comprising:
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operating an implantable medical device (IMD) in accordance with a system clock that comprises a low power oscillator clock included in the IMD; and periodically performing a calibration routine to calibrate the system clock based on the reference clock, wherein the system clock is continuously powered and the reference clock is powered during the calibration routine, wherein periodically performing a calibration routine to calibrate the system clock further comprises; powering on the reference clock at a start of the calibration routine; determining a clock error of the system clock based on a difference between frequencies of the system clock and the reference clock over a fixed number of clock cycles of the system clock; adjusting a trim value of the system clock to compensate for the clock error; and disabling the reference clock at an end of the calibration routine, and wherein determining a clock error of the system clock further comprises; setting a system clock counter and a reference clock counter equal to the fixed number of clock cycles; decrementing the system clock counter by one for each clock cycle of the system clock, wherein the system clock counter stops when equal to zero; and decrementing the reference clock counter by one for each clock cycle of the reference clock, wherein the reference clock counter stops at a reference count value when the system clock counter is equal to zero, wherein the reference count value is indicative of the clock error of the system clock. - View Dependent Claims (3)
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8. A computer-readable storage medium comprising instructions that, when executed, cause a programmable processor to:
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operate an implantable medical device (IMD) in accordance with a system clock that comprises a low power oscillator clock included in the IMD; and periodically perform a calibration routine to calibrate the system clock based on the reference clock, wherein the system clock is continuously powered and the reference clock is powered during the calibration routine, wherein the system clock and the reference clock operate at a same clock frequency value. - View Dependent Claims (11, 12, 13, 14)
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9. A computer-readable storage medium comprising instructions that, when executed, cause a programmable processor to:
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operate an implantable medical device (IMD) in accordance with a system clock that comprises a low power oscillator clock included in the IMD; periodically perform a calibration routine to calibrate the system clock based on the reference clock, wherein the system clock is continuously powered and the reference clock is powered during the calibration routine; power on the reference clock at a start of the calibration routine; determine a clock error of the system clock based on a difference between frequencies of the system clock and the reference clock over a fixed number of clock cycles of the system clock; adjust a trim value of the system clock to compensate for the clock error; and disable the reference clock at an end of the calibration routine, wherein the instructions that cause the programmable processor to determine a clock error of the system clock further comprise instructions that cause the programmable processor to; set a system clock counter and a reference clock counter equal to the fixed number of clock cycles; decrement the system clock counter by one for each clock cycle of the system clock, wherein the system clock counter stops when equal to zero; and decrement the reference clock counter by one for each clock cycle of the reference clock, wherein the reference clock counter stops at a reference count value when the system clock counter is equal to zero, wherein the reference count value is indicative of the clock error of the system clock. - View Dependent Claims (10)
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Specification