Low-power system clock calibration based on a high-accuracy reference clock
First Claim
1. An implantable medical device (IMD) comprising:
- a processor;
a system clock that comprises a low power oscillator, according to which the processor operates the IMD;
a reference clock that comprises a high accuracy oscillator; and
a clock calibrator that periodically performs 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 clock calibrator comprises;
a controller that powers on the reference clock at a start of the calibration routine, and disables the reference clock at an end of the calibration routine;
a clock comparator that determines 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, wherein the clock comparator includes;
a system clock counter that is set equal to the fixed number of clock cycles and decrements by one for each clock cycle of the system clock, wherein the system clock counter stops when equal to zero; and
a reference clock counter that is set equal to the fixed number of clock cycles and decrements 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; and
a clock adjuster that adjusts a trim value of the system clock to compensate for the clock error.
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Accused Products
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.
8 Citations
14 Claims
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1. An implantable medical device (IMD) comprising:
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a processor; a system clock that comprises a low power oscillator, according to which the processor operates the IMD; a reference clock that comprises a high accuracy oscillator; and a clock calibrator that periodically performs 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 clock calibrator comprises; a controller that powers on the reference clock at a start of the calibration routine, and disables the reference clock at an end of the calibration routine; a clock comparator that determines 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, wherein the clock comparator includes; a system clock counter that is set equal to the fixed number of clock cycles and decrements by one for each clock cycle of the system clock, wherein the system clock counter stops when equal to zero; and
a reference clock counter that is set equal to the fixed number of clock cycles and decrements 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; anda clock adjuster that adjusts a trim value of the system clock to compensate for the clock error. - View Dependent Claims (2, 3, 4, 5, 6)
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7. An implantable medical device (IMD) comprising:
- An implantable medical device (IMD) comprising;
a processor; a system clock that comprises a low power oscillator, according to which the processor operates the IMD; a reference clock that comprises a high accuracy oscillator; and a clock calibrator that periodically performs 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.
- An implantable medical device (IMD) comprising;
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8. An implantable medical device (IMD) comprising:
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a system clock that comprises a low power oscillator; a reference clock that comprises a high accuracy oscillator; means for operating the IMD in accordance with the system clock; means for 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; means for powering on the reference clock at a start of the calibration routine; means for 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, wherein means for determining a clock error of the system clock further comprise; means for setting a system clock counter and a reference clock counter equal to the fixed number of clock cycles; means for decrementinq 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 means for decrementinq 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; and means for adjusting a trim value of the system clock to compensate for the clock error; and means for disabling the reference clock at an end of the calibration routine. - View Dependent Claims (9, 10, 11, 12, 13)
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14. An implantable medical device (IMD) comprising:
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a system clock that comprises a low power oscillator; a reference clock that comprises a high accuracy oscillator; means for operating the IMD in accordance with the system clock; and means for 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 system clock and the reference clock operate at a same clock frequency value.
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Specification