Using telemetry downlink for real time clock calibration

• US 8,805,505 B1
• Filed: 01/25/2013
• Issued: 08/12/2014
• Est. Priority Date: 01/25/2013
• Status: Active Grant

• Current Assignee: Medtronic Incorporated (Medtronic Plc)
• Original Assignee: Medtronic Incorporated (Medtronic Plc)
• Inventors: Roberts, Melvin P.
• Primary Examiner(s): Wieland, Robert N
• Application Number:
  US13/749,852
• Publication Number:
  US 20140214109A1
• Time in Patent Office: 564 Days
• Field of Search: 607/27
• US Class Current: 607/27
• CPC Class Codes: A61N 1/025 Digital circuitry features of electrotherapy devices, e.g. memory, clocks, processors
• CPC Class Codes: A61N 1/37 Monitoring; Protecting
• CPC Class Codes: A61N 1/3706 Pacemaker parameters stimulation threshold A61N1/371
• CPC Class Codes: A61N 1/37252 Details of algorithms or data aspects of communication system, e.g. handshaking, transmitting specific data or segmenting data
• CPC Class Codes: G06F 1/12 Synchronisation of different clock signals provided by a plurality of clock generators

Abstract

An implantable medical device includes a local clock generator for generating a system clock signal. The local clock generator is periodically calibrated to maintain accuracy of the generated system clock signal. A clocking circuit is coupled to the local clock generator to provide the calibration factor for calibrating the local clock generator. The implantable medical device receives an accurate clock signal that is transmitted from an external device and the accurate clock signal is provided to the clocking circuit. The system clock signal is also provided to the clocking circuit and a computation is performed to derive the calibration factor.

Claims

1. An implantable medical device, comprising:

a first clock source configured to generate a first clock signal;

a second clock source configured to generate a second clock signal; and

a clocking circuit coupled to the first clock source and the second clock source, wherein the clocking circuit is configured to perform a calibration routine including comparing the first clock signal to the second clock signal, derive a weighing factor based on the relative magnitude of the first clock signal and the second clock signal, and generate a calibration factor based on the comparison and the weighting factor for calibrating the first clock source relative to the second clock source during a calibration routine.

2. The implantable medical device of claim 1, wherein the clocking circuit is configured to simultaneously compute a number of clock cycles of each of the first clock signal and the second clock signal during a first time interval and to generate the calibration factor based on the relative difference in the computed count of the clock cycles of the first clock signal and the second clock signal.

3. The implantable medical device of claim 2, wherein the clocking circuit is configured to determine a frequency of the second clock signal to determine whether the frequency is within a predetermined frequency range with respect to a frequency of the first clock signal.

4. The implantable medical device of claim 3, wherein the clocking circuit compares the computed number of clock cycles of the first clock signal to the second clock signal in response to the frequency being within the predetermined frequency range.

5. The implantable medical device of claim 3, wherein the clocking circuit compares the computed number of clock cycles of the first clock signal to a weighted count of the computed number of second clock signal cycles in response to the frequency falling outside of the predetermined frequency range.

6. The implantable medical device of claim 5, wherein the weighted count of the computed number of second clock signal cycles is computed based on the relative difference between the frequency of the second clock signal and the first clock signal.

7. The implantable medical device of claim 3, wherein the predetermined frequency has an upper limit and a lower limit based on a frequency of the local clock signal.

8. The implantable medical device of claim 3, wherein the upper limit and the lower limit are based on a target frequency range of the local clock signal.

9. The implantable medical device of claim 1, further comprising a calibration control circuit for generating a command signal to initiate the calibration routine.

10. The implantable medical device of claim 9, wherein the command signal is generated in response to expiration of a predetermined time interval.

11. The implantable medical device of claim 9, wherein the command signal is generated at a predefined time of day.

12. The implantable medical device of claim 1, wherein the clocking circuit is configured to compute a number of active edges of the first clock signal and the second clock signal during a fixed time interval and to generate the calibration factor based on the computed number of active edges.

13. The implantable medical device of claim 1, wherein the local clock generator is adjusted based on the calibration factor to generate an updated first clock signal.

14. The implantable medical device of claim 1, wherein the clocking circuit includes:

a first signal counter for receiving the first clock signal and counting the number of cycles of the first clock signal in a first duration;

a second phase detector for receiving the second clock signal and simultaneously counting the number of cycles of the second clock signal in a second duration; and

a phase comparator to generate the calibration factor based on a comparison of the number of cycles counted by the first signal counter during the given duration and the number of cycles counted by the second signal counter.

15. The implantable medical device of claim 14, wherein the first duration and the second duration are identical.

16. The implantable medical device of claim 14, wherein the first duration and the second duration are measured concurrently.