Low-Power System Clock Calibration With Periodic Reference Timing
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Solution Overview
Problem
Implantable medical devices, particularly those with small form factors like leadless pacemakers, face challenges in achieving high clocking accuracy while minimizing current drain due to the use of low-power oscillators, which suffer from inaccuracies related to long-term stability, temperature characteristics, and trim resolution.
Innovation Solution
A calibration routine is periodically performed using a high accuracy reference clock to adjust the low-power system clock, incorporating a delta-sigma loop to integrate and compensate for clock errors over time, allowing the system clock to maintain accuracy while reducing current consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If a low-power oscillator is used for the system clock, then current drain is reduced, but clocking accuracy deteriorates due to poor long-term stability, temperature characteristics, and trim resolution
Solution Approach 1:
The patent employs periodic action by switching between two clock sources: a low-power oscillator for normal operation and a high-accuracy reference clock for periodic calibration. The reference clock is activated only during calibration routines to correct drift and accuracy degradation, allowing the system to maintain high accuracy without continuously consuming high power. This periodic alternation resolves the contradiction by providing high accuracy only when needed rather than continuously.
Solution Approach 2:
The patent implements feedback through a calibration routine that periodically measures the deviation of the low-power system clock from the high-accuracy reference clock and adjusts the system clock accordingly. This feedback mechanism corrects accumulated errors in the low-power oscillator's timing, maintaining accuracy over extended periods without requiring continuous high-power operation.
2Measurement precision
If a high accuracy reference clock is used continuously, then clocking accuracy is maintained, but current drain increases substantially
Solution Approach 1:
Instead of continuously operating the high-accuracy reference clock, the system uses it periodically only during calibration routines. The reference clock is activated, performs accuracy measurement and correction, then is deactivated while the low-power oscillator continues normal operation. This periodic usage pattern maintains accuracy benefits while dramatically reducing average power consumption.
Solution Approach 2:
The patent extracts the high-accuracy timing function from continuous operation and applies it selectively only during calibration events. The high-accuracy reference clock is taken out of the continuous operational loop and used only when correction is needed, separating the functions of continuous low-power timing and periodic high-accuracy calibration.
3Volume of moving object
If the housing form factor is made extremely small for leadless implantation, then device miniaturization is achieved, but battery capacity is limited which constrains operational duration
Solution Approach 1:
The patent applies periodic action to power management by using a low-power oscillator for continuous operation and activating high-power components (reference clock, telemetry modules, processing functions) only during periodic calibration and communication events. This duty-cycled operation pattern extends the effective operational duration by minimizing average power consumption while maintaining small form factor constraints.
Solution Approach 2:
The system dynamically adjusts its power consumption profile by transitioning between low-power and high-power states based on operational needs. The clocking system dynamically switches between reference and low-power oscillators, and other subsystems dynamically activate only when required, creating a dynamic power management strategy that maximizes operational duration within small form factor constraints.
Data Source
AI summary
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.