Implantable Medical Device Clock Calibration
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Solution Overview
Problem
Implantable medical devices (IMDs) face challenges with size constraints and power consumption due to the need for both low frequency and high frequency timing sources, particularly for RF communication and therapy/sensing functions, where traditional crystal oscillators are large, expensive, and power-intensive.
Innovation Solution
A method involving a low frequency clock and a high frequency clock, where the high frequency clock is used to calibrate the low frequency clock, reducing power consumption by selectively enabling the high frequency clock and continuously enabling the low frequency clock, using a non-crystal oscillator for therapy/sensing and a crystal oscillator for RF communication.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a high frequency crystal oscillator is used for RF communication, then stable frequency is achieved, but power consumption increases significantly
Solution Approach 1:
The patent divides the timing source into two separate crystal oscillators: a high frequency crystal oscillator dedicated to RF communication and a low frequency crystal oscillator for therapy and sensing timing. This segmentation allows each oscillator to operate independently at its optimal frequency, enabling the high frequency oscillator to be disabled during non-RF periods thereby reducing overall power consumption while maintaining frequency stability when RF communication is active
Solution Approach 2:
The patent implements dynamic control of the high frequency crystal oscillator by selectively enabling it only during RF communication activities and disabling it during non-RF periods. This dynamic power management approach maintains frequency stability when needed while minimizing power consumption during idle periods, directly resolving the contradiction between reliability and energy use
2Use of energy by moving object
If a low frequency crystal oscillator is used for therapy and sensing, then power consumption is reduced, but device size increases
Solution Approach 1:
The low frequency crystal oscillator serves multiple functions: it provides timing for therapy delivery, sensing operations, and acts as a reference for calibrating the high frequency oscillator. This multi-functionality allows the device to achieve low power consumption while maintaining compact size, as the single low frequency oscillator replaces what would otherwise require separate timing circuits
3Device complexity
If a single high frequency crystal oscillator is used for both RF communication and therapy timing, then device complexity is reduced, but power consumption increases continuously
Solution Approach 1:
The patent segments the timing functions into two separate crystal oscillators with distinct frequency ranges and dedicated purposes. The high frequency oscillator handles RF communication timing while the low frequency oscillator manages therapy and sensing timing, allowing independent power management and eliminating continuous power consumption of a single high frequency source
Solution Approach 2:
The patent implements a feedback mechanism where the low frequency crystal oscillator calibration system uses the high frequency oscillator's stability to calibrate its own frequency divider output. This feedback loop ensures accurate therapy timing while allowing the high frequency oscillator to be disabled during non-RF periods, reducing continuous power consumption
4Volume of moving object
If a low frequency non-crystal oscillator is used for therapy timing, then device size is reduced, but frequency stability deteriorates
Solution Approach 1:
The patent introduces the low frequency crystal oscillator as an intermediary between the high frequency crystal oscillator and the therapy timing system. The low frequency crystal provides stable frequency reference for therapy timing, while its output is further divided down to the required therapy rates, maintaining both compact size and frequency stability
Data Source
AI summary
Techniques for calibrating a low frequency (LF) clock of an IMD are disclosed, wherein the IMD also includes a high frequency (HF) clock. This includes determining an average, or a surrogate thereof, of how many HF clock cycles of a HF clock signal (produced by the HF clock) occur per LF clock cycle of a predetermined number N of LF clock cycles of the LF clock signal (produced by the LF clock), wherein N is an integer that is at least 2. This also includes comparing the average or a surrogate thereof to a corresponding target value that the average or the surrogate thereof would be equal to if the frequency of the LF clock signal equaled a target frequency for the LF clock, wherein the corresponding target value need not be an integer. The LF clock is calibrated by adjusting the frequency thereof based on results of the comparing.