Low-Power Oscillator Calibration for Accurate Timekeeping
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Solution Overview
Problem
Low-power oscillators in electronic devices exhibit wide tolerances and significant drift with temperature and voltage, leading to inaccuracies in time counting during low power mode operations.
Innovation Solution
A method is implemented to detect the removal of a power source, cease calibration of the low-power oscillator, determine correction factors based on calibration results, and adjust recalibration intervals to maintain accurate time counting, involving a stabilization period, periodic recalibrations, and retrospective corrections.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If the crystal-based oscillator is powered down in standby mode, then battery life is extended, but time counting accuracy deteriorates due to drift in the low-power oscillator
Solution Approach 1:
The patent implements periodic calibration where the low-power oscillator is calibrated against the crystal-based oscillator at regular intervals. The calibration results are stored and applied as correction factors during inter-calibration periods when the low-power oscillator operates independently, combining energy savings with maintained accuracy.
Solution Approach 2:
The system continuously monitors the drift of the low-power oscillator by periodically comparing it with the crystal-based oscillator reference. The calibration results provide feedback that is used to adjust and correct the low-power oscillator's timing, ensuring accuracy is maintained over time.
2Measurement precision
If calibration is performed frequently, then time counting accuracy is maintained, but energy consumption increases due to repeated activation of the crystal-based oscillator
Solution Approach 1:
The system performs calibration at predetermined regular intervals rather than continuously. The crystal-based oscillator is activated only during these periodic calibration events, while the low-power oscillator handles time counting during inter-calibration periods, optimizing the balance between accuracy and energy consumption.
Solution Approach 2:
The calibration interval can be dynamically adjusted based on the determined drift rate of the low-power oscillator. If drift is minimal, intervals can be extended; if drift increases, intervals are shortened, allowing the system to adapt to changing conditions while managing energy usage.
3Use of energy by moving object
If the low-power oscillator is used without calibration, then energy consumption is minimized, but time counting accuracy deteriorates significantly due to temperature and voltage drift
Solution Approach 1:
The system performs preliminary calibration of the low-power oscillator against the crystal-based oscillator before entering extended low-power operation. The calibration results and correction factors are stored in memory and applied during subsequent low-power operation, enabling accurate time counting without continuous high-power operation.
Solution Approach 2:
The calibration results and correction factors act as intermediaries that transfer timing accuracy from the crystal-based oscillator to the low-power oscillator. This allows the low-power oscillator to operate independently while maintaining accuracy through the applied correction factors.
Data Source
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AI summary
An electronic device has two oscillators, for example a first highly accurate crystal oscillator and a second less accurate low power oscillator. In a normal mode of operation, time is counted based on an output from the crystal oscillator, but in a low power mode of operation, time is counted based on an output from the less accurate oscillator. During the low power mode of operation, a calibration process is performed repeatedly. During a first calibration time period the second oscillator is calibrated against the first oscillator to obtain a first calibration result, and a recalibration is performed during a second calibration time period to obtain a second calibration result. A correction factor is determined from the first and second calibration results, and the correction factor is applied when subsequently counting time based on the output from the second oscillator.