Oscillator Frequency Calibration Using External Sync Pulses
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Solution Overview
Problem
Integrated circuits lacking high-precision oscillators, such as those with less than 2% error, limit their use or require high-cost solutions, especially in systems without a CPU system.
Innovation Solution
A free-running oscillator is synchronized using external synchronisation pulses to achieve a target frequency without an internal reference clock, allowing it to operate independently once synchronized, with adjustments made through a frequency adjustment circuit using a counter and comparator to refine accuracy over time.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a free-running oscillator is used in integrated circuits, then cost is reduced and device complexity is lowered, but frequency accuracy deteriorates (error exceeds 2%)
Solution Approach 1:
The system performs preliminary frequency calibration using external synchronization pulses before normal operation. The frequency adjustment circuit pre-adjusts the oscillator frequency to match the target frequency, storing the calibration data for later use. This preliminary action enables the oscillator to achieve high accuracy (<2% error) without requiring continuous reference clocks during normal operation, thus reducing both cost and device complexity while maintaining frequency accuracy.
2Measurement precision
If external synchronization pulses are used for frequency adjustment, then frequency accuracy is improved, but device complexity increases due to additional circuitry
Solution Approach 1:
The invention extracts the frequency adjustment functionality into a separate, dedicated frequency adjustment circuit that operates independently during calibration. The main oscillator circuit remains simple and unchanged during normal operation. By separating the calibration function from the main oscillation function, the system achieves high frequency accuracy without significantly increasing the complexity of the core oscillator circuitry. The adjustment circuit only activates during brief calibration periods using external synchronization pulses.
3Measurement precision
If continuous reference clock feedback is implemented, then frequency accuracy is maintained, but energy consumption increases
Solution Approach 1:
Instead of continuous reference clock feedback, the system uses periodic external synchronization pulses for frequency calibration. The oscillator is adjusted at specific intervals using these pulses, then operates autonomously without continuous feedback. This periodic calibration approach maintains frequency accuracy while dramatically reducing energy consumption compared to continuous phase-locked loop operation. The oscillator runs freely between calibration events, consuming minimal energy.
Data Source
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Figure 3
Figure 4
AI summary
Oscillator circuitry is disclosed. The oscillator circuitry comprises a free-running oscillator (8) for generating pulses at a frequency, and a frequency adjustment circuit for adaptively adjusting the frequency of the free-running oscillator. The frequency adjustment circuit comprises a counter (15) configured to count a number (24) of pulses (22) generated by the free-running oscillator and logic (26) configured to compare the number of pulses with an expected number (25) of pulses (corresponding to a target frequency) to determine a difference value (29) and to adjust the frequency of the free-running oscillator in dependence on the difference value. The frequency adjustment circuit is configured, in response to receiving a synchronisation pulse (4; Fig. 3), to trigger an update of the number of pulses to be compared.