Internal Oscillator Frequency Compensation Using a Fixed Capacitor
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Solution Overview
Problem
Internal oscillators in devices often experience frequency deviations due to temperature and voltage changes, which existing bandgap-type circuits fail to adequately compensate, and using external crystal oscillators increases complexity and reduces efficiency.
Innovation Solution
A frequency compensation circuit adjusts the internal oscillator frequency based on a current calibration count and a target calibration count of a fixed capacitor, determined by measuring and interpolating diode voltage values at different temperatures, allowing for precise frequency adjustment without modifying the device's hardware.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If bandgap-type circuits are used to compensate oscillator frequency, then frequency stability is improved, but frequency deviation remains more than 1%
Solution Approach 1:
The patent changes the parameter being compensated from voltage (bandgap circuits) to capacitance. By measuring the capacitance of a fixed capacitor at different temperatures and voltages, and using these measurements to adjust the oscillator frequency, the system achieves better than 0.5% frequency accuracy across temperature and voltage variations, overcoming the limitation of bandgap circuits.
2Measurement precision
If external crystal oscillators are used to improve frequency accuracy, then frequency deviation is reduced, but device complexity increases
Solution Approach 1:
The patent replaces the mechanical/physical crystal oscillator with an electronic solution using a fixed capacitor and digital processing. Instead of relying on the physical resonant properties of a crystal, the system uses capacitance measurement and digital frequency adjustment to achieve the same frequency stability, thereby reducing analog complexity while maintaining accuracy.
Solution Approach 2:
The patent creates a digital model of the fixed capacitor's behavior across temperature and voltage conditions by measuring its capacitance at various points and storing these values in a lookup table. This digital copy allows the system to compensate for environmental variations without needing physical compensation circuits, simplifying the overall architecture.
3Device complexity
If internal oscillators are used to maintain simplicity, then device complexity is reduced, but frequency deviation reaches 2.5%
Solution Approach 1:
The patent implements a feedback mechanism where the capacitance of a fixed capacitor is measured under current temperature and voltage conditions, compared against pre-stored reference values, and used to generate a correction signal that adjusts the oscillator frequency. This closed-loop feedback enables the simple internal oscillator to achieve high frequency accuracy without external components.
Data Source
AI summary
A frequency compensation circuit determines a target calibration count of a fixed capacitor coupled to a processing device. The frequency compensation circuit identifies a current calibration count of the fixed capacitor. The frequency compensation circuit determines that the current calibration count satisfies a threshold criterion associated with the target calibration count. In response to determining that the current calibration count satisfies the threshold criterion, the frequency compensation circuit adjusts a frequency of an internal oscillator of the processing device based on the current calibration count and the target calibration count.