USB Oscillator Calibration Using SOF Period Counting
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Solution Overview
Problem
Conventional calibrated oscillators for USB devices require complex calibration methodologies due to fabrication process deviations and temperature variations, often necessitating bulky external resonators that increase costs and occupy space, especially in low-cost and miniature devices.
Innovation Solution
A calibration unit comprising a counting and comparing unit and a control circuit that adjusts the oscillator frequency based on deviations determined from the number of oscillation periods between characteristic data traffic instances, such as SOF tokens, allowing for on-chip oscillator calibration without external resonators.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If an external precise resonator (quartz or ceramic) is used to achieve high oscillator accuracy, then the oscillator accuracy is improved, but the device size and cost increase
Solution Approach 1:
The patent extracts the calibration function from external components and implements it within the oscillator circuit itself using a calibration unit that counts oscillation periods and adjusts calibration parameters, eliminating the need for external resonators while maintaining accuracy
Solution Approach 2:
The oscillator circuit is designed to perform multiple functions: generating the clock signal and simultaneously calibrating itself through the integrated calibration unit that responds to host device signals, replacing the need for separate external calibration components
2Measurement precision
If an external precise resonator is used to achieve high oscillator accuracy, then the oscillator accuracy is improved, but the device cost increases
Solution Approach 1:
The patent removes the expensive external resonator component and replaces it with an integrated calibration mechanism that uses software-based frequency adjustment, significantly reducing bill of materials cost while maintaining USB compliance accuracy requirements
Solution Approach 2:
The patent uses a cost-effective integrated oscillator with digital calibration instead of expensive external resonators, accepting that the oscillator frequency can be adjusted through calibration parameters rather than relying on precision passive components
3Measurement precision
If conventional calibration methodology is used with multiple temperature measurements, then the oscillator accuracy across temperatures is improved, but the calibration complexity and manufacturing cost increase
Solution Approach 1:
The patent performs calibration during the manufacturing process by measuring the oscillator frequency at a single reference temperature and storing compensation parameters, eliminating the need for complex multi-temperature calibration procedures while achieving accurate temperature compensation
Solution Approach 2:
The patent changes the calibration approach from multi-temperature frequency measurements to single-temperature measurement with stored compensation parameters that are applied during operation, significantly simplifying the calibration process while maintaining accuracy
Data Source
AI summary
Disclosed is a calibration unit for calibrating an oscillator of a device comprises a counting and comparing unit and a control circuit. The counting and comparing unit is configured to determine a number of periods of a clock signal lying between a starting instance and an ending instance. Therein, the clock signal is generated by the oscillator. The counting and comparing unit is further configured to determine a deviation of the number of periods from a reference number. The control circuit is configured to adjust the oscillator depending on the deviation.