USB RC Oscillator Calibration Using EOP and SYNC Timing

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Solution Overview

Problem

Existing frequency calibration methods for non-crystal oscillators in electronic products require additional costs due to the use of non-volatile memory programming or laser-trimming, which complicates manufacturing and testing processes.

Innovation Solution

A frequency calibration circuit and method that utilizes an end-of-packet and SYNC pattern of a low-speed Universal Serial Bus to automatically calibrate the frequency of a resistor-capacitor oscillator, eliminating the need for non-volatile memory and laser trimming by generating digital data from differential signals, counting clocks, and comparing them to predetermined values to adjust the oscillator's frequency.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Manufacturing precision

If non-volatile memory programming or laser-trimming is used to calibrate frequency, then frequency calibration accuracy is improved, but manufacturing cost and process complexity increase

Engineering Contradiction:

Improvefrequency calibration accuracyVSAvoidmanufacturing process complexity

Core Design Contradiction:

Manufacturing precisionVSDevice complexity

Solution Approach 1:

The system performs self-calibration by utilizing the USB communication interface and built-in counters to automatically measure and adjust oscillator frequency. The calibration process is executed autonomously during USB operation without requiring external programming equipment or laser-trimming facilities, thereby simplifying manufacturing while maintaining calibration accuracy.

Inventive Principle:

Principle #25Self-service

Solution Approach 2:

The USB interface serves multiple functions: data communication, device enumeration, and frequency calibration. By reusing the existing USB communication infrastructure for calibration purposes, the system eliminates the need for separate calibration hardware or processes, reducing overall device complexity while achieving accurate frequency calibration.

Inventive Principle:

Principle #6Universality (Multi-functionality)

2Manufacturing precision

If non-volatile memory programming or laser-trimming is used to calibrate frequency, then frequency calibration accuracy is improved, but additional manufacturing cost is incurred

Engineering Contradiction:

Improvefrequency calibration accuracyVSAvoidmanufacturing cost

Core Design Contradiction:

Manufacturing precisionVSEase of manufacture

Solution Approach 1:

Inventive Principle:

Principle #25Self-service

Solution Approach 2:

The system adjusts oscillator frequency by modifying operating parameters (such as resistor values or capacitor values) based on feedback from the USB communication timing measurements. This parameter-based adjustment approach replaces expensive physical trimming processes with software-controlled parameter modification, reducing manufacturing costs while achieving the desired frequency accuracy.

Inventive Principle:

Principle #35Parameter changes

3Device complexity

If USB communication is used for frequency calibration, then manufacturing process is simplified, but calibration precision may be affected by USB signal variations

Engineering Contradiction:

Improvemanufacturing process simplicityVSAvoidfrequency calibration precision

Core Design Contradiction:

Device complexityVSManufacturing precision

Solution Approach 1:

The system employs feedback mechanisms where the USB communication timing is measured, compared against reference values, and used to adjust the oscillator frequency. Multiple measurement cycles are performed to average out signal variations, and the calibration process iterates until the desired precision is achieved, thereby compensating for USB signal variations while maintaining manufacturing simplicity.

Inventive Principle:

Principle #23Feedback

Solution Approach 2:

The system performs multiple calibration measurements and iterations beyond the minimum single measurement, using accumulated data to improve precision. By performing excessive calibration actions (multiple cycles of measurement and adjustment), the system compensates for signal variations and achieves high calibration precision despite the simplicity of the USB-based approach.

Inventive Principle:

Principle #16Partial or excessive action

Data Source

PatentUS8634506B2Frequency calibration circuit for automatically calibrating frequency and method thereof

Publication Date: 2014.01.21 WELTREND SEMICON INC

AI summary

Generate a series of digital data according to a pair of differential signals received from a low speed universal serial bus. Calibrate coarsely a frequency of an oscillator according to a width of an end-of-packet of the series of digital data. And calibrate finely the frequency of the oscillator according to a width of a SYNC pattern of the series of digital data.