Clock Synthesizer Calibration With Temperature Compensation
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Solution Overview
Problem
Existing clock generation technologies face challenges in maintaining frequency accuracy over process, voltage, and temperature variations, particularly in portable devices where size and cost are concerns, and require impractical multi-point calibrations.
Innovation Solution
A one-point calibration and temperature-compensated scheme using a clock synthesizer, temperature sensor, non-volatile memory, and fractional-N phase-locked loop to adjust the clock frequency, minimizing the need for extensive calibration and maintaining accuracy across PVT variations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a crystal oscillator is used to generate an accurate clock, then frequency accuracy is improved, but device size and cost increase
Solution Approach 1:
The patent uses a ring oscillator to generate a clock signal that copies the function of a crystal oscillator, but with smaller size and lower cost. The ring oscillator is calibrated to match the frequency accuracy of a crystal oscillator without requiring the physical crystal component
Solution Approach 2:
The patent replaces the expensive crystal oscillator with a cheaper ring oscillator implementation using standard CMOS circuitry. The calibration process enables the cheaper component to achieve the performance of the expensive component
2Measurement precision
If multi-point calibration is performed to maintain frequency accuracy over PVT variations, then frequency accuracy is improved, but testing cost and complexity increase
Solution Approach 1:
The patent performs calibration at only one operating point (one-point calibration) rather than multiple points. This partial calibration approach, combined with temperature compensation, provides sufficient frequency accuracy without the excessive complexity of multi-point calibration
Solution Approach 2:
The patent implements a temperature sensor that provides feedback about the current temperature to a temperature compensated frequency controller. This feedback loop enables the system to adjust for temperature variations and maintain frequency accuracy without requiring calibration at every possible temperature point
3Device complexity
If one-point calibration is performed, then calibration complexity is reduced, but frequency accuracy deteriorates under PVT variations
Solution Approach 1:
The temperature sensor continuously monitors temperature and provides feedback to the frequency controller, which adjusts the oscillator frequency in real-time to compensate for temperature drift. This feedback mechanism maintains frequency accuracy despite performing calibration at only one point
Solution Approach 2:
The patent changes the operating parameters of the ring oscillator dynamically based on temperature measurements. By adjusting capacitance values or other oscillator parameters in response to temperature changes, the system maintains frequency accuracy across varying conditions without requiring multi-point calibration
Data Source
AI summary
Methods and apparatus are provided in the present invention to adjust the frequency of an output clock close to within a required accuracy of an oscillation frequency. In another embodiment, a method comprises: entering a calibration mode; generating a first control word to control a timing of a clock synthesizer; adjusting the first control word until the timing of the clock synthesizer is sufficiently accurate with respect to a timing of a reference clock; sensing a temperature using a temperature sensor; storing a present value of an output of the temperature sensor and the first control word into a non-volatile memory; exiting the calibration mode; entering a normal operation mode; sensing the temperature using the temperature sensor; generating a second control word to control the timing of the clock synthesizer in accordance with an output of the non-volatile memory and the output of the temperature sensor.