Injection Oscillator Recalibration for Fast Crystal Oscillator Start-Up
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Solution Overview
Problem
Existing clock circuits face challenges in achieving precise frequency accuracy for injection oscillators used to kick-start crystal oscillators, leading to prolonged start-up times and increased power consumption due to the limitations of frequency accuracy and sensitivity to temperature and component aging.
Innovation Solution
A digital frequency calibration circuit is introduced to recalibrate the injection frequency of the injection oscillator, using digital control signals to maintain high accuracy by periodically updating the injection frequency to match the resonant frequency of the crystal oscillator, accounting for temperature and voltage variations, and utilizing digital elements to minimize power consumption and design complexity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of time
If an injection oscillator is used to kick-start a crystal oscillator, then the start-up time of the crystal oscillator is reduced, but the frequency accuracy of the injection oscillator deteriorates (typically around 1-2% when temperature variation and component aging are considered)
Solution Approach 1:
The patent applies preliminary action by pre-calibrating the injection oscillator frequency to match the crystal oscillator resonant frequency before the kick-start operation. A calibration circuit measures the actual resonant frequency of the crystal oscillator and adjusts the injection oscillator frequency accordingly in advance, ensuring that when the injection occurs, the frequency match is within ±0.5% even accounting for temperature variation and component aging. This preliminary frequency alignment resolves the contradiction by preparing the system in advance to achieve both fast start-up and high frequency accuracy.
Solution Approach 2:
The patent implements feedback through a calibration circuit that continuously monitors and adjusts the injection oscillator frequency based on the actual crystal oscillator resonant frequency. The calibration circuit measures the resonant frequency and generates correction signals to maintain frequency alignment within ±0.5%. This feedback mechanism ensures that frequency accuracy is maintained despite temperature variation and component aging, while still enabling fast kick-start operation.
2Loss of time
If the injection frequency is maintained very close to the resonant frequency (within ±0.5% or ±0.25%), then the start-up time is further reduced, but the sensitivity to temperature variation and component aging increases
Solution Approach 1:
The calibration circuit provides continuous feedback to maintain injection frequency within ±0.5% of the resonant frequency despite temperature variation and component aging. The circuit measures actual frequency drift and generates correction signals to compensate, ensuring both fast start-up and long-term frequency stability.
Solution Approach 2:
The patent changes the operating parameters of the injection oscillator dynamically through calibration. By adjusting the injection frequency parameter to precisely match the resonant frequency (within ±0.5%) and maintaining this alignment through temperature and aging compensation, the system achieves both reduced start-up time and improved frequency stability over time.
3Measurement precision
If a digital frequency calibration circuit is used to maintain high frequency accuracy, then the frequency accuracy improves (maintained within ±0.5%), but the device complexity increases
Solution Approach 1:
The patent replaces complex analog frequency tuning mechanisms with a digital frequency calibration circuit. The digital circuit uses counters, comparators, and digital-to-analog converters to achieve precise frequency alignment within ±0.5%, simplifying the overall design while improving frequency accuracy compared to traditional analog tuning methods.
Solution Approach 2:
The calibration circuit is designed to be self-calibrating, automatically measuring the crystal oscillator resonant frequency and adjusting the injection oscillator frequency without external intervention. This self-service capability reduces the need for manual calibration and complex external tuning equipment, thereby reducing overall system complexity while maintaining high frequency accuracy.
4Use of energy by moving object
If the crystal oscillator is turned off during low power sleep modes, then the power consumption is reduced, but the start-up time increases when the crystal oscillator needs to be restarted
Solution Approach 1:
The system performs preliminary calibration of the injection oscillator frequency before entering sleep mode. When the crystal oscillator needs to be restarted from sleep mode, the pre-calibrated injection oscillator can immediately kick-start the crystal oscillator with high frequency accuracy, minimizing start-up time while maintaining low power consumption during sleep mode.
Solution Approach 2:
The calibration is performed periodically or on-demand rather than continuously, allowing the system to maintain low power consumption during sleep modes while ensuring frequency accuracy is maintained when the crystal oscillator is restarted. The periodic calibration approach balances power savings with the need for accurate frequency alignment.
Data Source
AI summary
Embodiments of clock circuits disclosed herein include a crystal oscillator circuit, an injection oscillator coupled to kick-start the crystal oscillator circuit and a digital frequency calibration circuit coupled to recalibrate the injection oscillator. The crystal oscillator circuit is configured to generate a clock signal at a resonant frequency. The injection oscillator is coupled to supply an oscillation signal at an injection frequency to the crystal oscillator circuit to reduce a start-up time of the crystal oscillator circuit. The digital frequency calibration circuit is coupled to receive the resonant frequency and the injection frequency as inputs, and configured to supply a digital control signal to the injection oscillator to set the injection frequency of the injection oscillator substantially equal to the resonant frequency of the crystal oscillator circuit. Methods are provided herein to recalibrate the injection frequency of an injection oscillator over time, temperature and/or supply voltage.