Crystal Oscillator Startup Using Self-Injected Frequency Feedback
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Solution Overview
Problem
Crystal oscillators with high quality factors take a long time to start up, which affects power consumption in small wireless devices, and existing frequency injection methods are not robust against environmental changes.
Innovation Solution
A crystal oscillator circuit using an amplifier-based frequency injection system that provides a self-injected frequency correlated with the crystal oscillator's frequency, with a two-stage operational amplifier for stability against environmental variations, and a dynamically adjustable load capacitance to reduce start-up time.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of time
If frequency injection is used to reduce start-up time, then start-up time is reduced, but the injection frequency may drift with environmental changes and become insufficiently close to the crystal oscillator frequency
Solution Approach 1:
The injection frequency generating circuit uses the crystal oscillator itself to generate the injection frequency through feedback. The circuit senses the output frequency of the crystal oscillator and feeds it back as the injection frequency, making the system self-calibrating and automatically adapting to environmental changes without external intervention.
Solution Approach 2:
The patent implements a feedback mechanism where the output frequency of the crystal oscillator is sensed and fed back to the injection frequency generating circuit. This feedback loop ensures that the injection frequency continuously tracks the actual oscillation frequency of the crystal, compensating for environmental drift and maintaining accurate frequency matching.
2Loss of time
If a driving oscillator generates a range of frequencies to encompass the crystal oscillator frequency, then start-up is facilitated, but the driving oscillator still needs calibration and adaptation
Solution Approach 1:
Instead of requiring external calibration, the injection frequency generating circuit automatically adjusts itself by using the crystal oscillator's own output frequency as the reference. The circuit senses the actual frequency and generates the injection frequency accordingly, eliminating the need for manual calibration or adaptation procedures.
3Use of energy by moving object
If the crystal oscillator operates in sleep mode for extended periods, then power consumption is reduced, but the start-up time becomes a significant portion of the active transmission time
Solution Approach 1:
The injection frequency generating circuit is pre-configured to immediately provide the correct injection frequency when power is applied. By having the frequency reference ready in advance (generated from the crystal's own output), the oscillator can start up much faster, reducing the warm-up time before data transmission can begin and thus improving overall transmission efficiency.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution significantly reduces the start-up time of the crystal oscillator while minimizing power consumption and maintaining robustness against environmental changes, such as temperature, voltage, and process variations.
Implementation Method 1
Frequency injection, i.e. providing an external frequency to activate the crystal oscillator, may reduce the start-up time of the crystal oscillator significantly
Implementation Method 2
with a two-stage operational amplifier for stability against environmental variations
Implementation Method 3
and a dynamically adjustable load capacitance to reduce start-up time
Data Source
Figure 1
Figure 2
Figure 3a~3b
AI summary
A crystal oscillator circuit (100) comprises: a crystal oscillator (102); and an injection frequency generating circuit (104), said injection frequency generating circuit (104) being configured to sense a signal of the crystal oscillator (102) and amplify the sensed signal, the injection frequency generating circuit (104) being further configured to inject the amplified signal to the crystal oscillator (102); wherein the crystal oscillator circuit (100) is configured such that the crystal oscillator (102) receives the amplified signal during an initial start-up period of the crystal oscillator (102) and stops receiving the amplified signal at an end of the initial start-up period.