Pierce Crystal Oscillator Voltage Matching Without Startup Loss
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Solution Overview
Problem
The challenge in crystal oscillator circuits is matching the supply voltage with the drive level of a quartz crystal, as separate companies design and manufacture amplifiers and crystals, leading to issues with oscillation margin and accelerated aging, particularly with high supply voltages and large mismatches, where traditional solutions like damping resistors reduce oscillation capabilities.
Innovation Solution
A Pierce oscillator circuit with a damping capacitor (C_d) acts as a capacitive voltage divider, reducing the supply voltage to match the drive level of the crystal without affecting the oscillation margin, by selecting capacitance to form a capacitive voltage divider, which is especially effective for large mismatches and high supply voltages.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a damping resistor is added to reduce the supply voltage to match the crystal drive level, then the supply voltage matching is improved, but the oscillation margin decreases and oscillation capabilities are affected
Solution Approach 1:
The patent changes the type of component used for voltage damping from a resistive element to a capacitive element. By introducing a damping capacitor instead of a damping resistor, the supply voltage is reduced to match the crystal drive level while the oscillation margin is preserved. The capacitor modifies the voltage distribution through capacitive division rather than resistive division, thereby resolving the contradiction between voltage matching and oscillation capability.
2Reliability
If a large damping resistor is used to reduce the supply voltage for large mismatches, then the supply voltage matching is improved, but the oscillation capabilities are severely reduced or oscillation may not start at all
Solution Approach 1:
The patent changes the damping mechanism from resistive to capacitive. The damping capacitor provides voltage reduction through capacitive division, which does not have the same detrimental effect on oscillation startup as large resistive damping. This parameter change allows the system to handle large voltage mismatches while maintaining reliable oscillation startup and operation.
3Duration of action of stationary object
If the supply voltage is reduced to match the crystal drive level, then the crystal aging is reduced, but the oscillation margin may be affected
Solution Approach 1:
The patent changes the damping component from resistive to capacitive, allowing supply voltage reduction to match crystal drive level specifications and reduce crystal aging. The capacitive damping mechanism achieves this voltage reduction without the negative side effects on oscillation margin that are associated with resistive damping, thereby extending crystal lifetime while maintaining oscillation performance.
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
This method effectively reduces the drive level of the crystal by a factor of 2 or more without diminishing the oscillation margin, suitable for small quartz crystals, high supply voltages, and scenarios where resistive damping is undesirable, ensuring the crystal operates within specified power consumption limits.
Implementation Method 1
The capacitor C d together with the load capacitor act as a capacitive voltage divider and the capacitance of this capacitor may be selected to reduce the supply voltage to match the drive level of the crystal oscillator
Data Source
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AI summary
A method and crystal oscillator circuit for matching a supply voltage with a drive level of a crystal are disclosed. The crystal oscillator circuit is based on a Pierce oscillator circuit which further comprises a capacitor Cd. The capacitor Cd together with the load capacitor act as a capacitive voltage divider and the capacitance of this capacitor may be selected to reduce the supply voltage to match the drive level of the crystal oscillator without affecting the oscillation margin of the crystal.