Crystal-oscillator circuit
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Solution Overview
Problem
Conventional crystal-oscillator circuits face challenges in stabilizing output frequency during startup due to heat generation, temperature compensation errors, and parasitic elements, making it difficult to achieve high accuracy and stability, especially in electronic devices with increasing data rates and power efficiency requirements.
Innovation Solution
Incorporating a second variable-capacitance element group and a time constant circuit that generates a signal with a predetermined time constant to stabilize the output frequency by compensating for temperature characteristics and adjusting capacitance values, thereby reducing frequency changes during startup before reaching a steady state.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If power supply is turned on to start oscillation, then oscillation frequency is generated, but heat generation causes temperature change and frequency instability during startup period
Solution Approach 1:
The patent applies preliminary action by pre-configuring the time constant circuit to generate a control signal that anticipates and compensates for temperature changes during startup. The circuit prepares the capacitance adjustment mechanism before the temperature drift actually occurs, allowing the oscillation frequency to remain stable throughout the warm-up period rather than drifting as conventional circuits experience.
2Stability of the object's composition
If temperature compensation circuit is added to stabilize frequency, then temperature characteristic is compensated, but device complexity increases
Solution Approach 1:
The patent merges the temperature compensation function with the existing oscillation circuit by integrating the time constant circuit into the feedback path. Rather than adding a completely separate temperature compensation subsystem, the invention combines multiple functions (frequency stabilization, temperature compensation, and startup control) into a unified circuit architecture that shares common components and signal paths, thereby reducing overall complexity.
Solution Approach 2:
The time constant circuit automatically generates the appropriate control signal based on the inherent time constant of the RC network, eliminating the need for external temperature sensors, microcontrollers, or complex compensation algorithms. The circuit self-regulates the capacitance value in response to temperature changes through its intrinsic electrical characteristics, providing autonomous temperature compensation without additional control infrastructure.
3Adaptability or versatility
If variable capacitance element is used to adjust frequency, then output frequency can be tuned, but frequency changes during temperature transition periods
Solution Approach 1:
The patent implements feedback by connecting the time constant circuit in a feedback path that continuously monitors the oscillation state and automatically adjusts the capacitance value of the variable capacitance element. This closed-loop control ensures that any frequency deviations caused by temperature changes are detected and corrected in real-time, maintaining stable output frequency while preserving the ability to tune the frequency through the variable capacitance mechanism.
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 solution effectively stabilizes the output frequency during startup and before steady-state oscillation, improving the startup characteristic and frequency stability of crystal-oscillator circuits, which is crucial for high-accuracy and low-power consumption in modern electronic devices.
Implementation Method 1
a time constant circuit configured to generate a time constant signal which changes with a predetermined time constant
Implementation Method 2
a MOS variable-capacitance element 60 whose capacitance value changes depending on a control voltage
Implementation Method 3
A quartz crystal unit generally exhibits a temperature characteristic approximated by a cubic function
Data Source
AI summary
In a crystal-oscillator circuit having a quartz crystal unit, further stabilization of output frequency change at a time of startup of the power supply is achieved. A crystal-oscillator circuit having a quartz crystal unit includes a first variable-capacitance element, which forms an oscillation loop with the quartz crystal unit, and a temperature compensation circuit which provides a first control signal for the first variable-capacitance element to compensate for a temperature characteristic of the quartz crystal unit. In addition, the crystal-oscillator circuit includes a second variable-capacitance element group, and a time constant circuit which provides a time constant signal, which changes with a predetermined time constant, for the second variable-capacitance element group as a second control signal.