Quartz Oscillator Temperature Control Using Frequency Difference
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Solution Overview
Problem
Conventional oven controlled crystal oscillators (OCXO) face challenges in maintaining high-frequency stability over a wide temperature range due to variations and aging of analog components, making them unsuitable for applications requiring high-stability clock signals at a low cost, such as base stations and repeater stations.
Innovation Solution
A quartz-crystal controlled oscillator system that includes two quartz-crystal oscillators with distinct electrodes on a common quartz-crystal piece, a frequency difference detecting unit, and a circuit that controls a heating unit based on temperature detection to maintain a constant atmosphere temperature, using the frequency difference between the oscillators as a temperature detection value and integrating this value to stabilize the oscillation output.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If discrete analog parts (operational amplifier, resistance, capacitor) are used for temperature control in OCXO, then temperature control structure is simple, but frequency stability deteriorates due to variation and aged deterioration of parts
Solution Approach 1:
The patent replaces the mechanical/analog temperature control system (using operational amplifiers, resistors, and capacitors) with a digital control system. The frequency difference detection unit measures temperature through frequency differences between two quartz-crystal oscillators, and the control unit processes this digital information to regulate the heating unit, eliminating analog components and their associated drift and aging issues.
Solution Approach 2:
The patent introduces two quartz-crystal oscillators as intermediary sensing elements. Instead of directly measuring temperature with analog sensors, the system uses the frequency difference between two oscillators as an indirect measure of temperature, which is then fed to the digital control unit for processing and heating regulation.
2Measurement precision
If two quartz-crystal oscillators are adjusted to satisfy f0≈f1≈f2 for frequency compensation, then temperature compensation accuracy is improved, but manufacturing process becomes complicated and yield decreases
Solution Approach 1:
The patent employs two quartz-crystal oscillators that inherently exhibit frequency-temperature characteristics. The system utilizes the natural frequency difference between these oscillators as a self-generating temperature indicator, eliminating the need for external temperature sensors and complex adjustment procedures. The oscillators themselves provide the temperature information needed for control.
Solution Approach 2:
The patent changes the measurement parameter from direct temperature measurement to frequency difference measurement. By monitoring the frequency difference between two oscillators, which varies with temperature, the system achieves temperature detection without requiring precise frequency matching during manufacturing, thereby simplifying the production process.
3Measurement precision
If clocks from respective quartz-crystal oscillators are counted for a given period to determine frequency difference, then temperature detection is achieved, but detection time increases and accuracy is compromised
Solution Approach 1:
The patent uses periodic oscillation signals from the quartz-crystal oscillators directly for temperature detection. Instead of counting clock pulses over an extended period, the system leverages the inherent periodic frequency signals of the oscillators, which can be processed rapidly by the frequency difference detection unit to determine temperature with minimal delay.
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 approach achieves high-stability oscillation output by accurately controlling the atmosphere temperature, enhancing the frequency stability of the quartz-crystal controlled oscillator and reducing the complexity of the manufacturing process, thereby addressing the limitations of conventional OCXO systems.
Implementation Method 1
a first quartz-crystal oscillator structured by providing first electrodes on a quartz-crystal piece; a second quartz-crystal oscillator structured by providing second electrodes on a quart-crystal piece
Implementation Method 2
controlling an electric power supplied to the heating unit based on the partial difference obtained in the adding section
Data Source
AI summary
An atmosphere temperature at which a quartz-crystal oscillator and an oscillation circuit are placed is controlled in high accuracy, and an output frequency with high stability is obtained. If oscillation outputs of first and second quartz-crystal oscillators are set to f1 and f2, and oscillation frequencies of the oscillation outputs at a reference temperature are set to f1r and f2r, respectively, {(f2−f1)/f1}−{(f2r−f1r)/f1r} is calculated by a frequency difference detection unit. A digital value can be obtained by representing this value by 34-bit digital value, corresponding to a temperature. Therefore, this value is treated as a temperature detection value, a difference with a temperature set value is supplied to the loop filter, and the digital value therefrom is converted into a direct-current voltage to control a heater.