Crystal Oscillator Feedback Control for High-G GPS Frequency Stability
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Solution Overview
Problem
Crystal oscillators in GPS systems of high-spin aerospace devices are susceptible to G-forces, causing frequency shifts that lead to navigation errors due to the difficulty in detecting and compensating for these shifts using current techniques.
Innovation Solution
A method involving the measurement of G-forces, determination of frequency shifts, and temperature adjustment using a compensation circuit and oven to maintain a desired frequency, utilizing accelerometer and temperature measurement signals and stored relationship tables.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If temperature compensation is used to correct frequency shifts, then frequency stability is improved, but device complexity increases due to additional temperature control components
Solution Approach 1:
The patent implements a feedback control system where the accelerometer continuously monitors G-forces acting on the crystal oscillator, and the compensation circuit adjusts the oven temperature based on this feedback signal. The feedback voltage from the accelerometer is processed to generate a compensation voltage that modulates the oven heater, creating a closed-loop system that automatically corrects frequency shifts caused by acceleration.
Solution Approach 2:
The patent changes the temperature parameter of the crystal oscillator to compensate for frequency shifts. By adjusting the oven temperature based on the feedback from the accelerometer, the system dynamically modifies the operating temperature to counteract the effects of G-forces on the crystal's resonant frequency.
2Measurement precision
If acceleration compensation is implemented, then navigation accuracy is improved, but energy consumption increases due to continuous monitoring and adjustment
Solution Approach 1:
The patent combines the acceleration sensing function and frequency compensation function into an integrated system. The accelerometer serves dual purposes: monitoring the mechanical stress on the crystal and providing the feedback signal for temperature compensation. This merging reduces the need for separate compensation components and optimizes energy usage by coordinating the operation of the accelerometer and oven control.
3Measurement precision
If G-force measurement is continuously performed, then frequency shift compensation accuracy is improved, but device complexity and power consumption increase
Solution Approach 1:
The accelerometer in the patent serves multiple functions: it measures G-forces acting on the crystal oscillator, generates a feedback voltage proportional to acceleration, and provides input for the compensation circuit. This multi-functional use of the accelerometer reduces the need for additional sensing components and simplifies the overall system architecture while maintaining high compensation accuracy.
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 effectively compensates for G-force-induced frequency shifts in crystal oscillators, ensuring accurate timing and navigation by maintaining a stable frequency, thereby improving the precision of GPS systems in high-acceleration environments.
Implementation Method 1
measuring G-forces asserted on the crystal oscillator
Implementation Method 2
changing the temperature of the crystal oscillator based on the determined temperature to shift the crystal oscillator's frequency
Data Source
AI summary
Methods and apparatus for controlling frequency in a crystal oscillator are provided that allows for continued reception of GPS signal solution in a continuous high G environment. One method comprises measuring G-forces asserted on the crystal oscillator, determining a shift in frequency of the crystal oscillator due to the measured G-forces, determining a temperature that would shift the crystal oscillator's frequency back to a rate that would occur without the measured G-forces, and changing the temperature of the crystal oscillator based on the determined temperature to shift the crystal oscillator's frequency back to a rate that would occur if the G-forces were not present.