Crystal Oscillator Background Calibration for Stable GNSS Frequency
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Solution Overview
Problem
Crystal oscillators without temperature or voltage compensation experience significant frequency variations with temperature changes, leading to inaccuracies in GNSS positioning systems, which can cause prolonged searches or failure in GNSS operations.
Innovation Solution
A method for temperature-calibrating crystal oscillators in a background mode using wireless signals of known frequency, determining the temperature-calibration status and initiating a calibration session when necessary, to establish a precise frequency-temperature relationship and compensate for frequency variations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a crystal oscillator without temperature or voltage compensation is used, then the device complexity and cost are reduced, but the frequency stability and positioning accuracy deteriorate significantly
Solution Approach 1:
The system performs preliminary temperature calibration of the crystal oscillator by measuring its frequency at multiple temperatures and storing calibration data before actual GNSS operation begins. This advance preparation allows the oscillator to be compensated for temperature variations without requiring complex hardware circuits, resolving the contradiction between simple oscillator design and frequency stability.
Solution Approach 2:
The system changes the operational parameters of the crystal oscillator by applying frequency correction based on measured temperature and stored calibration data. Instead of using a physically complex temperature-compensated oscillator, the system adjusts the frequency parameter through software calculation, achieving stable frequency output while maintaining simple hardware design.
2Measurement precision
If temperature calibration is performed continuously, then the frequency estimation accuracy is improved, but the energy consumption and processing time increase
Solution Approach 1:
The system performs temperature calibration periodically rather than continuously, initiating calibration sessions based on trigger conditions such as device boot, temperature thresholds, or GNSS operation start. This periodic approach maintains frequency estimation accuracy while significantly reducing energy consumption compared to continuous calibration.
Solution Approach 2:
The system performs temperature calibration in advance before GNSS positioning operations begin, so that when positioning is needed, the frequency correction data is already available. This preliminary calibration ensures high measurement precision during actual use without requiring continuous energy-intensive calibration processes.
3Adaptability or versatility
If the crystal oscillator frequency varies with temperature, then the device can operate across different temperatures, but the positioning accuracy and search efficiency deteriorate
Solution Approach 1:
The system implements feedback by continuously monitoring the crystal oscillator frequency at different temperatures and using this information to calculate correction factors. The measured frequency deviations are fed back into the positioning algorithm to compensate for temperature effects, allowing the device to maintain high positioning accuracy across varying temperatures without sacrificing temperature adaptability.
Data Source
AI summary
System and method for temperature-calibration of a crystal oscillator (XO) in a mobile device. A temperature-calibration status of the XO is determined and a trigger condition related to temperature-calibration of the XO is detected. If the temperature-calibration status of the XO is not fully temperature-calibrated or if the XO has not been previously temperature-calibrated, a temperature-calibration session is initiated by an XO manager based on the condition, wherein a receiver is configured to receive signals and temperature-calibration of the XO is performed in a background mode based on the received signals. The condition based triggering ensures that the XO is temperature-calibrated prior to launch of any position based or global navigation satellite systems (GNSS) based applications on the mobile device. The trigger condition can include first use or power-on, charging, presence in an outdoor environment, variation in operating temperature, pre-specified time, and/or user input pertaining to the mobile device.