Crystal Oscillator Background Calibration for GNSS Temperature Drift
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Solution Overview
Problem
Crystal oscillators without temperature or voltage compensation (XO) experience significant frequency variations with temperature changes, leading to inaccuracies in GNSS positioning, which existing technologies have not adequately addressed due to cost and size constraints.
Innovation Solution
A method for temperature-calibrating crystal oscillators in a mobile device using wireless signals of known frequency, allowing for the determination of a precise frequency-temperature relationship, enabling accurate frequency estimation at any given temperature and compensating for frequency variations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a crystal oscillator without temperature or voltage compensation (XO) is used, then cost and device size are reduced, but frequency stability and positioning accuracy deteriorate due to significant frequency variations with temperature changes
Solution Approach 1:
The system performs preliminary temperature calibration of the XO by comparing its frequency output against known reference frequencies from GNSS satellites or terrestrial sources at different temperatures. This calibration data is stored and used to compensate for frequency variations during operation, allowing the use of cheaper XO components while maintaining accuracy
Solution Approach 2:
The system continuously monitors the XO's frequency output and compares it against expected values based on temperature and calibration data. When deviations are detected, the system applies corrective frequency adjustments, creating a closed-loop feedback mechanism that maintains frequency stability without requiring expensive compensated oscillators
2Device complexity
If a crystal oscillator without temperature or voltage compensation (XO) is used, then device complexity is reduced, but positioning accuracy deteriorates due to large frequency variations across temperature
Solution Approach 1:
The system performs preliminary temperature calibration of the XO by comparing its frequency output against known reference frequencies from GNSS satellites or terrestrial sources at different temperatures. This calibration data is stored and used to compensate for frequency variations during operation, allowing the use of cheaper XO components while maintaining accuracy
Solution Approach 2:
The system changes the operational parameters of the XO by adjusting its frequency output based on temperature and calibration data. The frequency tuning mechanism modifies the XO's operating point to compensate for temperature-induced drift, maintaining positioning accuracy without increasing device complexity
3Measurement precision
If temperature calibration is performed using known wireless signals, then frequency estimation accuracy is improved, but time consumption increases due to the calibration process
Solution Approach 1:
The system performs the time-consuming temperature calibration process in advance, during device initialization or when the device is first powered on. The calibration results are stored for future use, so subsequent positioning operations can proceed quickly without repeating the full calibration sequence
Solution Approach 2:
The system performs temperature calibration periodically based on trigger conditions such as significant temperature changes, device wake-up from sleep mode, or when positioning accuracy is compromised. This periodic approach balances calibration accuracy needs with time efficiency, avoiding unnecessary repeated calibrations
Data Source
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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.