Crystal Oscillator Background Calibration for Stable GNSS Timing
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Solution Overview
Problem
Crystal oscillators without temperature or voltage compensation exhibit large frequency variations with temperature changes, leading to inaccuracies in GNSS positioning systems, which can prolong search times or cause failures.
Innovation Solution
A method for temperature-calibrating crystal oscillators in a background mode using wireless signals of known frequency, establishing a frequency-temperature relationship to achieve accurate frequency estimation at any given temperature, thereby compensating for frequency variations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a crystal oscillator without temperature or voltage compensation is used, then device complexity and cost are reduced, but frequency stability deteriorates with temperature changes
Solution Approach 1:
The system performs preliminary calibration of the crystal oscillator by measuring its frequency at multiple temperatures and storing calibration data before actual operation. This advance preparation allows the system to compensate for temperature variations without requiring complex real-time correction mechanisms, thus maintaining frequency stability while keeping the oscillator simple.
Solution Approach 2:
The system changes the operating parameters by measuring frequency at different temperatures and using these parameter variations to create a calibration model. This allows the simple oscillator to achieve stable frequency output by referencing pre-measured temperature-frequency relationships rather than using complex compensation circuitry.
2Stability of the object's composition
If a temperature-compensated crystal oscillator (TCXO) is used, then frequency stability is improved, but device complexity and cost increase
Solution Approach 1:
Instead of using a complex TCXO, the system creates a digital copy or model of the temperature-frequency relationship through calibration measurements. This calibration data model allows the system to estimate and compensate for frequency variations using simple calculations rather than complex hardware compensation circuits.
Solution Approach 2:
The system replaces the mechanical/electrical compensation mechanisms of a TCXO with a software-based calibration approach. By measuring frequency at various temperatures and using lookup tables or mathematical models, the system substitutes complex hardware compensation with simpler computational methods.
3Measurement precision
If calibration is performed before GNSS session launch, then measurement precision is improved, but time consumption increases
Solution Approach 1:
The calibration process is performed in advance before the GNSS session begins, allowing the system to prepare accurate frequency compensation data without interfering with the time-critical positioning operations. This preliminary calibration ensures measurement precision is optimized while the actual calibration time does not extend the GNSS session duration.
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.