Crystal Frequency Compensation Using Piecewise PLL Divider Control
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Solution Overview
Problem
Existing electronic systems face challenges in accurately compensating for temperature-dependent frequency errors in crystal reference signals, particularly due to limited memory capacity and computational efficiency, which restricts effective temperature compensation beyond stored values.
Innovation Solution
Implementing a piecewise linear temperature compensation approximation method that computes a temperature compensation value using a few stored data values, allowing for efficient adjustment of the division ratio in a phase-locked loop's fractional divider to compensate for temperature-induced frequency errors, thereby maintaining a stable output frequency across varying temperatures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a relatively large amount of memory is used to store temperature compensation data, then temperature compensation accuracy is improved, but device complexity and cost increase
Solution Approach 1:
The patent divides the temperature compensation function into discrete segments corresponding to different temperature ranges. Each segment has associated compensation values stored in memory, allowing the system to use only the relevant segment for the current temperature condition. This segmentation reduces the total memory required compared to storing all possible temperature compensation data continuously.
Solution Approach 2:
The patent changes the parameter of memory storage from storing complete temperature compensation curves for all conditions to storing only discrete compensation values for specific temperature ranges. By changing how the compensation data is parameterized and stored, the system achieves adequate compensation accuracy with significantly reduced memory requirements.
2Device complexity
If temperature compensation data is stored in limited memory, then device complexity is reduced, but temperature compensation accuracy deteriorates
Solution Approach 1:
The patent applies partial action by storing only the essential temperature compensation values needed for the operating temperature range, rather than storing complete compensation data for all possible temperatures. The system stores a subset of compensation data that is sufficient to achieve the required accuracy specification (e.g., 2-3 ppm) without the overhead of comprehensive memory storage.
3Adaptability or versatility
If crystal frequency error is compensated over a wide temperature range, then adaptability is improved, but memory requirements increase
Solution Approach 1:
The patent segments the wide temperature range into multiple discrete temperature ranges, each with its own compensation values. This allows the system to cover a broad temperature spectrum while storing only the minimal necessary data for each segment, reducing total memory requirements compared to storing continuous compensation data across the entire range.
Data Source
AI summary
One embodiment relates to a method of compensating for crystal frequency variation over temperature. An example method includes obtaining an indication of temperature, computing a temperature compensation value based on the indication of temperature and a piecewise linear temperature compensation approximation, and compensating for a temperature offset in a crystal reference signal by adjusting a division ratio of a fractional divider in a phase-locked loop. The piecewise linear temperature compensation approximation can represent an approximation of frequency error in a crystal reference signal originating from a crystal over temperature. The piecewise linear temperature compensation approximation can be, for example, a linear approximation, a quadratic approximation, or a cubic approximation.