Temperature-Compensated Crystal Oscillator Filtering for Low Phase Noise
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Solution Overview
Problem
Existing oscillation devices using temperature-compensated crystal oscillators face issues with phase noise due to inconsistent temperature detection and correction, leading to unstable output frequencies and increased circuit size to mitigate these problems.
Innovation Solution
An oscillation device that incorporates a temperature detection system, an accumulator, a rounding processing unit, and a digital filter to accumulate and smooth the temperature data, allowing for gradual frequency correction and reducing phase noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a cumulative averaging circuit with a large accumulation number is used to reduce variations in temperature detection value, then the phase noise is reduced, but the accumulation time increases causing significant frequency correction changes and phase error
Solution Approach 1:
The patent changes the parameter of accumulation number from a fixed large value to a dynamically adjustable value. The accumulation number is set based on the absolute value of frequency correction: when |frequency correction| ≥ threshold, accumulation number = first value (smaller); when |frequency correction| < threshold, accumulation number = second value (larger). This dynamic parameter adjustment resolves the contradiction by adapting the accumulation time to current temperature change conditions.
2Productivity
If a cumulative averaging circuit with a small accumulation number is used to reduce accumulation time, then the response speed is improved, but variations in temperature detection value and frequency correction become significant aggravating phase noise
Solution Approach 1:
The patent dynamically adjusts the accumulation number parameter based on temperature change conditions. When temperature changes are small (|frequency correction| < threshold), a larger accumulation number is used to reduce phase noise. When temperature changes are large (|frequency correction| ≥ threshold), a smaller accumulation number is used to improve response speed. This resolves the contradiction by making the accumulation number adaptive to current operating conditions.
3Reliability
If the accumulation number in the cumulative averaging circuit is increased to reduce phase noise, then the temperature detection value stability is improved, but the circuit complexity increases
Solution Approach 1:
The patent introduces dynamic control of the accumulation number based on temperature change conditions. Instead of using a fixed large accumulation number that would always guarantee stability, the system dynamically selects between a first accumulation number and a second accumulation number based on whether |frequency correction| ≥ threshold. This dynamic approach maintains stability when needed while reducing circuit complexity requirements when temperature changes are large.
Data Source
AI summary
An oscillation device corrects a setting value of an output frequency based on a detection result of an ambient temperature of a crystal unit. The oscillation device includes: an oscillation circuit; a temperature detection portion that detects the ambient temperature and outputs a digital value corresponding to the temperature detection value; an accumulator that accumulates the digital value; a rounding processing portion that performs rounding for the digital value accumulated in the accumulator; a digital filter that receives the digital value obtained from the rounding processing portion and obtains a step response gradually increasing from “0” and converging to a step value; and a correction value obtaining portion that obtains a frequency correction value of the oscillation frequency of the oscillation circuit caused by a difference between the ambient temperature and a reference temperature, wherein the setting value of the output frequency is corrected based on the frequency correction value.