Dual Temperature Compensation Oscillator for Low Phase Noise
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Solution Overview
Problem
Existing oscillators face challenges in reducing phase noise and improving frequency-temperature characteristics, particularly due to high-order temperature compensation processing that deteriorates noise characteristics and limits frequency variable sensitivity.
Innovation Solution
The oscillator incorporates a first temperature compensation circuit performing first-order processing and a second temperature compensation circuit performing high-order processing, allowing for selective mode settings to prioritize either noise reduction or frequency-temperature characteristic improvement, with the first circuit handling frequency-temperature characteristics of oscillation circuit elements and the second circuit handling those of the resonator, using a fractional-N type PLL for precise frequency adjustment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If high-order temperature compensation processing is performed in the oscillation loop, then frequency-temperature characteristics are improved, but phase noise near carrier frequency deteriorates
Solution Approach 1:
The temperature compensation processing is divided into two separate circuits: a first temperature compensation circuit that performs first-order compensation and a second temperature compensation circuit that performs high-order compensation. This segmentation allows each circuit to handle different aspects of temperature compensation, enabling high-order compensation without directly impacting the phase noise in the oscillation loop.
Solution Approach 2:
The first temperature compensation circuit acts as an intermediary between the resonator and the second temperature compensation circuit. It performs initial first-order compensation, reducing the burden on the second circuit and allowing the second circuit to focus on high-order compensation without introducing excessive noise into the oscillation loop.
2Measurement precision
If frequency variable sensitivity of the oscillation circuit is increased to compensate for frequency-temperature characteristics, then temperature compensation accuracy is improved, but phase noise is deteriorated
Solution Approach 1:
The compensation function is segmented between two circuits with different sensitivity characteristics. The first temperature compensation circuit operates with higher frequency variable sensitivity to achieve accurate first-order compensation, while the second circuit operates with lower sensitivity for high-order compensation, thus distributing the noise impact.
Solution Approach 2:
Different parts of the compensation system are designed with different local qualities: the first temperature compensation circuit is optimized for high sensitivity and first-order accuracy, while the second temperature compensation circuit is optimized for lower sensitivity and high-order accuracy. This local differentiation allows each circuit to perform its specific function optimally without compromising overall phase noise performance.
Data Source
AI summary
An oscillator includes a resonator, an oscillation circuit, and first and temperature compensation circuits. The first temperature compensation circuit performs a first-order first temperature compensation processing in a first mode and performs the first-order first temperature compensation processing and a high-order first temperature compensation processing in a second mode for a frequency of a first clock signal generated by oscillation of the resonator by the oscillation circuit. The second temperature compensation circuit receives the first clock signal and outputs a second clock signal subjected to a high-order second temperature compensation processing based on the first clock signal.