Temperature-Compensated Synthesizer Switching With Low Phase Noise
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Solution Overview
Problem
Conventional synthesizers experience significant phase noise and deterioration in Carrier-to-Noise (C/N) performance when switching frequency division ratios, particularly due to temperature changes, leading to potential reception failures in digital television and other applications.
Innovation Solution
A synthesizer design that includes a comparator and a controller to adjust the frequency division ratio without resetting the frequency divider, maintaining the past cumulative addition value to minimize changes in the output frequency and reduce phase noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the frequency division ratio is changed by resetting the accumulator, then the frequency division ratio switching is achieved, but the phase noise deteriorates and C/N performance decreases
Solution Approach 1:
The patent applies preliminary action by pre-calculating and storing the relationship between temperature changes and frequency division ratios in a lookup table. When temperature changes occur, the system retrieves the pre-determined frequency division ratio from the table rather than resetting and recalculating, thus avoiding phase noise while achieving the required frequency adjustment
Solution Approach 2:
The system implements feedback by continuously monitoring the temperature sensor output and dynamically adjusting the frequency division ratio based on the temperature-compensated values stored in the lookup table. This closed-loop approach ensures the VCO frequency remains stable despite temperature variations, preventing phase noise deterioration
2Manufacturing precision
If the accumulator is reset when switching frequency division ratios, then the correct frequency division is achieved, but the output frequency changes significantly causing reception failures
Solution Approach 1:
The patent changes the parameter being adjusted from a hard reset of the accumulator to a gradual adjustment of the frequency division ratio based on temperature-compensated lookup table values. This parameter change approach allows the system to achieve accurate frequency division while maintaining output frequency stability by making incremental adjustments rather than abrupt resets
Data Source
AI summary
A synthesizer including an oscillator for outputting an oscillation signal based on an output signal from a comparator, a frequency divider for dividing a frequency of an output signal from the oscillator based on control from a controller, and a temperature sensor for detecting an error between a preset frequency and a frequency based on a reference oscillation signal. The comparator compares an output signal from the frequency divider with an output signal from a MEMS oscillator and outputs a signal indicating the comparison result to the oscillator. The controller changes the frequency division ratio of the frequency divider based on an output signal from the temperature sensor and changes the frequency division ratio in a state in which the frequency division ratio is kept at the past value. Thus, phase noise deterioration in the synthesizer can be suppressed.