Frequency Generator with Segmented Feedback Loops for Phase Noise Reduction
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Solution Overview
Problem
Existing frequency generator circuits lack controllability and are prone to phase noise due to single feedback loops, making them unsuitable for demanding applications.
Innovation Solution
A frequency generator system incorporating a frequency ratio generator, comparator, controlled oscillator circuit, and outer loop filter, which uses a digital PLL and phase acquisition circuit to stabilize the frequency and reduce phase noise by separating noise sources and implementing temperature and hysteresis compensation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single feedback loop is used in the frequency generator circuit, then the circuit structure is simple, but all noise sources in the loop contribute to the phase noise of the output frequency
Solution Approach 1:
The patent divides the single feedback loop into multiple separate feedback loops (first feedback loop and second feedback loop). Each loop handles specific noise sources independently, allowing selective filtering of noise contributions to the output frequency. This segmentation enables the system to maintain simplicity while reducing overall phase noise by distributing noise management across multiple specialized loops.
2Speed
If the loop filter bandwidth is increased to track changes faster, then the response speed improves, but more noise sources are transmitted to the output
Solution Approach 1:
The patent implements separate feedback loops with different bandwidth characteristics. The first feedback loop is designed with a bandwidth optimized for tracking frequency changes rapidly, while the second feedback loop has a narrower bandwidth that filters out high-frequency noise sources. This segmentation allows the system to achieve fast response without transmitting excessive noise to the output.
Solution Approach 2:
The patent introduces intermediate filtering stages in the feedback loops that act as mediators between the high-bandwidth tracking function and the low-noise requirement. These intermediate filters selectively pass desired frequency tracking signals while attenuating noise components, enabling the system to reconcile the contradiction between response speed and noise reduction.
3Adaptability or versatility
If frequency control is added to the generator, then the frequency becomes controllable, but the circuit complexity increases
Solution Approach 1:
The patent employs feedback mechanisms in the frequency generator circuit that allow controllable frequency adjustment without proportionally increasing complexity. The feedback loops automatically adjust circuit parameters to maintain the desired output frequency, reducing the need for complex manual control circuits while achieving versatile frequency control capability.
Data Source
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AI summary
Generating a signal having a controlled frequency can be a useful electronic building block in different electronic circuits with very diverse functionalities.The current invention is a frequency generator for generating a controlled signal having a controlled frequency, comprising: a frequency ratio generator arranged for generating a frequency ratio, comprising: an input configured for receiving the controlled signal; a first controlled frequency divider (110) arranged for generating a first divided signal (115) having a first divided frequency being substantially the controlled frequency divided by a first frequency ratio signal; a converter arranged for generating an excitation signal (129) having the first divided frequency based on the first divided signal, wherein the excitation signal is provided to the resonator for excitation of the resonator; a resonator arranged for generating a resonance signal having a first resonance frequency, wherein the resonator is excited by the excitation signal; a first frequency phase detector (150) arranged for generating a first phase difference signal (155) based on a first frequency phase difference between the first divided frequency and the first resonance frequency; a first inner loop filter (160) arranged for generating the first frequency ratio signal;and an output configured for providing a frequency ratio signal based on the first frequency ratio signal indicative of the frequency ratio between the controlled frequency and the first resonance frequency; wherein a first frequency ratio generator loop is formed by the first controlled frequency divider, the first divided signal, the first frequency phase detector, the first phase difference signal, the first inner loop filter and the first frequency ratio signal; wherein a second frequency ratio generator loop is formed by the first controlled frequency divider, the first divided signal, the converter, the excitation signal, the resonator, the resonance signal, the first frequency phase detector, the first phase difference signal, the first inner loop filter and the first frequency ratio signal; wherein the first inner loop filter filters the first phase difference signal such that instability of the frequency ratio generator loops are prevented; and wherein the frequency generator further comprises: a comparator arranged for generating a comparison signal based on the comparison of the frequency ratio with a target ratio; and a controlled oscillator circuit comprising: connectors for connecting an oscillator for generating an oscillating signal having an oscillator frequency; and a PLL arranged for generating the controlled signal having the controlled frequency based on the oscillating frequency, wherein the oscillator frequency is adapted based on the comparison signal.