Dual-Loop Frequency Generator for Low Phase Noise Control
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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 with a frequency ratio generator, comparator, and controlled oscillator, along with an outer loop filter and phase acquisition circuit, which determines and stabilizes the frequency ratio between the controlled frequency and resonance frequencies, and compensates for temperature and hysteresis effects, ensuring a stable and controlled output.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single feedback loop is used in the frequency generator circuit, then the circuit complexity is reduced, but the phase noise increases due to all noise sources in the loop contributing to the output frequency
Solution Approach 1:
The patent divides the feedback loop into two separate loops: an inner feedback loop for frequency stabilization and an outer feedback loop for phase noise reduction. The inner loop uses a frequency divider and phase detector to stabilize the output frequency, while the outer loop uses a phase detector and loop filter to reduce phase noise by comparing the divided output signal with a reference signal. This segmentation allows each loop to address specific performance requirements independently.
Solution Approach 2:
The patent introduces an intermediary frequency divider that divides the output frequency by a factor N before feeding it back to the phase detector. This intermediary element enables the system to compare the output frequency with a reference signal at a lower frequency, reducing the bandwidth requirements and allowing for better noise filtering while maintaining frequency stability.
2Speed
If the loop filter bandwidth is increased to track changes in the loop, then the response speed improves, but the phase noise increases due to insufficient damping of noise sources
Solution Approach 1:
The patent segments the feedback system into two loops with different bandwidths: the inner loop has a wider bandwidth for fast frequency tracking, while the outer loop has a narrower bandwidth for effective noise filtering. This allows the system to maintain both fast response capability and low phase noise performance simultaneously.
Solution Approach 2:
The patent implements dual feedback loops where the outer loop provides additional phase noise reduction feedback. The outer loop compares the divided output signal with a reference signal and adjusts the oscillator frequency to minimize phase noise, while the inner loop maintains frequency stability. This layered feedback approach allows optimal bandwidth selection for each loop's specific function.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The system provides a highly stable controlled frequency with low phase jitter, effectively filtering out disturbances and maintaining stability across temperature variations, making it suitable for demanding applications such as telecommunications and navigation systems.
Implementation Method 1
a resonator, having a resonance frequency
Implementation Method 2
a phase acquisition circuit, having a first input and a second input and an output, arranged for determining a phase difference between a first input signal and a second input signal
Implementation Method 3
arranged for dampening disturbances in a feedback signal
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 divers 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 the frequency ratio signal based on a 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 arranged for generating the controlled signal having the controlled frequency based on the comparison signal.