Dual-Loop Frequency Generator Using Resonator Ratio Control
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Solution Overview
Problem
Existing frequency generator circuits lack controllability over a wide frequency range and are prone to phase noise due to single feedback loops, making them unsuitable for demanding applications.
Innovation Solution
A frequency generator with a dual-loop feedback system, comprising a frequency ratio generator and a controlled oscillator, which allows for the generation of controlled frequencies with low phase noise by comparing the frequency ratio to a target ratio and using a comparator and loop filters to stabilize the 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 performance deteriorates due to all noise sources contributing to the output frequency
Solution Approach 1:
The patent divides the feedback system into two separate feedback loops: an inner loop for frequency control and an outer loop for phase noise reduction. The inner loop uses a frequency divider and phase detector to control the VCO frequency, while the outer loop uses a second phase detector and filter to further reduce phase noise. This segmentation allows each loop to address specific noise sources independently, improving overall phase noise performance without excessive complexity.
Solution Approach 2:
The patent introduces an intermediary frequency divider in the feedback path that divides the VCO output frequency by a factor N before feeding it back to the phase detector. This intermediary element allows the system to control the VCO at a lower frequency while maintaining the desired output frequency, thereby reducing the bandwidth requirements and phase noise contribution from the feedback loop components.
2Speed
If the loop filter bandwidth is increased to track frequency changes quickly, then the response speed is improved, but the phase noise performance deteriorates due to insufficient damping of noise sources
Solution Approach 1:
The patent segments the filtering function into two stages: an inner loop filter that allows higher bandwidth for fast frequency acquisition and locking, and an outer loop filter that provides lower bandwidth for noise suppression. This dual-stage filtering approach enables the system to achieve both fast response and low phase noise by assigning different bandwidth requirements to different parts of the feedback system.
3Stability of the object's composition
If a resonator is used to generate a stable frequency, then the frequency stability is improved, but the frequency controllability deteriorates because the resonator frequency cannot be controlled over a wide range
Solution Approach 1:
The patent introduces a voltage-controlled oscillator (VCO) as an intermediary between the control signal and the resonator. The VCO can be tuned over a wide frequency range by applying different control voltages, while the resonator provides frequency stabilization. This intermediary allows the system to achieve both wide frequency tunability and frequency stability by combining the advantages of both components.
Solution Approach 2:
The patent changes the operating parameters of the resonator by controlling the VCO frequency to match the resonator's resonance frequency. By adjusting the VCO control voltage, the system can lock onto different resonator modes or harmonics, thereby achieving wide frequency controllability while maintaining the frequency stability provided by the resonator.
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 dual-loop system enables the generation of controlled frequencies with low phase noise (less than 500 fs) over a wide range, improving stability and adaptability, and reducing noise rejection, thus enhancing the accuracy and temperature stability of the frequency output.
Implementation Method 1
a resonator arranged for generating a resonance signal having a first resonance frequency, wherein the resonator is excited based on the controlled signal
Data Source
AI summary
A frequency generator for generating a controlled signal having a controlled frequency uses a frequency ratio generator with an input; a frequency divider for dividing the controlled frequency by a frequency ratio signal to generate a divided signal having a divided frequency; a converter for generating an excitation signal having the divided frequency, the excitation signal exciting a resonator for generating a resonance signal having a resonance frequency; a frequency phase detector of a phase difference between the divided frequency and the resonance frequency; an inner loop filter for generating the frequency ratio signal and filtering the phase difference signal to prevent instability of two frequency ratio generator loops; an output configured for providing the frequency ratio signal based on a ratio between the controlled frequency and the resonance frequency; and a controlled oscillator circuit for generating the controlled signal based on comparison of the frequency ratio with a target ratio.