Differential Adaptive-Bandwidth PLL for Low-Noise Wide-Range Locking
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Solution Overview
Problem
Conventional phase locked loops (PLLs) face challenges in achieving stable operation across wide frequency ranges due to issues with loop bandwidth and damping factor, leading to instability and errors from noise sources like supply and substrate noise, while existing adaptive bandwidth solutions are complex and require significant die space.
Innovation Solution
A fully differential adaptive bandwidth phase locked loop with differential supply regulation, incorporating a differential charge pump, active loop filter and regulator, and voltage-controlled oscillator, which maintains a constant loop bandwidth-to-frequency ratio and damping factor over a wide range, reducing noise susceptibility and increasing jitter performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a large loop bandwidth is used to reduce input tracking jitter and allow locking to a wide range of reference signal frequencies, then the PLL can lock to a wider frequency range with reduced jitter, but off-frequency noise encroaches into the PLL operation introducing errors
Solution Approach 1:
The patent implements adaptive bandwidth control where the loop bandwidth dynamically adjusts based on the operating frequency. The loop bandwidth is set to a first value when the PLL operates at a first frequency range and changes to a second value when operating at a second frequency range. This dynamic adjustment allows the PLL to maintain optimal performance across a wide frequency range while filtering out noise at each specific operating point.
Solution Approach 2:
The patent changes the loop bandwidth parameter adaptively based on the operating frequency. By monitoring the operating frequency and adjusting the loop bandwidth accordingly, the system optimizes the trade-off between tracking performance and noise rejection at different frequency points, ensuring both wide frequency range capability and high operating accuracy.
2Adaptability or versatility
If a damping factor that varies with operating frequency is used, then the PLL can operate at different frequencies, but errors are introduced into the operating frequency limiting its utility to a narrow operating frequency range
Solution Approach 1:
The patent dynamically adjusts the damping factor based on the operating frequency range. The system monitors the operating frequency and changes the damping factor to appropriate values for each frequency range, ensuring stable operation and accurate frequency generation across the entire operating range without the errors associated with fixed or improperly varying damping factors.
Solution Approach 2:
The damping factor is changed adaptively according to the operating frequency. The patent implements different damping factor values for different frequency ranges, optimizing the PLL's transient response and stability characteristics at each operating point while maintaining high frequency accuracy throughout the operating range.
3Reliability
If adaptive bandwidth loop filter implementations are used to maintain loop bandwidth following operating frequency and keep damping factor constant, then input noise is limited without limiting operating frequency range, but the implementation becomes complex and requires large die space
Solution Approach 1:
The patent combines the loop filter and regulator into an integrated adaptive bandwidth loop filter implementation. This merged structure achieves noise filtering and bandwidth adaptation in a unified circuit, reducing the overall complexity and die space requirements compared to separate implementations while maintaining the ability to limit input noise across the operating frequency range.
Solution Approach 2:
The adaptive bandwidth loop filter serves multiple functions simultaneously: it filters input noise, adapts the loop bandwidth to the operating frequency, and maintains a constant damping factor. This multi-functional design reduces the need for separate circuits for each function, thereby reducing overall circuit complexity and die space while achieving superior noise performance.
4Adaptability or versatility
If conventional adaptive bandwidth implementations are used, then loop bandwidth follows operating frequency, but other sources of errors such as supply noise and substrate noise are not fully addressed
Solution Approach 1:
The patent introduces a regulator as an intermediary component between the charge pump and the loop filter. This regulator cleans the supply voltage by filtering out supply noise and substrate noise before it reaches the sensitive loop filter and VCO circuits. The regulator acts as a mediator that protects the PLL from external noise sources while maintaining the adaptive bandwidth functionality.
Solution Approach 2:
The patent converts the harmful effect of supply noise and substrate noise into a benefit by using the regulator to identify and filter these noise sources. The regulator monitors the supply voltage and actively compensates for noise variations, turning the previously harmful noise into an opportunity for enhanced noise filtering and improved overall PLL performance across the frequency range.
Data Source
AI summary
Provided is a fully differential adaptive bandwidth phase locked loop with differential supply regulation. One fully differential phase locked loop includes a differential active loop filter and regulator coupled to an output of a differential charge pump, a differential voltage-controlled oscillator coupled to differential control voltages developed by the differential active loop filter and regulator, and a bias circuit coupled to the differential control voltages and providing a bias current to the differential charge pump.