PLL Phase Slope Limiting Without Losing Frequency Tracking
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Solution Overview
Problem
Existing phase locked loops (PLLs) face challenges in maintaining precise phase and frequency slope limits, leading to slowdowns in response time and instability when dealing with tight synchronization requirements, particularly in applications like Timing over Packet switched networks, where phase and frequency changes need to be managed within stringent criteria.
Innovation Solution
The introduction of a method that modifies the proportional component of the phase error signal using a non-linear saturation function and an exponential decaying function, while keeping the integral component unchanged, allows for constant phase slope limiting and frequency tracking, ensuring that phase and frequency variations adhere to user-programmed limits without compromising response time or stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the proportional part is significantly over-limited to meet phase slope limit, then phase slope limit is satisfied, but PLL response time slows down
Solution Approach 1:
The patent implements dynamic phase slope limiting by switching between two modes: a first limiting mode that applies aggressive limiting only when phase error exceeds a threshold (prior to lock), and a second mode that applies gentle limiting after lock is achieved. This dynamic adaptation allows the system to satisfy phase slope limits during critical transitions while maintaining fast response during normal operation.
Solution Approach 2:
The patent applies excessive limiting action only when necessary (when phase error exceeds threshold) and uses partial limiting (gentle slope limit) during normal operation. This selective application of limiting strength ensures phase slope compliance without unnecessarily slowing down the PLL response during stable operation.
2Manufacturing precision
If the integral part is frozen to maintain phase slope limit, then phase slope limit is satisfied, but frequency tracking capability is lost
Solution Approach 1:
The patent segments the phase slope limiting function into two independent parts: proportional part limiting and integral part limiting. The proportional part is limited when phase error exceeds threshold, while the integral part continues to accumulate without freezing. This segmentation allows phase slope compliance while preserving frequency tracking capability through the integral component.
Solution Approach 2:
The patent applies partial limiting to the proportional part while leaving the integral part unrestricted. This selective limiting approach satisfies phase slope requirements through proportional control without compromising the integral part's frequency tracking function.
3Manufacturing precision
If constant phase slope limiting is applied, then phase slope precision is improved, but frequency changes cannot be followed
Solution Approach 1:
The patent implements dynamic phase slope limiting with two distinct thresholds: a first threshold for aggressive limiting when phase error is large, and a second threshold for gentle limiting after lock. This dynamic structure provides precise phase slope control during critical transitions while allowing frequency tracking during stable operation.
Solution Approach 2:
The patent applies excessive limiting precision only when phase error exceeds the first threshold, and uses partial limiting with a second threshold during normal operation. This ensures precise phase slope control when needed while maintaining frequency tracking capability.
Data Source
AI summary
Phase slope is controlled in a phase locked loop wherein a phase error signal controlling a controlled oscillator has a proportional component and an integral component, by determining whether the proportional component falls within a range bounded by upper and lower limit values. The proportional component is combined with the integral component if the proportional component falls within the range to provide the phase error signal. Otherwise, the proportional component is modified to meet a phase slope requirement while leaving the integral component unmodified. The modified proportional component is combined with the unmodified integral component to provide the phase error signal.