Hybrid Subordinate Clock With Three-Loop Servo Noise Filtering
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Solution Overview
Problem
Existing packet-based timing systems face challenges in achieving precise timing synchronization over packet-switched networks, particularly in maintaining frequency stability and reducing noise interference from multiple reference signals.
Innovation Solution
A three-loop servo system is implemented, comprising a first servo loop for the physical layer, a second servo loop for the intermediate layer, and a third servo loop for the grandmaster reference, each with digitally controlled oscillators and phase-locked loop structures, to attenuate noise across different frequency bands and align the subordinate clock with the grandmaster clock.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If multiple reference signals are used in packet-based timing systems, then timing flexibility and adaptability are improved, but noise interference and frequency stability deteriorate
Solution Approach 1:
The timing system is divided into three separate servo loops, each handling a specific reference signal (physical layer reference, intermediate reference, and grandmaster reference). This segmentation allows each loop to process and filter its designated reference independently, preventing noise accumulation from multiple references while maintaining the flexibility to use all three sources.
Solution Approach 2:
The intermediate clock signal serves as a mediator between the physical layer reference and the grandmaster reference. The second servo loop generates this intermediate signal that combines characteristics from both references, acting as a buffer that reduces direct noise interaction between the two primary reference sources while maintaining timing flexibility.
2Measurement precision
If multiple servo loops are implemented, then frequency accuracy and noise filtering are improved, but device complexity increases
Solution Approach 1:
The three servo loops are merged into a single integrated timing system where the output of one loop feeds into the next. The first servo loop processes the physical layer reference and feeds the second loop, which processes the intermediate reference and feeds the third loop that handles the grandmaster reference. This merging allows noise filtering to accumulate across loops while maintaining a unified system architecture rather than separate independent systems.
Solution Approach 2:
The servo loops are nested in a hierarchical structure where the first servo loop is contained within the timing system, the second servo loop is nested within the same system processing the intermediate signal, and the third servo loop is nested processing the grandmaster reference. This nesting allows each loop to operate at a different hierarchical level, managing complexity through structured organization rather than flat architecture.
3Object-affected harmful factors
If three-loop servo system is used, then noise attenuation across frequency bands is improved, but device complexity increases
Solution Approach 1:
Each servo loop is designed with specific local characteristics optimized for its function: the first servo loop is optimized for physical layer reference processing with appropriate bandwidth filtering, the second servo loop is optimized for intermediate signal processing, and the third servo loop is optimized for grandmaster reference synchronization. This local quality optimization allows each loop to effectively attenuate noise in its specific frequency range without requiring all loops to be over-engineered, reducing overall complexity.
Solution Approach 2:
The servo loops employ dynamic bandwidth adjustment and adaptive filtering where each loop can dynamically adjust its response characteristics based on the quality and stability of its reference signal. This dynamic behavior allows the system to optimize noise attenuation in real-time without requiring a fixed complex structure, as the loops adapt their complexity based on actual operating conditions rather than being statically over-designed.
Data Source
AI summary
A subordinate clock includes a first servo loop, a second servo loop, and a third servo loop, each include a respective digitally controlled oscillator (DCO). The first DCO receives (i) a first error signal that is associated with a physical layer reference signal and (ii) an oscillating signal and outputs a physical layer clock signal. The second DCO receives (i) a second error signal associated with the physical layer clock signal and (ii) the oscillating signal and outputs an intermediate clock signal. The third DCO receives (i) a third error signal associated with a grandmaster reference signal generated by a grandmaster clock and (ii) the intermediate clock signal and outputs a final clock signal with an average frequency that is generally equal to an average frequency of the grandmaster reference signal.