Programmable Clock Recovery Circuits for Adjacent Channel Leakage
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Solution Overview
Problem
In optical communication systems, especially in gridless deployments, increasing channel density is hindered by interchannel interference and clock jitter due to spectral energy leakage from adjacent channels, which affects the integrity of the extracted data clock and limits bandwidth utilization.
Innovation Solution
The proposed solution involves a programmable clock recovery circuit with a phase rotator and adjustable reference clock to decouple the clock recovery bandwidth from the receiver's phase noise suppression, allowing for optimized filtering of adjacent channel interference and improved phase noise suppression, thereby enhancing the accuracy of clock synchronization.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If channel density is increased to improve bandwidth utilization, then spectral efficiency is improved, but interchannel interference increases due to spectral energy leakage from adjacent channels
Solution Approach 1:
The patent segments the clock recovery process into two independent bandwidth domains: a wide receiver PLL bandwidth for phase noise suppression and a narrow clock recovery bandwidth for adjacent channel interference filtering. This segmentation allows simultaneous optimization of both phase noise performance and interference rejection, enabling increased channel density without compromising signal integrity.
Solution Approach 2:
The patent changes the bandwidth parameter of the clock recovery circuit to be programmable and adjustable, decoupling it from the fixed receiver PLL bandwidth. By dynamically adjusting the clock recovery bandwidth parameter, the system can optimize performance for different channel spacing configurations, allowing tighter channel packing while maintaining adequate interference filtering.
2Productivity
If guard bands are reduced to increase channel density, then spectral efficiency is improved, but clock jitter increases due to spectral energy leakage affecting the extracted data clock
Solution Approach 1:
The patent segments the frequency domain into two distinct functional regions: a wide receiver PLL bandwidth for suppressing phase noise from the voltage controlled oscillator, and a narrow clock recovery bandwidth for filtering adjacent channel interference. This segmentation enables the system to operate with reduced guard bands while maintaining clock synchronization accuracy through selective frequency filtering.
Solution Approach 2:
The patent introduces a programmable clock recovery bandwidth filter as an intermediary between the wideband receiver PLL output and the data sampling clock. This intermediary component selectively passes the desired clock signal while blocking adjacent channel interference, thereby protecting clock synchronization accuracy even when guard bands are minimized for increased channel density.
3Reliability
If clock recovery bandwidth is increased to improve clock tracking, then clock synchronization is improved, but adjacent channel interference increases affecting receiver performance
Solution Approach 1:
The patent segments the bandwidth requirements into two independent domains: a wide receiver PLL bandwidth for effective phase noise suppression and clock tracking, and a narrow clock recovery bandwidth for adjacent channel interference filtering. This segmentation resolves the contradiction by allowing each domain to be optimized independently for its specific function.
Solution Approach 2:
The patent makes the clock recovery bandwidth dynamically programmable and adjustable based on operating conditions and channel spacing configurations. This dynamic adjustment capability allows the system to optimize the trade-off between clock tracking performance and interference rejection for different deployment scenarios, maintaining reliable clock synchronization while minimizing adjacent channel interference effects.
Data Source
AI summary
Techniques and circuits are proposed to increase averaging in the clock recovery band based on an amount of channel overlap in receivers using excess bandwidth for clock recovery, to mitigate the impact of spectral energy leaking into an active channel of interest from an adjacent active channel and to improve the accuracy of the phase estimate of the received transmitted clock.