Retimer Equalizer Training During Link Speed Negotiation
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Solution Overview
Problem
Retimers with adaptive equalizers face challenges in supporting communication protocols with different signal constellations and symbol rates, particularly during link speed negotiation, where high baud rates lead to extended link training times and potential performance degradation due to sudden signaling speed changes and spectral deficiencies.
Innovation Solution
The implementation of retimer modules and methods that include an analog-to-digital converter, equalizer, clock recovery module, and adaptation module, which digitize receive signals, derive sampling clocks based on equalization errors, and enable coefficient updates only during stable conditions, ensuring adequate equalization and minimizing performance degradation during link speed negotiation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If retimers perform equalizer training at high baud rates during link speed negotiation, then communication speed is improved, but link training time is extended beyond the module response time
Solution Approach 1:
The patent performs equalizer training before link speed negotiation is complete, during the module response time period. By preparing the equalizer coefficients in advance at lower speeds, the system avoids the need for extensive training when transitioning to higher baud rates, thus resolving the contradiction between achieving high communication speed and minimizing link training time.
Solution Approach 2:
The patent dynamically adjusts the equalizer training process based on the current baud rate and link conditions. The equalizer coefficients are updated adaptively during link speed negotiation, allowing the system to optimize performance at each speed transition while maintaining training within the module response time constraints.
2Reliability
If retimers update equalizer coefficients continuously during link speed negotiation, then equalization performance is improved, but system stability deteriorates due to sudden signaling speed changes
Solution Approach 1:
The patent prevents harmful effects by disabling equalizer coefficient updates during periods of unstable link conditions or sudden baud rate changes. This preliminary protective measure avoids the instability that would result from updating coefficients when the signal characteristics are rapidly changing, thus maintaining system stability while preserving equalization performance during stable periods.
Solution Approach 2:
The patent implements a feedback mechanism that monitors link stability and baud rate transitions. Based on this feedback, the system intelligently controls when to enable or disable equalizer updates, ensuring that coefficient updates only occur when link conditions are stable enough to support reliable equalization, thereby balancing performance and stability.
3Device complexity
If retimers use a fixed sampling clock frequency, then clock recovery simplicity is improved, but adaptability to different baud rates deteriorates
Solution Approach 1:
The patent employs a single fixed-frequency sampling clock that serves multiple baud rates through oversampling. This universal clock approach simplifies the clock recovery architecture while maintaining adaptability to different symbol rates, as the fixed clock can accommodate various baud rates by adjusting the sampling relationship rather than requiring separate clocks for each rate.
Data Source
AI summary
Disclosed retimer modules and methods enable equalizer training during link speed negotiation. One illustrative retimer module includes: an analog to digital converter that uses a sampling clock to digitize a receive signal; an equalizer that converts the digitized receive signal into an equalized signal; a decision element that derives a receive symbol stream from the equalized signal; and a clock recovery module that derives the sampling clock based at least in part on an equalization error of the equalized signal, the sampling clock having a frequency with a range including a baud rate of the receive signal at a first supported speed and including a frequency not less than twice the baud rate of the receive signal at a second supported speed.