Receiver Constellation Switching for Stable PAM2-to-PAM4 Training
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Solution Overview
Problem
The transition from 2-level pulse amplitude modulation (PAM2) to 4-level pulse amplitude modulation (PAM4) in Fibre Channel standards can magnify timing jitter and impair adaptation, unduly delaying or preventing the completion of the link training phase.
Innovation Solution
Implement receivers that adapt gain or filter coefficients during PAM2 signaling, switch to PAM4 detection before receiving PAM4 signaling, and enable adaptation after detection, using adjusted PAM4 detection values to facilitate a graceful transition.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If adaptive gain control and filter coefficient adaptation are performed during the transition from PAM2 to PAM4 signaling, then the receiver can optimize its equalization filters and decision thresholds, but timing jitter is magnified and adaptation is impaired
Solution Approach 1:
The patent applies preliminary action by completing the adaptation of gain and filter coefficients during PAM2 signaling before transitioning to PAM4 signaling. This ensures that the equalization filters and decision thresholds are fully optimized for the current signaling mode before the transition occurs, preventing timing jitter magnification that would result from attempting adaptation during the transition phase.
Solution Approach 2:
The link training process is segmented into distinct phases: PAM2 signaling with adaptation, transition phase, and PAM4 signaling. By separating the adaptation process from the transition phase, the patent avoids the timing jitter issues that arise when adaptation is attempted during constellation switching, while still achieving optimal equalization before PAM4 operation begins.
2Productivity
If the transition from PAM2 to PAM4 signaling is performed during link training, then higher data transfer rates are achieved, but the link training phase may be unduly delayed or prevented from completing
Solution Approach 1:
The patent performs preliminary adaptation of all necessary parameters (gain, filter coefficients) during PAM2 signaling before the transition to PAM4. This preliminary optimization ensures that when the transition occurs, the receiver is already configured optimally, preventing delays that would otherwise occur during PAM4 adaptation and ensuring smooth transition to high-speed operation.
Solution Approach 2:
The patent skips the adaptation phase during the PAM4 transition by completing all adaptation beforehand during PAM2 signaling. This allows the transition to PAM4 to occur rapidly without the time-consuming adaptation process that would otherwise delay link training completion, enabling the system to reach high data transfer rates efficiently.
3Adaptability or versatility
If adaptation is enabled during PAM4 detection transition, then the receiver can optimize for PAM4 signaling, but timing jitter is magnified and adaptation is impaired
Solution Approach 1:
The patent enables preliminary adaptation during PAM2 signaling to optimize gain and filter coefficients before the PAM4 transition. This preliminary optimization ensures that when PAM4 detection begins, the receiver is already adapted to the signal characteristics, improving both the stability and speed of PAM4 detection without the timing jitter issues that would result from concurrent adaptation during transition.
Data Source
AI summary
Accordingly, there are disclosed herein receivers and receiving methods that provide a graceful transition from PAM2 to PAM4 signaling. One illustrative method includes: negotiating a link speed having PAM4 signaling; performing adaption of at least one gain or filter coefficient during PAM2 signaling; switching to PAM4 detection before receiving PAM4 signaling; disabling said adaptation before said switching to PAM4 detection; detecting PAM4 signaling using at least one statistic of detected PAM4 symbols; and enabling said adaptation after PAM4 signaling is detected. Another illustrative method includes: negotiating a link speed having PAM4 signaling; adapting at least one of gain and filter coefficients during PAM2 signaling; monitoring for a change in at least one signal characteristic while performing PAM2 detection; and transitioning to PAM4 detection after detecting said change.