Receiver Equalizer Jitter Tolerance via Zero-Crossing Timing
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Solution Overview
Problem
Current receiver equalization techniques, such as those using the Least Mean Square (LMS) algorithm, are sub-optimal in addressing jitter and inter-symbol interference (ISI) issues, particularly under conditions of strong sinusoidal jitter and spread spectrum clocking, as they compromise the horizontal eye opening and tolerance to sinusoidal jitter.
Innovation Solution
The method involves sampling an analog signal at twice the baud rate to generate interleaved data and timing signals, calculating a timing error term for non-zero crossing transitions, and controlling the receiver equalizer based on this timing error term, rather than relying solely on zero-crossing transitions, to adapt the equalizer and improve eye opening robustness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional LMS algorithm is used for receiver equalization, then the equalizer can be controlled based on timing error detection, but the horizontal eye opening is compromised and tolerance to sinusoidal jitter is reduced
Solution Approach 1:
The patent inverts the conventional approach by using zero-crossing transitions (where the signal changes polarity) as the basis for timing error detection, rather than using the traditional method that relies on maximum amplitude points. This inversion allows the timing error term to be calculated from transitions that are less susceptible to sinusoidal jitter, thereby maintaining horizontal eye opening while improving jitter tolerance. The key insight is that zero-crossing points provide more stable timing references under jitter conditions.
Solution Approach 2:
The patent changes the parameter used for timing error calculation from amplitude-based metrics to transition-based metrics. By detecting timing errors at zero-crossing transitions rather than at peak amplitude points, the system adapts to jitter conditions differently. This parameter change enables the equalizer to maintain accurate timing synchronization even when sinusoidal jitter is present, thus preserving the horizontal eye opening.
2Measurement precision
If sampling is performed at twice the baud rate to obtain interleaved data and timing signals, then timing recovery can be improved, but the processing complexity increases
Solution Approach 1:
The patent segments the sampled signal into two interleaved sequences: data samples and timing samples. By sampling at twice the baud rate, the system creates alternating data and timing samples that can be processed independently. The timing samples are specifically used for timing error detection and equalizer control, while data samples are used for data recovery. This segmentation allows the system to dedicate specific samples to timing recovery functions, improving timing accuracy without requiring complex processing of the entire signal stream.
Solution Approach 2:
The high-rate sampled signal serves multiple functions simultaneously: data samples are used for both data recovery and timing error detection, while timing samples are used for timing synchronization and equalizer adaptation. This multi-functionality allows the system to extract maximum utility from the oversampled signal, improving timing recovery accuracy while minimizing the need for additional processing resources.
3Ease of manufacture
If equalizer adaptation is performed using conventional methods, then the system can operate with standard algorithms, but performance degrades under strong jitter and spread spectrum clocking conditions
Solution Approach 1:
The patent enables the equalizer to adapt itself automatically by using the zero-crossing transitions from the received signal to generate timing error terms. The system uses its own signal transitions as the reference for adaptation, eliminating the need for external calibration or complex training sequences. This self-service approach maintains implementation simplicity while significantly improving performance under jitter and spread spectrum clocking conditions, as the equalizer continuously adapts to the actual signal characteristics.
Data Source
AI summary
A receiver equalizer that provides improved jitter tolerance relative to common adaptation mechanisms and that also provides inter-symbol interference. Improved jitter tolerance is an important benefit for SERDES receivers as tolerance to Sinusoidal Jitter is an important performance metric specified in most industry standards.