Sub-Rate Receiver Equalizer With Lane Mismatch Adaptation
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Solution Overview
Problem
High-speed optical and electrical receivers face challenges with shrinking data bit periods and tightening timing margins, leading to stringent clocking and receiver timing requirements, which are exacerbated by random and systematic mismatches between sub-rate lanes, resulting in suboptimal signal-to-noise ratio (SNR) and bit error rate (BER) performance.
Innovation Solution
A mismatch adaptive sub-rate receiver architecture is introduced, where larger digital-to-analog converters (DACs) are shared across sub-rate receiver lanes, and smaller DACs are used for each lane to account for lane-specific offsets and mismatches, with an adaptation engine generating control signals to optimize signal processing and reduce inter-symbol interference (ISI).
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of time
If sub-rate receiver architectures are used to relax timing requirements, then timing margin is improved, but lane mismatch causes suboptimal SNR
Solution Approach 1:
The receiver is segmented into multiple independent sub-rate lanes, each with its own equalizer and decision circuitry. This allows each lane to be optimized independently for timing recovery while maintaining overall system performance through parallel processing of the incoming high-speed signal.
Solution Approach 2:
Each sub-rate lane is equipped with lane-specific equalizer coefficients and decision thresholds that are locally optimized to compensate for lane-specific mismatches and impairments. This local optimization ensures that each lane achieves optimal SNR despite variations across lanes.
2Area of stationary object
If larger DACs are shared across sub-rate lanes, then area efficiency is improved, but lane-specific mismatch cannot be compensated
Solution Approach 1:
Multiple sub-rate lanes share common high-speed analog front-end components including the photodetector, transimpedance amplifier, and coarse DAC. This merging of components reduces overall semiconductor area while maintaining the ability to compensate for lane-specific mismatches through per-lane equalization.
Solution Approach 2:
The shared coarse DAC serves multiple sub-rate lanes simultaneously, providing a universal interface for digital control of the analog front-end. This multi-functional component reduces area overhead while per-lane fine DACs provide the necessary specificity for mismatch compensation.
3Reliability
If per-lane DACs are used to compensate for lane mismatch, then SNR is improved, but semiconductor area increases
Solution Approach 1:
The DAC functionality is segmented into two hierarchical levels: a shared coarse DAC that provides common control for all lanes, and per-lane fine DACs that provide lane-specific compensation. This segmentation allows area-efficient implementation while maintaining the SNR benefits of per-lane optimization.
Solution Approach 2:
The DAC resolution and range are changed based on the specific needs of each lane. The shared coarse DAC uses lower resolution for common control, while per-lane fine DACs use higher resolution only where needed for mismatch compensation, optimizing the area-performance tradeoff.
Data Source
AI summary
A receiver is provided that includes a plurality of sub-rate receiver lanes each of which is configured to receive an analog receive signal from an analog front-end and produce digital sub-rate receiver data. The receiver includes one or more first digital-to-analog converters (DACs) (also referred to herein as “average” DACs) shared across the plurality of sub-rate receiver lanes, and one or more second DACs (also referred to herein as “mismatch cancellation” DACs) for each sub-rate receiver lane of the plurality of sub-rate receiver lanes. The one or more second DACs of a respective sub-rate receiver lane provide output to be combined with an output of a corresponding one of the one or more first DACs during processing of the analog receive signal in the respective sub-rate receiver lane to account for a sub-rate receiver lane specific offset with respect to a corresponding one of the one or more first DACs.