Multi-Wire Bus Skew Calibration with Composite MIC Measurements
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Solution Overview
Problem
In high-speed chip-to-chip communication systems, differential signal arrival times across multiple wires cause skew, which can prevent coherent reception of vector signaling codes and hinder decoding, as existing methods fail to accurately measure and correct for these timing variations.
Innovation Solution
The system employs multi-input comparators to generate composite skew measurement signals by forming linear combinations of received symbols, updating wire-specific skew values, and using adjustable delay elements to compensate for skew, ensuring accurate sampling and decoding of vector signaling codes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If existing skew measurement methods are used, then measurement simplicity is maintained, but measurement precision deteriorates due to inability to accurately measure timing variations across multiple wires
Solution Approach 1:
The patent segments the skew measurement process into multiple independent components: individual wire delay measurements, composite skew calculation, and iterative correction. Each wire's skew is measured and corrected separately through multiple iterations, allowing precise measurement without requiring a completely complex unified measurement system.
Solution Approach 2:
The patent introduces an intermediary computational process that combines individual wire delay measurements into composite skew measurements. This intermediary step uses linear combinations of received symbols to derive skew values, acting as a mediator between raw measurements and final correction values, thereby improving precision without directly increasing hardware complexity.
2Reliability
If skew correction is not applied, then device complexity is minimized, but reliability deteriorates due to inability to decode vector signaling codes accurately
Solution Approach 1:
The patent implements a feedback mechanism where skew measurements are continuously taken, processed to determine correction values, applied to the wire delays, and then re-measured to verify improvement. This closed-loop feedback system ensures reliable decoding by iteratively reducing skew until it falls within acceptable thresholds for accurate vector signaling code detection.
Solution Approach 2:
The patent performs preliminary skew measurements and corrections during a training phase before actual data transmission begins. By measuring and correcting skew in advance using known test patterns, the system ensures that the communication channel is properly calibrated for reliable decoding of subsequent data without requiring complex real-time correction during active communication.
3Measurement precision
If sampling times are not aligned with eye plot center, then device complexity is reduced, but measurement precision deteriorates due to reduced timing window for proper reception
Solution Approach 1:
The patent employs dynamic timing adjustment where sampling times are continuously optimized based on measured skew values. The system dynamically shifts sampling instants to align with the center of the eye plot by adjusting wire delays according to measured skew, allowing the timing to adapt to channel conditions rather than using fixed sampling times.
Solution Approach 2:
The patent changes the timing parameter of sampling operations based on measured skew conditions. By adjusting the sampling time offset for each wire according to its measured delay characteristics, the system optimizes the sampling instant to capture signals at the optimal point in the eye diagram, thereby improving measurement precision without requiring fundamentally complex timing alignment hardware.
Data Source
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AI summary
Methods and systems are described for receiving, over a plurality of consecutive signaling intervals, a plurality of codewords, each codeword received as a plurality of symbols via wires of a multi-wire bus, the plurality of symbols received at a plurality of multi-input comparators (MICs), wherein each symbol is received by at least two MICs, generating, for each codeword, a corresponding linear combination of the received symbols, generating a plurality of composite skew measurement signals over the plurality of consecutive signaling intervals, each composite skew measurement signal based on samples of one or more linear combinations, and updating wire-specific skew values of the wires of the multi-wire bus, wherein one or more wire-specific skew values are updated according to composite skew measurement signals associated with linear combinations formed by at least two different MICs.