PAM-3 Encoder and Decoder for DRAM Bandwidth With Wider Eye Margins
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Solution Overview
Problem
Current DRAM technologies face limitations in scaling bandwidth due to eye-closure issues and noise susceptibility in high-speed signaling, particularly with PAM-4 signaling, which increases complexity and costs, while PAM-3 offers potential benefits but requires more pins for data encoding.
Innovation Solution
Implementing PAM-3 signaling with 11b7s and 3b2s encoding techniques to efficiently encode data on a 12-pin interface, utilizing CRC, poison, and severity bits to achieve comparable throughput to PAM-4 with reduced circuit complexity and increased eye margins.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If PAM-4 signaling is used to increase DRAM bandwidth, then throughput is improved, but eye-closure increases and noise susceptibility worsens
Solution Approach 1:
The patent changes the signaling parameter from PAM-4 (4 voltage levels) to PAM-3 (3 voltage levels), which increases the voltage margin between levels and reduces eye-closure. This parameter change maintains high bandwidth by using efficient encoding schemes (11b7s and 3b2s) that achieve comparable throughput to PAM-4 while improving signal reliability and noise immunity.
2Productivity
If PAM-4 signaling is used to increase interface rate, then throughput is improved, but circuit complexity increases
Solution Approach 1:
The patent segments the data encoding into two distinct modes: 11b7s encoding for high-throughput scenarios and 3b2s encoding for lower-throughput scenarios. This segmentation allows the system to optimize circuit complexity by selecting the appropriate encoding mode based on bandwidth requirements, avoiding the need for overly complex PAM-4 encoding circuits while maintaining flexibility in throughput optimization.
3Device complexity
If PAM-3 signaling is used to reduce complexity, then circuit area is reduced, but more pins are required for data encoding
Solution Approach 1:
The patent implements a universal 12-pin interface that can operate in multiple modes (PAM-3 with 11b7s encoding, PAM-3 with 3b2s encoding, and potentially PAM-4). This multi-functionality allows the same physical pins to accommodate different encoding schemes and bandwidth requirements, eliminating the need for additional pins while maintaining circuit simplicity through standardized PAM-3 signaling.
4Use of energy by moving object
If voltage scaling is applied to PAM-4 operation, then power consumption is reduced, but noise susceptibility increases
Solution Approach 1:
The patent changes the voltage parameter from PAM-4 operation to PAM-3 operation, which inherently provides larger voltage margins between signal levels. This parameter change enables voltage scaling for reduced power consumption while simultaneously improving noise immunity, as the larger voltage steps in PAM-3 are more resistant to noise interference even at lower voltage levels.
Data Source
AI summary
Data bits are encoded in one or both of an eleven bit seven pulse amplitude modulated three-level (PAM-3) symbol (11b7s) format and a three bit two symbol (3b2s) format on a plurality of data channels, one or more auxiliary data channels, and an error correction channel. One or more of a cyclic redundancy check (CRC) value, a poison value, and a severity value are encoded as 11b7s and/or 3b2s PAM-3 symbols on an error correction channel.