8b10b-Based PAM4 Encoding for PSD-Compatible High-Speed Links

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Solution Overview

Problem

Standard 4-level pulse-amplitude modulation (PAM4) technologies do not preserve the power spectral density (PSD) of 8b10b Non-Return-to-Zero (NRZ) line code, which is essential for maintaining transmission throughput and compatibility with 8b10b characteristics.

Innovation Solution

Combining two 8b10b encoders to form a PAM4 modulation with a PSD similar to standard 8b10b NRZ, using a 2-bit or 3-bit combiner to linearly combine bit streams and convert them into PAM4 or PAM8 symbols, respectively, while maintaining the original byte stream's characteristics.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Productivity

If standard PAM4 modulation is used to improve transmission throughput, then data rate increases, but power spectral density compatibility with 8b10b NRZ is lost

Engineering Contradiction:

Improvetransmission throughputVSAvoidPSD compatibility

Core Design Contradiction:

ProductivityVSReliability

Solution Approach 1:

The patent combines two 8b10b NRZ encoded bit streams using a 2-bit combiner to generate PAM4 symbols. This merging approach allows the system to achieve higher throughput via PAM4 while preserving the PSD characteristics of the underlying 8b10b encoding by maintaining the relationship between the combined streams.

Inventive Principle:

Principle #5Merging (Combining)

Solution Approach 2:

The patent changes the modulation parameter from standard PAM4 to a modified PAM4 scheme where the constellation points and symbol generation are derived from linear combinations of 8b10b encoded streams. This parameter change ensures the PSD maintains compatibility with standard 8b10b NRZ while enabling PAM4 throughput.

Inventive Principle:

Principle #35Parameter changes

2Device complexity

If band separation is implemented without echo cancellation to simplify receiver design, then device complexity decreases, but frequency interference between uplink and downlink increases

Engineering Contradiction:

Improvereceiver complexityVSAvoidfrequency interference

Core Design Contradiction:

Device complexityVSObject-affected harmful factors

Solution Approach 1:

The patent changes the spectral parameter of the transmitted signal by using PAM4 modulation derived from 8b10b encoding, which creates a specific PSD profile. This parameter change enables natural band separation between uplink and downlink channels, reducing frequency interference without requiring complex echo cancellation circuitry.

Inventive Principle:

Principle #35Parameter changes

Data Source

PatentUS11038726B28b10b PAM4 encoding

Publication Date: 2021.06.15 VALENS SEMICON

AI summary

Encoding PAM4 or PAM8 symbols to have a power spectral density (PSD) similar to the PSD of a standard 8b10b Non-Return-to-Zero stream. In one embodiment, a transmitter includes first and second 8b10b encoders that receive first and second streams split from an original byte stream. The first and second 8b10b encoders output first and second 8b10b streams, respectively. The first and second 8b10b streams are fed into a 2-bit combiner that performs a linear combination of the first and second 8b10b streams. And a 4-level Pulse Amplitude Modulation encoder (PAM4 encoder) converts the linear combination of each two bits, received from the combiner, into a PAM4 symbol. Wherein the resulting stream of PAM4 symbols has PSD similar to the PSD of the standard 8b10b non-return-to-zero stream.