PAM4 Encoding That Preserves 8b10b NRZ Spectral Density

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Solution Overview

Problem

Existing PAM4 modulations disrupt the power spectral density (PSD) of 8b10b NRZ, compromising transmission throughput and compatibility.

Innovation Solution

Employing a system with first and second 8b10b encoders to split the original byte stream and perform a linear combination, converting pairs of bits into PAM4 symbols that preserve the 8b10b NRZ PSD, enabling band separation between downlink and uplink channels.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Productivity

If standard PAM4 modulation is used, then transmission throughput is improved, but power spectral density compatibility with 8b10b NRZ is lost

Engineering Contradiction:

Improvetransmission throughputVSAvoidPSD compatibility

Core Design Contradiction:

ProductivityVSAdaptability or versatility

Solution Approach 1:

The patent changes the modulation parameter from standard PAM4 to a modified PAM4 scheme where symbols are carefully selected to preserve the power spectral density characteristics of 8b10b NRZ. This allows maintaining compatibility with existing 8b10b NRZ systems while achieving PAM4 throughput

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent segments the PAM4 symbol selection into two independent 8b10b encoded bit streams. By treating the in-phase and quadrature components separately and encoding them independently with 8b10b, the system preserves the spectral properties of each component while combining them to achieve PAM4 modulation

Inventive Principle:

Principle #1Segmentation

2Adaptability or versatility

If 8b10b encoding is applied to both bit streams, then PSD preservation is improved, but device complexity increases

Engineering Contradiction:

ImprovePSD preservationVSAvoidencoding complexity

Core Design Contradiction:

Adaptability or versatilityVSDevice complexity

Solution Approach 1:

The patent uses two identical 8b10b encoders that can be independently configured to encode separate bit streams. This universal approach allows the same encoding logic to be applied to both in-phase and quadrature components, simplifying implementation while preserving PSD characteristics

Inventive Principle:

Principle #6Universality (Multi-functionality)

3Ease of operation

If band separation is implemented, then echo cancellation requirements are reduced, but transmission system complexity increases

Engineering Contradiction:

Improveecho cancellation requirementVSAvoidtransmission system complexity

Core Design Contradiction:

Ease of operationVSDevice complexity

Solution Approach 1:

The patent introduces a quadrature dimension to the transmission system by modulating both in-phase and quadrature bit streams. This dimensional expansion creates natural band separation between uplink and downlink channels, reducing echo cancellation requirements without significantly increasing overall system complexity

Inventive Principle:

Principle #17Another dimension (Dimensionality change)

Data Source

PatentEP3997845B18b10b PAM4 encoding

Publication Date: 2025.11.19 VALENS SEMICON

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AI summary

Encoding PAM4 or PAMS symbols to have a power spectral density (PSD) similar to the PSD of a standard 8b 10b Non-Return-to-Zero stream. In one embodiment, a transmitter includes first and second 8b 10b encoders that receive first and second streams split from an original byte stream. The first and second 8b 10b encoders output first and second 8b 10b streams, respectively. The first and second 8b 10b streams are fed into a 2 -bit combiner that performs a linear combination of the first and second 8b 10b 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 8b 10b non-return-to-zero stream.