Linear Feedback Equalizer for ISI Reduction Without Noise Amplification

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Solution Overview

Problem

Existing digital communication systems face challenges in reducing or eliminating intersymbol interference (ISI) and noise amplification, particularly in high-frequency components, due to limitations in feed forward and decision feedback equalization techniques.

Innovation Solution

The implementation of a linear feedback equalization system that includes comparators to digitize analog signals, digital-to-analog converters to create feedback analog signals, and a subtractor to subtract these signals from the output of a continuous-time linear equalizer, providing the difference as incoming analog signals to reduce or eliminate ISI.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If feed forward equalization is used to reduce ISI, then signal quality is improved, but noise amplification occurs particularly in high-frequency components

Engineering Contradiction:

Improvesignal qualityVSAvoidnoise amplification

Core Design Contradiction:

ReliabilityVSObject-generated harmful factors

Solution Approach 1:

The patent implements feedback equalization where the equalizer uses feedback from previously detected symbols to compensate for ISI. The equalizer coefficient is calculated based on the difference between the detected symbol and the transmitted symbol, and this coefficient is applied to feedback signals to reduce ISI in subsequent symbols, thereby improving signal quality without amplifying noise as feed forward equalization does

Inventive Principle:

Principle #23Feedback

Solution Approach 2:

The equalizer performs self-adjustment by automatically calculating its own coefficients based on detection errors. The system uses the detected symbols and transmitted symbols to compute the equalizer coefficient, enabling the system to self-correct and improve signal quality without external intervention while avoiding noise amplification

Inventive Principle:

Principle #25Self-service

2Reliability

If decision feedback equalization is used to reduce ISI, then signal quality is improved, but aggressive decision timing is required

Engineering Contradiction:

Improvesignal qualityVSAvoiddecision timing

Core Design Contradiction:

ReliabilityVSLoss of time

Solution Approach 1:

The patent uses a simplified feedback mechanism that only requires one previously detected symbol for feedback, rather than multiple symbols. This partial action approach reduces the timing constraints and decision complexity while still achieving ISI reduction and improving signal quality

Inventive Principle:

Principle #16Partial or excessive action

Solution Approach 2:

The equalization process is segmented into distinct stages: analog-to-digital conversion, equalization with feedback subtraction, and decision making. This segmentation allows the feedback operation to occur in the digital domain after conversion, relaxing the timing requirements compared to analog decision feedback equalization

Inventive Principle:

Principle #1Segmentation

3Reliability

If complex equalization techniques are used to eliminate ISI, then signal quality is improved, but system complexity increases

Engineering Contradiction:

Improvesignal qualityVSAvoidsystem complexity

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The patent changes the domain of operation from analog to digital for the feedback equalization process. By performing the feedback subtraction in the digital domain after analog-to-digital conversion, the system achieves ISI elimination with simpler digital circuitry rather than complex analog equalization circuits

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent replaces complex analog equalization mechanics with digital signal processing. The feedback equalization is implemented using digital-to-analog converters and digital subtraction operations, which are simpler and more reliable than analog equalization circuits while achieving the same ISI elimination effect

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

4Reliability

If complex equalization techniques are used to eliminate ISI, then signal quality is improved, but power consumption increases

Engineering Contradiction:

Improvesignal qualityVSAvoidpower consumption

Core Design Contradiction:

ReliabilityVSUse of energy by moving object

Solution Approach 1:

The patent replaces power-intensive analog equalization circuits with lower-power digital signal processing operations. The feedback equalization is performed using digital-to-analog converters and digital subtraction, which consume less power than complex analog equalization circuits while achieving effective ISI elimination and maintaining signal quality

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Data Source

PatentUS10411917B2Linear feedback equalization

Publication Date: 2019.09.10 CREDO TECHNOLOGY GROUP LTD

AI summary

A linear feedback equalizer includes comparators that digitize incoming analog signals. The equalizer further includes digital-to-analog converters (“DACs”) that transform a current digitized signal into one or more feedback analog signals. The equalizer further includes a subtractor that subtracts the feedback analog signals from the output of a continuous-time linear equalizer (“CTLE”) and provides the difference to the comparators as incoming analog signals.