LVDS Transceiver Impedance Control for Common-Mode Noise Filtering

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Solution Overview

Problem

Low-voltage differential signaling (LVDS) transmission systems face increased noise risks due to common-mode noise, which can cause voltage deviations outside acceptable ranges, and legacy transceivers with common-mode chokes introduce impedance issues and resonation peaks, complicating data interpretation.

Innovation Solution

The transceiver employs teeter-totter circuitry to maintain high impedance for differential-mode components and low impedance for common-mode components, allowing the use of common-mode chokes and capacitors that were not possible in legacy systems, thereby filtering common-mode noise while preserving differential-mode signals.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Object-affected harmful factors

If common-mode chokes are used to filter common-mode noise, then common-mode noise filtering is improved, but impedance issues and resonation peaks are introduced that complicate data interpretation

Engineering Contradiction:

Improvecommon-mode noiseVSAvoidimpedance control

Core Design Contradiction:

Object-affected harmful factorsVSDevice complexity

Solution Approach 1:

The patent segments the impedance control function by providing different impedance values for differential-mode signals versus common-mode signals. The teeter-totter circuitry creates a segmented impedance structure where differential-mode signals see high impedance while common-mode signals see low impedance, allowing the common-mode choke to filter noise without causing resonation peaks that would complicate data interpretation.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The patent applies local quality by making the impedance characteristic location-dependent and mode-dependent. The teeter-totter circuitry ensures that at the transceiver input, differential-mode signals encounter high impedance while common-mode signals encounter low impedance. This localized quality control allows the common-mode choke to effectively filter common-mode noise without introducing system-wide resonation peaks.

Inventive Principle:

Principle #3Local quality

2Use of energy by moving object

If voltage difference between lines is reduced to save energy, then energy consumption is reduced, but noise susceptibility increases

Engineering Contradiction:

Improveenergy consumptionVSAvoidnoise susceptibility

Core Design Contradiction:

Use of energy by moving objectVSObject-affected harmful factors

Solution Approach 1:

The patent changes the impedance parameter dynamically based on signal mode. By using teeter-totter circuitry to provide high impedance for differential-mode signals and low impedance for common-mode signals, the system maintains low voltage differential signaling (saving energy) while the high differential-mode impedance protects against noise susceptibility. This parameter change allows the system to operate in the low-voltage regime without sacrificing noise immunity.

Inventive Principle:

Principle #35Parameter changes

3Adaptability or versatility

If multiple transceivers are coupled to a single transmission line, then system integration is improved, but noise interference between transceivers increases

Engineering Contradiction:

Improvesystem integrationVSAvoidnoise interference

Core Design Contradiction:

Adaptability or versatilityVSObject-affected harmful factors

Solution Approach 1:

The patent converts the potential harm of multiple transceivers sharing a transmission line into a benefit by using the teeter-totter circuitry to create high differential-mode impedance. This high impedance isolates each transceiver's differential-mode signals from others on the same transmission line, preventing noise interference while maintaining system integration. The common-mode choke further benefits this isolation by filtering out any common-mode noise that might couple between transceivers.

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

Applied Scientific Principles

This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.

Function Achieved in This Case

This solution effectively filters common-mode noise, preventing voltage deviations and maintaining high differential-mode impedance, resulting in a more robust transceiver that can operate at higher frequencies with reduced noise interference.

Implementation Method 1

the common-mode choke circuitry to pass a differential-mode component of an input signal and filter a common-mode component of the input signal

Methodology Applied

Scientific EffectElectrical Impedance: Electrical Resistance

Implementation Method 2

the teeter-totter circuitry to provide high impedance for the differential-mode component of the input signal and low impedance for the common-mode component of the input signal

Methodology Applied

Scientific EffectElectrical Impedance: Electrical Resistance

Data Source

PatentUS11728778B2Differential signaling transmission systems

Publication Date: 2023.08.15 ANALOG DEVICES INT UNLTD CO

AI summary

A transceiver that may be implemented in low-voltage differential signaling (LVDS) transmission system or a multipoint LVDS transmission system, and corresponding systems are disclosed herein. The transceiver can filter a common-mode component of a differential input signal input into the transceiver while maintaining a high impedance for a differential-mode component of the differential input signal. The transceiver utilizes teeter-totter circuitry to maintain the high impedance for the differential-mode component of the differential input signal.