Slew Rate Control Circuit for Open-Drain I2C Signal Integrity

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Solution Overview

Problem

The high slew rate of the I2C signal in an open-drain configuration interferes with adjacent signals, leading to potential test failures and interference issues, particularly in HDMI and eARC connections, and existing solutions like series resistors or grounding capacitors can cause compliance test failures or increase material costs.

Innovation Solution

A slew rate control circuit using switches and switching circuits with resistances to control the slew rate without additional elements, comprising a first and second switch connected between a power wire and an output end, and first and second switching circuits with resistances to drive these switches, along with grounding capacitors connected to their control ends, allowing inverse driving for slew rate adjustment.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Object-affected harmful factors

If a series resistor is added to reduce the slew rate of the I2C signal, then the interference with adjacent signals is reduced, but the low level potential of the signal is affected and may cause compliance test failure

Engineering Contradiction:

Improveinterference with adjacent signalsVSAvoidcompliance test specification

Core Design Contradiction:

Object-affected harmful factorsVSReliability

Solution Approach 1:

The patent introduces a dedicated slew rate control circuit as an intermediary component between the I2C signal source and the output. This circuit uses switching elements and capacitors to actively manage the signal transition, reducing the harmful high slew rate effect on adjacent signals while maintaining signal integrity and compliance with test specifications.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The patent dynamically changes the electrical parameters (slew rate) of the I2C signal through controlled switching actions. By using switches and capacitors to temporarily alter the signal characteristics during transitions, the circuit reduces the slew rate only when necessary, preserving both signal quality and compliance without permanently affecting signal levels.

Inventive Principle:

Principle #35Parameter changes

2Object-affected harmful factors

If a grounding capacitor is added to reduce the slew rate of the I2C signal, then the interference with adjacent signals is reduced, but the capacitive reactance increases and may cause compliance test failure

Engineering Contradiction:

Improveinterference with adjacent signalsVSAvoidcompliance test specification

Core Design Contradiction:

Object-affected harmful factorsVSReliability

Solution Approach 1:

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

Inventive Principle:

Principle #35Parameter changes

3Object-affected harmful factors

If ferrite beads are connected in series to decrease the slew rate of the I2C signal, then the interference with adjacent signals is reduced, but the material cost increases

Engineering Contradiction:

Improveinterference with adjacent signalsVSAvoidmaterial cost

Core Design Contradiction:

Object-affected harmful factorsVSEase of manufacture

Solution Approach 1:

The patent extracts the slew rate control function from external passive components (like ferrite beads) and implements it using active switching elements and capacitors that are already part of the circuit architecture. This eliminates the need for additional expensive materials while achieving the same interference reduction effect.

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

Inventive Principle:

Principle #35Parameter changes

4Ease of operation

If the open-drain configuration is used to implement the I2C signal, then the high level is achieved by external pull-up circuit, but the slew rate of pulling down the signal becomes very high causing interference

Engineering Contradiction:

Improveopen-drain configurationVSAvoidinterference with adjacent signals

Core Design Contradiction:

Ease of operationVSObject-affected harmful factors

Solution Approach 1:

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

Inventive Principle:

Principle #35Parameter changes

Data Source

PatentUS20260066884A1Connector circuit, control circuit, and slew rate control circuit thereof

Publication Date: 2026.03.05 REALTEK SEMICON CORP

AI summary

A slew rate control circuit includes a ground wire, a power wire, an output end, two switches, two switching circuits, and two grounding capacitors. The switches are respectively connected between the power wire and the output end and between the output end and the ground wire. The switching circuits are respectively connected between the power wire and the ground wire and controlled by two driving signals and thus inversely driven. One of the switching circuits is configured to drive one of the switches through the first resistance, and the other is configured to drive the other one of the switches through the second resistance. One of the grounding capacitors is connected to a control end of the first switch and one of the switching circuits, and the other is connected to a control end of the second switch and the other one of the switching circuits.