Rterm Modulation for Pad Capacitance in High-Speed Serial I/O

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Solution Overview

Problem

Pad capacitance (Cpad) limits high-speed serial I/O performance by reducing rise/fall edge rate, causing insertion loss, termination mismatch, and Inter-Symbol Interference (ISI) jitter, which affects signal processing and synchronization in serial communication systems.

Innovation Solution

The Rterm modulation system dynamically adjusts termination resistance in current mode drivers to quickly charge or discharge pad capacitance during transitions, enhancing signal edge sharpness and eye margin by increasing resistance during rising transitions and decreasing it during falling transitions, thereby mitigating Cpad effects.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Use of energy by moving object

If pad capacitance is present in high-speed serial I/O, then the circuit can store charge during transitions, but the rise/fall edge rate is reduced and signal quality deteriorates

Engineering Contradiction:

Improvecharge storage capabilityVSAvoidrise/fall edge rate

Core Design Contradiction:

Use of energy by moving objectVSSpeed

Solution Approach 1:

The patent applies dynamics by making the termination resistance variable rather than fixed. The Rterm modulation system dynamically adjusts the termination resistance value based on the signal transition state (rising or falling edge), allowing the system to optimize charging and discharging speeds adaptively. This resolves the contradiction by enabling fast edge rates while still managing the charge storage function of the pad capacitance.

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The patent changes the parameter of termination resistance from a constant value to a modulated variable value. By varying the resistance parameter in response to signal transitions, the system can control the charging and discharging rates of the pad capacitance, thereby maintaining sharp signal edges while utilizing the capacitance for signal integrity management.

Inventive Principle:

Principle #35Parameter changes

2Stability of the object's composition

If pad capacitance is present, then charge can be maintained during transitions, but insertion loss and termination mismatch increase

Engineering Contradiction:

Improvecharge maintenance during transitionsVSAvoidinsertion loss

Core Design Contradiction:

Stability of the object's compositionVSLoss of energy

Solution Approach 1:

The patent employs feedback through the Rterm modulation system that responds to signal transition states. The termination resistance is adjusted based on feedback from the detected transition condition (rising or falling edge), allowing the system to optimize impedance matching dynamically. This reduces reflection and insertion loss while maintaining charge stability during transitions.

Inventive Principle:

Principle #23Feedback

3Duration of action of moving object

If pad capacitance is present, then signal can be buffered, but Inter-Symbol Interference (ISI) jitter is produced

Engineering Contradiction:

Improvesignal buffering durationVSAvoidsignal synchronization accuracy

Core Design Contradiction:

Duration of action of moving objectVSReliability

Solution Approach 1:

The patent applies periodic action through the modulation of termination resistance that occurs with each signal transition. The Rterm is periodically adjusted in sync with the data transitions, creating a rhythmic charging/discharging pattern that prevents charge accumulation and reduces ISI jitter. This periodic modulation maintains signal buffering while preserving synchronization accuracy.

Inventive Principle:

Principle #19Periodic action

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 approach improves high-speed serial I/O performance by increasing eye margin, reducing signal loss, and minimizing ISI jitter, leading to sharper signal transitions and better synchronization in communication channels.

Implementation Method 1

a pad coupled to the switch and having a pad capacitance that charges and discharges based on changes between the first and second states

Methodology Applied

Scientific EffectCapacitance charging and discharging: Capacitance

Implementation Method 2

a resistor coupled to the switch and the pad, the resistor configured to be modulated to reduce a charging or discharging time of the pad capacitance

Methodology Applied

Scientific EffectElectrical resistance modulation: Electrical Resistance

Data Source

PatentUS9306555B2Apparatus and method to achieve CPAD mitigation effects

Publication Date: 2016.04.05 INTEL CORP

AI summary

An apparatus is configured to achieve Cpad mitigation effects. The apparatus may include a switch coupled to a current source with first and second states. The apparatus may also include a pad coupled to the switch and having a pad capacitance that charges and discharges based on changes between the first and second switch states. The apparatus may further include a resistor coupled to the switch and the pad, and the resistor is configured to be modulated to reduce the charging or discharging time of the pad.