Coupled Differential Pair Crosstalk Study

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# Coupled Differential Pair Crosstalk Study - PowerPoint PPT Presentation

Coupled Differential Pair Crosstalk Study. Joon Hyung Chung. Overview . Introduction to Differential Pair - What is Differentail Pair Transmission Line? - Differential Pair Even/Odd Mode Analysis - Growing Importance of Differential Pair Schematics Measurement

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## Coupled Differential Pair Crosstalk Study

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Presentation Transcript

Joon Hyung Chung

### Overview

• Introduction to Differential Pair
• - What is Differentail Pair Transmission Line?
• - Differential Pair Even/Odd Mode Analysis
• - Growing Importance of Differential Pair
• Schematics
• Measurement
• Issues/Challenge
• Design

### What is Differential pair Transmission Line?

1

2

Figure 1:A symmetric Pair

• Any multiples of two coupled transmission lines including the
• Return path

1

2

### Growing Importance of Differential Pair

High speed interconnect (LVDS)

Rambus RDRAMs clocks

Gigabit Ethernet

IEEE 1394(High Speed Serial Bus)

### 8 Port Differential Pair Lines

Fan-Out

Fan-Out

1

5

Differential Pairs

2

6

8

4

7

3

### Measurement

Probe Station, Network Analyzer

Problem

Tight Coupling (Need for Fan-Out)

De-embedding

Difficult to simulate

Solutions ???

Objective and Challenges

Objective: To accurately provide the x-talk

of the differential pair and correlate the measured values

with the simulated result

• Challenges
• 1. Simulation aspect:
• To separate even and odd mode without
• perturbations from each other
• 2. Measurement aspect:
• To be able to separate the fan-out and de-embedded
• model to measure the S & ABCD parameter matrices
• correctly

Differential Pairs

Permittivity: 8.8 (Al)Conductor:Au

Use Terminals in HFSS to assign

Differential Pairs!!

Four coupled differential Lines connected

with flair on both edges

Differential Pairs

• Result in HFSS indicates that common mode
• exist in the differential mode of the S matrix
• Unwanted modes add up(crosstalk) due to asymmetry of the differential system

### Approach I

Use ABCD parameters of the individual network

Single-ended Measurement of Fan-Out in three standards (Short, Open, Load)

Matrix manipulation

### Approach I (Continued)

Fan-Out 2

[ABCD]1

Fan-Out1

[ABCD]2

[ABCD]3

• How do we get ABCD matrix from measurement?
• Measure S parameters of Fan-Out1
• S matrix is converted into Z matrix
• Z matrix is converted into ABCD matrix
• Measure Overall S parameters of the whole system
• Use symmetry to get individual S parameters of Fan-out 2

### Approach (Continued)

De-embed the differential pair

Use even and odd analysis to find differential S parameters to find the crosstalk

Code in Mat-Lab to verify the theory

Measurement of S parameter needed