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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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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: 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

Permittivity: 8.8 (Al)Conductor:Au

Use Terminals in HFSS to assign

Differential Pairs!!

Four coupled differential Lines connected

with flair on both edges

• 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