Coupled differential pair crosstalk study
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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

Overview l.jpg

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 l.jpg

What is Differential pair Transmission Line?

1

2

Figure 1:A symmetric Pair

  • Any multiples of two coupled transmission lines including the

  • Return path



Growing importance of differential pair l.jpg

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 l.jpg

8 Port Differential Pair Lines

Fan-Out

Fan-Out

1

5

Differential Pairs

2

6

8

4

7

3


Measurement l.jpg

Measurement

Probe Station, Network Analyzer

Problem

Tight Coupling (Need for Fan-Out)

De-embedding

Difficult to simulate

Solutions ???


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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


Slide9 l.jpg

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




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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 l.jpg

Approach I

Use ABCD parameters of the individual network

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

Matrix manipulation


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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 l.jpg

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


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