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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

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

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

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

8 Port Differential Pair Lines

Fan-Out

Fan-Out

1

5

Differential Pairs

2

6

8

4

7

3

measurement

Measurement

Probe Station, Network Analyzer

Problem

Tight Coupling (Need for Fan-Out)

De-embedding

Difficult to simulate

Solutions ???

slide8
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
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

slide12
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

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

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

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

ad