Coupled Differential Pair Crosstalk Study - PowerPoint PPT Presentation

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Coupled Differential Pair Crosstalk Study

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  1. Coupled Differential Pair Crosstalk Study Joon Hyung Chung

  2. 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

  3. What is Differential pair Transmission Line? 1 2 Figure 1:A symmetric Pair • Any multiples of two coupled transmission lines including the • Return path

  4. Differential Pair Even/Odd Analysis 1 2

  5. Growing Importance of Differential Pair High speed interconnect (LVDS) Rambus RDRAMs clocks Gigabit Ethernet IEEE 1394(High Speed Serial Bus)

  6. 8 Port Differential Pair Lines Fan-Out Fan-Out 1 5 Differential Pairs 2 6 8 4 7 3

  7. Measurement Probe Station, Network Analyzer Problem Tight Coupling (Need for Fan-Out) De-embedding Difficult to simulate Solutions ???

  8. 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

  9. 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

  10. Differential Pairs

  11. Differential Pairs

  12. 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

  13. Approach I Use ABCD parameters of the individual network Single-ended Measurement of Fan-Out in three standards (Short, Open, Load) Matrix manipulation

  14. 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

  15. 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