Differential to Common Mode Conversion Due to Asymmetric Ground Via Configurations

Transcription

1 Differential to Common Mode Conversion Due to Asymmetric Ground Via Configurations Renato Rimolo-Donadio Xiaomin Duan, Heinz-Dietrich Brüns, Christian Schuster Institut für Technische Universität Hamburg-Harburg, Germany Workshop on Signal Propagation on Interconnects May 14, 2009 Technische Universität Hamburg-Harburg

2 Motivation Asymmetries on passive interconnects channels lead to Differential Model to Common Mode (DM/CM) Conversion How important can asymmetric via configurations be for the DM/CM conversion? How to mitigate DM/CM mode conversion effects Via Array Signal Via Ground Via Differential Trace Via Array 2

3 Contents Modeling Approach Study Case Mode Conversion Due to Asymmetric Ground Via Configurations Mode Conversion Due to Trace Length Mismatch Combined Effect of Asymmetric Ground Vias and Trace Length Mismatch Mitigation of Mode Conversion Conclusions 3

4 Contents Modeling Approach Study Case Mode Conversion Due to Asymmetric Ground Via Configurations Mode Conversion Due to Trace Length Mismatch Combined Effect of Asymmetric Ground Vias and Trace Length Mismatch Mitigation of Mode Conversion Conclusions 4

5 Modeling Approach Port 1 Port 2 Port 1 Port 2 C v C v Modal Transformation Parallel-Plane Impedance (Zpp) pp ) Transmission Parallel-Plane Line Impedance (Z tl ) (Zpp) Modal Transformation C v C v PCB Cross-Section Method primarily based on analytical formulations [1-6] Cv: Via-Plane Capacitances 5

6 Modeling Approach Port 1 Port 2 Port 1 Port 2 Cavity 1 Cavity n Very good numerical efficiency allows fast simulations (seconds) 6

7 Modeling Approach Port 1 Port 2 Port 1 Port 2 Cavity 1 S Parameter Block (mixed-mode) S dd S dc S cd S cc Cavity n Very good numerical efficiency allows fast simulations (seconds) 7

8 Contents Modeling Approach Study Case Mode Conversion Due to Asymmetric Ground Via Configurations Mode Conversion Due to Trace Length Mismatch Combined Effect of Asymmetric Ground Vias and Trace Length Mismatch Mitigation of Mode Conversion Conclusions 8

9 Study Case Transmission along the link for a trace routed at different layers 9

10 Contents Modeling Approach Study Case Mode Conversion Due to Asymmetric Ground Via Configurations Mode Conversion Due to Trace Length Mismatch Combined Effect of Asymmetric Ground Vias and Trace Length Mismatch Mitigation of Mode Conversion Conclusions 10

11 Asymmetric Ground Via Configuration Model FEM Sim. (HFSS) DM/CM conversion increases as the asymmetry is placed closer to the via pair 11

12 Asymmetric Ground Via Configuration Model FEM Sim. (HFSS) Asymmetries located at a distance larger than twice the via pitch have small impact (mode conversion below -30dB) 12

13 Asymmetric Via Configuration Side 1 Side 2 DM/CM conversion for different asymmetric ground via configurations Asymmetric Ground Via Configuration 1 GND on side 2 S 5 GHz (db) S 5 GHz (db) GND on side 1 / 1 GND on side GND on side 1 / 2 GND on side GND on side 1 / 3 GND on side The distance to the nearest signal via d was 40 mils, trace routed in layer S12. 13

14 Contents Modeling Approach Study Case Mode Conversion Due to Asymmetric Ground Via Configurations Mode Conversion Due to Trace Length Mismatch Combined Effect of Asymmetric Ground Vias and Trace Length Mismatch Mitigation of Mode Conversion Conclusions 14

15 Trace Length Mismatch A trace length difference introduces an amount of mode conversion comparable to the one introduced by an asymmetric ground via configuration (-20 to -40 db) 15

16 Contents Modeling Approach Study Case Mode Conversion Due to Asymmetric Ground Via Configurations Mode Conversion Due to Trace Length Mismatch Combined Effect of Asymmetric Ground Vias and Trace Length Mismatch Mitigation of Mode Conversion Conclusions 16

17 Combined Effect Case B shows less DM/CM conversion with respect to case A below 25 GHz 17

18 Contents Modeling Approach Study Case Mode Conversion Due to Asymmetric Ground Via Configurations Mode Conversion Due to Trace Length Mismatch Combined Effect of Asymmetric Ground Vias and Trace Length Mismatch Mitigation of Mode Conversion Conclusions 18

19 Effect of Ground Via Propagation velocity tends to increase as the distance to the ground via decreases (via tends to appear electrically shorter). 19

20 Combined Effect Upper side vias tend to appear electrically longer due to ground via configuration Trace length difference Trace length difference Upper side vias tend to appear electrically longer due to ground via configuration Both effects will increase the imbalance between the two link paths Effect of the asymmetric ground via configuration tends to compensate trace length mismatch 20

21 Conclusions Physics-based via and trace models have been applied to simulate efficiently the DM/CM conversion in differential links. Both asymmetric ground via configurations and trace length mismatch can lead to a considerable amount of mode conversion The nearest neighbors are the vias of more concern for the DM/CM conversion If asymmetries cannot be avoided when designing a link, the mode conversion due to trace length mismatch can be mitigated by asymmetric ground via configurations and vice versa. 21

22 References [1] G. Selli, C. Schuster, Y. Kwark, M. Ritter, J. L. Drewniak, Model-to-Hardware Correlation of Physics-Based Via Models With the Parallel Plate Impedance Included, in Proc. IEEE Symposium on Electromagnetic Compatibility, Portland, USA, Aug [2] C. Schuster, G. Selli, Y. H. Kwark, M. B. Ritter, J. L. Drewniak, Progress in Representation and Validation of Physics-Based Via Models, in Proc 11th IEEE Workshop on Signal Propagation on Interconnects, May 13-16, Genova, Italy, [3] R. Rimolo-Donadio, A. J. Stepan, H.-D. Brüns, J. L. Drewniak, and C. Schuster, Simulation of via interconnects using physics-based models and microwave network parameters, in Proc. 12th IEEE Workshop Signal Propagation on Interconnects, Avignon, France, May [4] R. Rimolo-Donadio, H.-D. Brüns, C. Schuster, Including stripline connections into network parameter based via models for fast simulation of interconnects, in Proc. 20th Int. Zurich Symposium on Electromagnetic Compatibility, Switzerland, Jan [5] A. E. Engin, W. John, G. Sommer, W. Mathis, and H. Reichl, Modeling of striplines between a power and a ground plane, IEEE Trans. Adv. Pack., vol. 29, no. 3, pp , Aug [6] X. Gu, F. De Paulis, R. Rimolo-Donadio, K. Shringarpure, Y. Zhang, B.. Archambeault, S. Connor, Y. H. Kwark, M. B. Ritter, J. Fan, C. Schuster, Fully analytical methodology for fast end-to-end link analysis on complex printed circuit boards including signal and power integrity effects, IEC DesignCon 09, Santa Clara, CA, USA, Feb [7] J. C. Parker, Jr., Via Coupling within Parallel Rectangular Planes, IEEE Trans. Electromagn. Compat., vol. 39, no. 1, pp , Feb [8 ] Y. Zhang, J. Fan, G. Selli, M. Cocchini, and F. De Paulis, Analytical Evaluation of Via-Plate Capacitance for Multilayer Printed Circuit Boards and Packages, IEEE Trans. Microwave Theory Techn., vol. 56, no. 9, pp , Sep [9] HFSSTM, Ver. 11, Ansoft Corporation, Pittsburgh, USA,