Coupling and Cross-talk Analysis in High Speed Interconnects Md Amimul Ehsan Electrical Engineering and Computer Science Department, University of Kansas December 01, 2015

Outlines Motivation Introduction Signal/Ground Via Near and Far end crosstalk Optimized and non-optimized S/G Via Conclusion

Motivation Due to technology miniaturization, crosstalk is becoming increasingly becoming major concern in high speed designs. Higher integration density, causes electromagnetic radiation in device space. Merging process technology, mixed materials, system integration. Coupling noise between the vias is a significant design consideration.

Objectives Study on coupling and crosstalk which is critical for signal integrity. Investigation of via physical dimensions on induced crosstalk. Near end crosstalk (NEXT) and Far end crosstalk (EFXT) are analyzed for single ended and differential signal via.

Fig. 1: Examples of crosstalk; two conductors sharing same ground [1] Introduction Electromagnetic interference that disturbs neighbor is the crosstalk noise. The time changing electric and magnetic field in signal conductor induce energy to propagate along victim conductor. Fig. 1: Examples of crosstalk; two conductors sharing same ground [1] 2D

Impacts of Via Dimensions Placement of signal and ground via. Via radius. Via pitch Oxide insulator thickness (For TSV in 3D IC)

Signal/Ground Via Pattern Fig. 2. Via arrangement 4 single ended signals with 12 grounds Fig. 3. Via arrangement 4 single ended signals with 12 grounds (HFSS)

Single Ended Via Crosstalk Fig. 4. Near End Crosstalk of single ended signal Via with different pitch Fig. 5. Far End Crosstalk of single ended signal Via with different pitch

Differential Via Crosstalk Fig. 6. Near End Crosstalk of single ended and differential Via Fig. 7. Far End Crosstalk of single ended and differential Via

Optimized Differential S/G Via Fig. 8. Differential signal assignment of non- optimized TSV Fig. 9. Differential signal assignment of optimized TSV

Crosstalk Comparison V_NEXT (Volts) V_NEXT (Volts) Time (µs) Time (µs) Time = 39.06 nsec V_NEXT = 0.003 Max m1 Time = 5.115 nsec V_NEXT = - 0.001 Min V_NEXT (Volts) Time (µs) m2 Time = 7.015 nsec V_NEXT = 0.002 Max m1 Time = 86.17 nsec V_NEXT = - 0.000 Min Time (µs) V_NEXT (Volts) Fig. 10. Step response simulation in near end crosstalk for non-optimized TSV pattern Fig. 11. Step response simulation in near end crosstalk for optimized TSV pattern

Conclusion This work investigated the via crosstalk noise under high speed operations and discussed the impacts of various factors affecting crosstalk. An analytical model can be proposed that could capture the induced coupling noise. The coupling and crosstalk can be analyzed from the equivalent circuit of the differential pin pattern and can be applied for the design of crosstalk suppression.

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