® WPD WORKSTATION PRODUCTS DIVISION 1 Page 1 IEEE EPEP2000 Via and Return Path Discontinuity Impact on High Speed Digital Signal Qinglun Chen, Intel WPD Jin Zhao, Sigrity Inc. Contributor: Weimin Shi, Intel DPG, Raymond Chen (Sigrity) Chi-te Chen Intel WPD

® WPD WORKSTATION PRODUCTS DIVISION 2 Page 2 IEEE EPEP2000 1)The motivation of this study 2)How via impact on high speed digital signal 3)How Signal return path discontinuity impact on high speed digital signal 4)Correlation and measurements 5)Summary Agenda

® WPD WORKSTATION PRODUCTS DIVISION 3 Page 3 IEEE EPEP2000 Motivations of This Study Rambus needs less than 5 ps skew accuracy and +/- 125 ps skew budget. What are the major skew contributors for Rambus channel interconnection? Via discontinuity and coupling Return path discontinuity Manufacturing variation Impedance discontinuity Buffer Strength difference Cross talking ---even and odd modes Load variation

® WPD WORKSTATION PRODUCTS DIVISION 4 Page 4 IEEE EPEP2000 Via Discontinuity How via length impact the signal wave form and delay? How via coupling impact the signal wave form and delay? How termination via impact the signal wave form? Test Board for Rambus Study

® WPD WORKSTATION PRODUCTS DIVISION 5 Page 5 IEEE EPEP2000 How via length impact on high Speed digital signal quality Signal trace GND Via Via Inductance depending on its length -> impedance either

® WPD WORKSTATION PRODUCTS DIVISION 6 Page 6 IEEE EPEP2000 Waveform and Delay Comparison

® WPD WORKSTATION PRODUCTS DIVISION 7 Page 7 IEEE EPEP2000 How via coupling impact on high Speed digital signal quality Signal trace GND Via even coupling  increase via inductance  increase impedance Via odd coupling  decrease via inductance  decrease impedance

® WPD WORKSTATION PRODUCTS DIVISION 8 Page 8 IEEE EPEP2000 Via Coupling impact on waveform and Delay

® WPD WORKSTATION PRODUCTS DIVISION 9 Page 9 IEEE EPEP2000 Gnd Pwr ~ 35 Ohm28 OhmVcc Gnd Pwr ~ 35 Ohm28 OhmVcc Figure 6. Configuration of Rambus signal net How termination via impact the signal wave form?

® WPD WORKSTATION PRODUCTS DIVISION 10 Page 10 IEEE EPEP2000

® WPD WORKSTATION PRODUCTS DIVISION 11 Page 11 IEEE EPEP2000 PCB Signal Return Path Discontinuity How does a power reference plane impact the signal wave form and delay? How does via return path impact the signal wave form and delay? What is the difference between single line vs multiple line switching for RPD? How do different layer traces impact the signal wave form and delay?

® WPD WORKSTATION PRODUCTS DIVISION 12 Page 12 IEEE EPEP2000 How a power reference plane impact the signal wave form and delay? Signal trace GND VCC Via AC path through inductance and capacitance Local capacitance is frequency dependent Current have to flow to the ground plane through local capacitance and induce imaging current Referring a power plane will create return path discontinuity

® WPD WORKSTATION PRODUCTS DIVISION 13 Page 13 IEEE EPEP2000 Return Path Discontinuity & Via Coupling impact on waveform and Delay

® WPD WORKSTATION PRODUCTS DIVISION 14 Page 14 IEEE EPEP2000 What is the difference between single line vs multiple line switching for RPD? At Receivers: 1 line switching on S1 1 line switching on s6 8 line switching on s6

® WPD WORKSTATION PRODUCTS DIVISION 15 Page 15 IEEE EPEP2000 How via return path impact on high Speed digital signal quality Signal trace GND VCC GND Via Delay order: near ground via, far ground via, no ground via GND

® WPD WORKSTATION PRODUCTS DIVISION 16 Page 16 IEEE EPEP2000 How Ground Via impact on Skew and Waveform

® WPD WORKSTATION PRODUCTS DIVISION 17 Page 17 IEEE EPEP2000 Measurement Results for Four layers with 3 Line coupling

® WPD WORKSTATION PRODUCTS DIVISION 18 Page 18 IEEE EPEP2000 OR840 WS Board Benefits From Fundamental Studies With Speed97 More than 4000 outrigger system boards are shipped per week Fundamental studies: 1. Return path; 2. Via coupling; 3. Die-to-Termination channel analysis This is a very competitive product: Rambus IS on 4 Layer stack-up That is why IBM has ordered a big volume S1 GND S3 VCC Rambus signals Outrigger Board Stack-up:

® WPD WORKSTATION PRODUCTS DIVISION 19 Page 19 IEEE EPEP2000 Correlation

® WPD WORKSTATION PRODUCTS DIVISION 20 Page 20 IEEE EPEP2000 Power plane as ground return test pattern Via coupling test pattern Propagation delay test pattern for manufacturing variation Via characterization Pattern Test Board For Correlation(1998) Via characterization pattern

® WPD WORKSTATION PRODUCTS DIVISION 21 Page 21 IEEE EPEP2000 S1 GND S3 S4 VCC S6 400 mils 62 mils 100 mils 50 ohm Trace Via Via Coupling Pattern

® WPD WORKSTATION PRODUCTS DIVISION 22 Page 22 IEEE EPEP2000 Red Line --- no coupling, Blue Line -----Odd coupling Test Board Measurement of Via Even Mode Coupling

® WPD WORKSTATION PRODUCTS DIVISION 23 Page 23 IEEE EPEP2000 Red Line --- no coupling, Blue Line -----Odd coupling Test Board Measurement of Via Odd Mode Coupling

® WPD WORKSTATION PRODUCTS DIVISION 24 Page 24 IEEE EPEP2000 Via Coupling Skew Measurement and Simulation (Even/odd Modes) Via coupling skew depends on input signal skew

® WPD WORKSTATION PRODUCTS DIVISION 25 Page 25 IEEE EPEP2000 S1 GND S3 S4 VCC S6 400 mils 62 mils 50 ohm Trace Via Two Series Via Patterns for Correlation S1 GND S3 S4 VCC S6 62 mils

® WPD WORKSTATION PRODUCTS DIVISION 26 Page 26 IEEE EPEP2000 Speed97 Simulation Vs TDR Measurement Pattern 1 Red Line --- Measurement, Blue Line -----Speed97 ( done in 12/1998 at New York University at Binghamton by Weimin Shi )

® WPD WORKSTATION PRODUCTS DIVISION 27 Page 27 IEEE EPEP2000 Speed97 Simulation Vs TDR Measurement Pattern 2 Red Line --- Measurement, Blue Line -----Speed97 ( done in 12/1998 at New York University at Binghamton by Weimin Shi )

® WPD WORKSTATION PRODUCTS DIVISION 28 Page 28 IEEE EPEP2000 Summary Via discontinuity and coupling become a major signal skew contributor for high speed digital signals Power reference plane is another major signal skew contributor for high speed digital signals Synchronized signals should reference a same ground plane to avoid additional signal skew Return path discontinuity is due to non-uniform inductance and capacitance in signal paths