Energy Efficient Bandwidth for Electrical Backplanes and Copper Interconnects

Transcription

1 Energy Efficient Bandwidth for Electrical Backplanes and Copper Interconnects Dr. Jeffrey H. Sinsky Optical Subsystems and Advanced Photonics Department, Bell Labs, Alcatel-Lucent

2 Contributors David Neilson, Bell Labs, Alcatel-Lucent Andrew Adamiecki, Bell Labs, Alcatel-Lucent 2 Energy Efficient Backplanes April 2010 J. Sinsky All Rights Reserved Alcatel-Lucent 2010

3 Overview The limitations of copper how far can we go with copper when do we need optics Understanding the fundamental challenges of electrical backplanes and copper interconnects Thinking about electrical transmission lines from a Shannon perspective Using higher order modulation formats the good and the bad Examples of multilevel signaling performance over backplanes and cables Current state of the industry Where we need to go Conclusion 3 Energy Efficient Backplanes April 2010 J. Sinsky All Rights Reserved Alcatel-Lucent 2010

4 The Limitations of Copper Experimental Findings To Date D.T.Neilson, D. Stiliadis, and P. Bernasconi, Ultra-High Capacity " ECOC 2005, Glasgow, UK, September Energy Efficient Backplanes April 2010 J. Sinsky All Rights Reserved Alcatel-Lucent 2010

5 Applications that will require optical interconnects - Distance bandwidth products of over 100 Gb/s m are possible candidates - Distance bandwidth products of over 1Tb/s m will almost certainly be optical! EXAMPLES -distance bandwidth products between 100 Gb/s m and 1Tb/s m Between Racks: 1Gb/s-10Gb/s rates Backplanes: 100Gb/s-1Tb/s rates Linecards: 300Gb/s-3Tb/s rates On chip: 3Tb/s-30Tb/s rates Rates are per waveguide! D.T.Neilson, Challenges for Optical and Electrical Interconnects, WTM 2010 IEEE Photonics Society Winter Topical Meeting on Photonics for Routing and Interconnects, Majorca, Spain, January 12, Energy Efficient Backplanes April 2010 J. Sinsky All Rights Reserved Alcatel-Lucent 2010

6 Understanding the fundamental challenges of electrical backplanes and copper interconnects

7 Electrical Transmission Line Losses α = α c + α d + α r + α l 8.686R αc = Z W where db/unit length ωμ0 Rs = = surface resistance 2σ W = trace width Z = characteristic impedance 0 0 f s αc α d = conductor loss = dielectric loss αr = radiation loss α l = leakage loss ε 1 re ε r tanδ α = 8.686π 1 d ε r ε re λg ε = relative dielectric constant ε r re = effective dielectric constant λ = guided wavelength g tanδ = loss tangent f db/unit length Jia-sheng Hong, M.J. Lancaster, Microwave Filters for RF/Microwave Applications, Wiley, New York, pg Energy Efficient Backplanes April 2010 J. Sinsky All Rights Reserved Alcatel-Lucent 2010

8 Backplane Design Challenges at High Speed Line Card Trace Tx/Rx ASIC (includes via) Controlled impedance must be maintained Cross-talk between pins is difficult to reduce Backplane Trace Connector Line Card Via Backplane Via Backplane PCB AirMax TM 0 db steep roll off from lossy trace FCI Airmax Demo 24 Trace -20 db -40 db -33 db 12.5 GHz narrow resonance from stub effect severe attenuation -60 db ~ 14 GHz Transfer Function The viahole looks like an inductor Unless removed, the unterminated part of the viahole acts as a resonant stub 8 Energy Efficient Backplanes April 2010 J. Sinsky All Rights Reserved Alcatel-Lucent 2010

9 The impact of backplane connectors and dielectric loss Jri Lee, Ming-Shuan Chen, and Huai-De Wang, Design and Comparison of 20-Gb/s Backplane Transceivers for Duobinary, PAM4, and NRZ Data, IEEE Journal of Solid-State Circuits, Vol. 43, No. 9, September Energy Efficient Backplanes April 2010 J. Sinsky All Rights Reserved Alcatel-Lucent 2010

10 Backplane Losses Examples FR4 Backplanes : 5dB/GHz/m 10Gb/s data rate (f=5ghz) 0.8m length : 20dB loss Improved Backplane materials : 1dB/GHz/m 50Gb/s data rate (f=25ghz) 0.8m length : 20dB loss Coax Low loss dielectric : 0.05dB/GHz/m 40Gb/s data rate (f=20ghz) 20m length : 20dB loss Note: Losses calculated at Nyquist frequency (Bitrate/2 for NRZ) D.T.Neilson, Challenges for Optical and Electrical Interconnects, WTM 2010 IEEE Photonics Society Winter Topical Meeting on Photonics for Routing and Interconnects, Majorca, Spain, January 12, Energy Efficient Backplanes April 2010 J. Sinsky All Rights Reserved Alcatel-Lucent 2010

11 Cable Design Challenges at High Speed The The cable cable dilemna Larger diameter less lessloss, loss, worse worsehigh frequency performance Smaller diameter better betterhigh frequency performance, more moreloss ( ) 2 4 { } λ = 2πr 1 (1/ 6)( t/ 2 r ) (7 /120)( t/ 2 r )... *** c m m m where rm = ro + ri t = r r o A non-tem mode will will start start to to propagate at at λ c, c, or or f c f c GHz GHz i /2 ***Green, H., Determination of the Cutoff of the First Higher Order Mode in a Coaxial Line by the Transverse Resonance Technique, IEEE MTT Trans., Vol. 37, No.10, Oct. 1989, pp f c GHz where r i r o π r i r o ε ( r + r ) r o i = inner radius in inches = outer radius in inches 11 Energy Efficient Backplanes April 2010 J. Sinsky All Rights Reserved Alcatel-Lucent 2010

12 Materials For cables Lower loss dielectric materials Clever use of metals that try to equalize the frequency response roll off Example: Gore eye opener cable For Backplanes Lower loss dielectric materials must be cheap and applicable to multilayer assembly Remove woven nature of the dielectric material Example: Dupont is developing dielectric materials that do not exhibit the periodic mismatch of a typical FR4 which results from its woven structure 106 glass 1080 glass Woven-Glass- Non Uniform Aramid reinforcement - More Uniform and Homogenous 12 Energy Efficient Backplanes April 2010 J. Sinsky All Rights Reserved Alcatel-Lucent 2010

13 Thinking about electrical transmission lines from a Shannon perspective

14 Interconnect Channels: Shannon C: Channel capacity (bits/s) B: Channel bandwidth (Hz) SNR: Signal energy / noise energy Shannon capacity: C = B log 2 (1 + SNR) spectral efficiency (bits/s/hz) Error-free not achievable Shannon s limit Error-free achievable SNR (db) Shannon formula assumes optimum constellation and optimum coding of data the best you can do 14 Energy Efficient Backplanes April 2010 J. Sinsky All Rights Reserved Alcatel-Lucent 2010

15 Electrical Interconnects Using Higher order Formats Possible to use higher order signaling to reduce max frequency but requires higher SNR (e.g. 2b/s/Hz requires 5dB improved SNR but only half frequency so lower losses) If we take the FR4 example above 5dB/GHz/m for 0.8m backplane Look at required SNR at launch: this accounts for losses and Shannon Above 2.5Gb/s optimum format is not NRZ a = loss ch l back NRZ Spectral Efficiency (b/s/hz) Operation at 20Gb/s and 40Gb/s may be possible D. T. Neilson, "Photonics for switching and routing," IEEE J. Sel. Topics Quantum Electron. 12, (2006). D.T.Neilson, Challenges for Optical and Electrical Interconnects, WTM 2010 IEEE Photonics Society Winter Topical Meeting on Photonics for Routing and Interconnects, Majorca, Spain, January 12, Energy Efficient Backplanes April 2010 J. Sinsky All Rights Reserved Alcatel-Lucent 2010

16 Choosing a Signaling Format for Energy Efficient Transmission - Tradeoffs Fitting signal bandwidth into optimal portion of the channel response Intelligent transmission of signal energy Sensitivity of format to spectral anomalies Impact on power requirements Increased SNR requirement for higher order constellations Efficiency of required electronics Implementation complexity Cost 16 Energy Efficient Backplanes April 2010 J. Sinsky All Rights Reserved Alcatel-Lucent 2010

17 Signal Bandwidth Compression Spectrally Efficient Formats for Cables and Backplanes Formats Duobinary PAM-4 polybinary PAM-X Pattern dependence issues must be kept in mind Multilevel signaling relocates signal energy to the frequency range with the lowest insertion loss This makes sense for electrical backplanes and cables! H.-J. Goetz, J.H. Sinsky, The Duobinary Format: A New Application for an Idea Published Long Ago, DesignCon 2006, Santa Clara, CA, invited talk. 17 Energy Efficient Backplanes April 2010 J. Sinsky All Rights Reserved Alcatel-Lucent 2010

18 Considerations for Optimal Transmission distortion function Certain formats are more sensitive to the fine structure found in the preferred region. 18 Energy Efficient Backplanes April 2010 J. Sinsky All Rights Reserved Alcatel-Lucent 2010

19 Compare Signaling Architecture Hardware Complexity NRZ Duobinary Jri Lee, Ming-Shuan Chen, and Huai-De Wang, Design and Comparison of 20-Gb/s Backplane Transceivers for Duobinary, PAM4, and NRZ Data, IEEE Journal of Solid-State Circuits, Vol. 43, No. 9, September Energy Efficient Backplanes April 2010 J. Sinsky All Rights Reserved Alcatel-Lucent 2010

20 Compare Signaling Architecture Hardware Complexity (continued) PAM-4 Jri Lee, Ming-Shuan Chen, and Huai-De Wang, Design and Comparison of 20-Gb/s Backplane Transceivers for Duobinary, PAM4, and NRZ Data, IEEE Journal of Solid-State Circuits, Vol. 43, No. 9, September Energy Efficient Backplanes April 2010 J. Sinsky All Rights Reserved Alcatel-Lucent 2010

21 Power Consumption of a Typical 90nm CMOS Buffer as a Function of Bandwidth (simulation) It is important that the hardware required to transmit and receive the hardware is not too complex!! Jri Lee, Ming-Shuan Chen, and Huai-De Wang, Design and Comparison of 20-Gb/s Backplane Transceivers for Duobinary, PAM4, and NRZ Data, IEEE Journal of Solid-State Circuits, Vol. 43, No. 9, September Energy Efficient Backplanes April 2010 J. Sinsky All Rights Reserved Alcatel-Lucent 2010

22 Using Better Materials and Connectors Makes Sense Megtron 6 vs. Taconic Substrates Courtesy of Tyco Electronics 2 db/ghz/m 1 db/ghz/m Taconic Megtron6 Channel bounds OIF CEI-25G-LR (simulation) Backplane thickness 250 mils Daughter card thickness mils Daughtercards have 10 of a pair and backplane has16 total inches of diff pair. Each daughtercard interface has a STRADA Whisper mated connector pair. (total length = 1 meter) STRADA Whisper 22 Energy Efficient Backplanes April 2010 J. Sinsky All Rights Reserved Alcatel-Lucent 2010

23 Examples of Backplane and Copper Interconnect Signaling Techniques

24 Examples PAM-4 backplane (5 Gb/s) Duobinary backplane (25 Gb/s) Duobinary cable (40 Gb/s) NRZ with equalization (25 Gb/s) 24 Energy Efficient Backplanes April 2010 J. Sinsky All Rights Reserved Alcatel-Lucent 2010

25 PAM-4 Example Stonick, J.T.; Gu-Yeon Wei; Sonntag, J.L.; Weinlader, D.K.;, "An adaptive PAM-4 5- Gb/s backplane transceiver in 0.25-μm CMOS," Solid-State Circuits, IEEE Journal of, vol.38, no.3, pp , Mar Energy Efficient Backplanes April 2010 J. Sinsky All Rights Reserved Alcatel-Lucent 2010

26 Electrical Duobinary over Backplanes and Cables How it works We take advantage of the natural spectral roll off response of the backplane channel to convert standard NRZ data to duobinary data, effectively using the channel as part of the transmitter. At the receiver, a quasi-digital duobinary-to-binary converter is used to regenerate NRZ data. We were the first to demonstrate GHz-rate duobinary data transmission over FR4 backplanes and the first to demonstrate 25 Gb/s data transmission over an FR4 backplane H ( ω) H ( ω) H ( ω) = H ( ω) FIR Ch EQ duo 25 Gb/s Example Avoids resonances Sinsky, J.H.; Duelk, M.; Adamiecki, A., "High-speed electrical backplane transmission using duobinary signaling," Microwave Theory and Techniques, IEEE Transactions on, vol.53, no.1pp , Jan Energy Efficient Backplanes April 2010 J. Sinsky All Rights Reserved Alcatel-Lucent 2010

27 10 Gb/s Backplane Transmission Results Pre-emphasized Signal Into the backplane Tyco Quadroute Backplane (34 trace) Xaui Reference Backplane First demonstrati on of GHzspeed duobinary signaling over a backplane Board Name Quadroute Nelco Dielectric Trace Geometry (width, space, width) 4,6,4 (mils) Connector Type HM-ZD 34 backplane channel BER <10-13 Duobinary decision thresholds J.H. Sinsky, A. Adamiecki, M. Duelk, 10-Gb/s Electrical Backplane Transmission using Duobinary Signaling, IMS-2004, Fort Worth, TX, June Gb/s Duobinary backplane output PRBS 23 Measurement 27 Energy Efficient Backplanes April 2010 J. Sinsky All Rights Reserved Alcatel-Lucent 2010

28 25 Gb/s Backplane Transmission Results (4 x 25 Gb/s) Pre-emphasized Signal Into the backplane PRBS 7 AIRMAX Backplane S21 Magnitude [db] Board Name 2 Line Cards PCB Material Nelco Rogers RO4350 Line Lengths 7.5cm, 25cm 50cm, 75cm 5cm each Layers 20 2 Connector Type AirMax VS AirMax VS 0 35cm (14'') cm (24'') Frequency [GHz] Line Card Adamiecki, A.; Duelk, M.; Sinsky, J.H., "25 Gbit/s electrical duobinary transmission over FR-4 backplanes," Electronics Letters, vol.41, no.14pp , 7 July First demonstration of 25 Gb/s data transmission over an FR4 backplane 0.2V/DIV 25 Gb/s Duobinary backplane output PRBS 7 Measurement 65mV/DIV BER < ps/DIV 24 backplane channel 10ps/DIV 28 Energy Efficient Backplanes April 2010 J. Sinsky All Rights Reserved Alcatel-Lucent 2010

29 40 Gb/s over an 24.4 meters of SMA Coaxial Cable Pre-emphasized Signal Into the cable First demonstration of 40 Gb/s duobinary data transmission over a 24.4 m coax cable Manufacturer Outer Diameter Dielectric Operating Bandwidth Length MIDISCO MegaPhase Air/PTFE Micro-porous PTFE Tape DC-18 GHz DC-24 GHz 40 feet 40 feet 24.4 meter coax cable channel BER <10-14 J.H. Sinsky, A. Konczykowska, A. Adamiecki, F. Jorge, M. Duelk, 39.4 Gb/s Duobinary Transmission over 24.4 meters of Coaxial Cable using a Custom Indium Phosphide Duobinary-to- Binary Converter Chip, accept IEEE Trans. On Microwave Theory and Techniques, Dec or Jan Gb/s Duobinary cable output PRBS 7 Measurement 29 Energy Efficient Backplanes April 2010 J. Sinsky All Rights Reserved Alcatel-Lucent 2010

30 NRZ with Equalization Example (25 Gb/s) Tyco Designcon Gb/s 18 of Megtron 6 (including daughtercards) with Avago silicon Both daughtercards use Tyco s STRADA Whisper connectors on them Courtesy of Tyco Electronics 30 Energy Efficient Backplanes April 2010 J. Sinsky All Rights Reserved Alcatel-Lucent 2010

31 Current State of the Industry OIF Looking at 25 Gb/s Long Reach over backplane (CEI-25G-LR) Have been exploring NRZ signaling with pre-emphasis and equalization IEEE 802.3ba - 40Gb/s and 100Gb/s Ethernet Task Force Provide Physical Layer specifications which support 40 Gb/s operation over at least 10km on SMF at least 100m on OM3 MMF at least 7m over a copper cable assembly at least 1m over a backplane Provide Physical Layer specifications which support 100 Gb/s operation over: at least 40km on SMF at least 10km on SMF at least 100m on OM3 MMF at least 7m over a copper cable assembly 31 Energy Efficient Backplanes April 2010 J. Sinsky All Rights Reserved Alcatel-Lucent 2010

32 Where we need to go Need to focus more on energy efficiency Intelligent use of channel Use better channels! They exist! Lower loss dielectrics Tighter more random weaves Improve metallization roughness spec Once materials are improved, backplane connectors will become the bottleneck! Innovative designs are needed very challenging Consider low frequency equalization carefully for multi-level formats There may be more sensitivity to gain and phase variations 32 Energy Efficient Backplanes April 2010 J. Sinsky All Rights Reserved Alcatel-Lucent 2010

33 Conclusion Electrical backplanes and interconnects are not dead yet!! Electrical backplane transmission at 25 Gb/s should be possible up to 1 meter An optimal combination of multi-level formats, improved dielectric material, and improved connectors should pave the way for progress For coaxial cables, rates to 40 Gb/s should be possible in a commercial setting over many meters An exciting challenge would be to push backplane line rates to 40 Gb/s Would require innovation in connectors and connection techniques between backplane layers 33 Energy Efficient Backplanes April 2010 J. Sinsky All Rights Reserved Alcatel-Lucent 2010