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Providing Infrastructure for Optical Communication Networks. Prof. Michael Green Dept. of EECS Henry Samueli School of Engineering EECS 294 Colloquium 4 October 2006. This presentation can be found at: - PowerPoint PPT Presentation


  • Providing Infrastructure for Optical Communication NetworksProf. Michael GreenDept. of EECSHenry Samueli School of Engineeringmgreen@uci.eduEECS 294 Colloquium4 October 2006This presentation can be found at:

  • Friday, March 7 2003

  • Advantages of Optical Fibers over Copper Cable Very high bandwidth (bandwidth of optical transmission network determined primarily by electronics) Low loss Interference Immunity (no antenna-like behavior) Lower maintenance costs (no corrosion, squirrels dont like the taste) Small & light: 1000 feet of copper weighs approx. 300 lb.1000 feet of fiber weighs approx. 10 lb. Different light wavelengths can be multiplexed onto a single fiber: Dense Wavelength Division Multiplexing (DWM) 10Gb/s transmission networks now being deployed; 40Gb/s will be here soon.

  • Protocols for High-Speed Optical NetworksSynchronous Optical Network (SONET): Provides a protocol for long-haul (50-100km) wide-area netework (WAN) fiber transmission Basic OC-1 rate is 51.84Mb/s OC-48 (2.5Gb/s) & OC-192 (10Gb/s) are commonGigabit/10 Gigabit Ethernet (IEEE Standard 802.3): Ethernet was invented in 1973 at Xerox PARC(ether is the name of the medium through which E/M waves were thought to travel) Provides a protocol for local-area network (LAN) copper or fiber transmission 1 Gb/s links can be transmitted over twisted-pair copper 10 Gb/s links can be transmitter over copper (short lengths) or fiber.

  • Fiber Channel: Often used for Storage Area Networks (SAN); allows fast transmission of large amounts of data across many different servers. Currently 1-4 Gb/s is deployed; 8Gb/s will arrive soon.

  • Some SAN TerminologyJBOD: Just a Bunch Of DisksRefers to a set of hard disks that are not configured together.

    RAID: Redundant Array of Independent (or Inexpensive?) DisksMultiple disk drives that are combined for fault tolerance and performance. Looks like a single disk to the rest of the system. If one disk fails, the systems will continue working properly.

  • Blade Servers vs. Regular ServersSee: full article.

  • Barcelona, Spain:MareNostrum supercomputer cluster (2282 Blade servers)Housed in Chapel Torre Girona (Technical Univ. of Catalonia)

  • Characteristics of Broadband Signals & Circuits

    Standard analog circuit applications: Continuous-time operation Precision required in signal domain (i.e., voltage or current) Dynamic range determined by noise & distortion

    Broadband communication circuits: Discrete-time (clocked) operation Precision required in time domain (low jitter) Bilevel signals processed

    Primarily digital (i.e., bilevel) operation but high bit rate (multi-Gb/s) dictates analog behavior & design techniques.

  • Typical broadband data waveform:Length of single bit = 1 Unit Interval (1 UI)An eye diagram maps a random bit sequence to a regular structure that can be used to analyze jitter.

  • Close-up of eye diagram:voltage swing1 UIZero crossingstrise = tfall

  • What is Jitter?Jitter is the short-term variation of the significant instants of a digital signal from their ideal positions in time.Jitter normally characterizes variations above 10Hz; variations below 10Hz are called wander.Phase noise (frequency domain)Jitter (time domain)Bit Error-Rate (end result of phase noise & jitter)The effects of these variations are measured in 3 ways:

  • Types of JitterRandom Jitter (RJ)Originates from external and internal random noise sourcesStochastic in nature (probability-based)Measured in rms unitsObserved as Gaussian histogram around zero-crossingGrows without bound over timeHistogram measurement at zero crossing exhibiting Gaussian probability distribution

  • Types of Jitter (cont.)Deterministic Jitter (DJ)Originates from circuit non-idealities (e.g., finite bandwidth, offset, etc.)Amount of DJ at any given transition is predictableMeasured in peak-to-peak unitsBounded and observed in various eye diagram signatures

    Different types of DJ:Intersymbol interference (ISI)Duty-cycle distortion (DCD)Periodic jitter (PJ)

  • Consider a 1UI output pulse from a buffer:a) Intersymbol interference (ISI)

  • 001101ISI (cont.)Consider 2 different bit sequences:t = ISISteady-state not reachedat end of 2nd bit2 output sequencessuperimposedISI is characterized by a double edge in the eye diagram. It is measured in units of ps peak-to-peak.

  • Double-edgeEffect of ISI on eye diagram:

  • Occurs when rising and falling edges exhibit different delaysCaused by circuit mismatchesNominal data sequenceData sequence with early falling edges& late rising edgest = DCDEye diagram with DCDb) Duty cycle distortion (DCD)

  • c) Periodic Jitter (PJ)Timing variation caused by periodic sources unrelated to the data pattern.Can be correlated or uncorrelated with data rate.Synchronized dataexhibiting correlated PJUncorrelated jitter (e.g., sub-rate PJ due to supply ripple) affects the eye diagram in a similar way as RJ.

  • R0TProbability of sample at t > t0 from left-hand transition:Probability of sample at t < t0 from right-hand transition:Jitter and Bit Error Rate

  • Total Bit Error Rate (BER) given by:

  • t0 (ps)log BERExample: T = 100ps(64ps eye opening)(38ps eye opening)log(0.5)

  • Bathtub CurvesThe bit error-rate vs. sampling time can be measured directly using a bit error-rate tester (BERT) at various sampling points.Note: The inherent jitter of the analyzer trigger should be considered.

  • Benefits of Using Bathtub Curve MeasurementsCurves can easily be numerically extrapolated to very low BERs (corresponding to random jitter), allowing much lower measurement times.Example: 10-12 BER with T = 100ps is equivalent to an average of 1 error per 100s. To verify this over a sample of 100 errors would require almost 3 hours!t0 (ps)

  • Deterministic jitter and random jitter can be distinguished and measured by observing the bathtub curve.

  • Advantages of Using CMOS Fabrication Process Compact (shared diffusion regions)

    Very low static power dissipation

    High noise margins (nearly ideal inverter voltage transfer characteristic)

    Very well modeled and characterized

    Inexpensive (?)

    Mechanically robust

    Lends itself very well to high integration levels

    SiGe BiCMOS has many advantages but is a generation behind currently available standard CMOS

  • CMOS gates generate and are sensitive to supply/ground bounce.Series R & L cause supply/ground bounce.Resulting modulation of transistor Vts results in jitter.

  • data inclock in Rs = 0Ls = 0clock out clock out Rs = 5WLs = 5nHclock out data outdata out Rs = 5W Ls = 5nH

  • Inverter based on differential pair: Differential operation Inherent common-mode rejection Very robust in the presence of common-mode disturbances (e.g., VDD/VSS bounce)Current-mode logic (CML)

  • data inclock in Rs = 0Ls = 0clock out clock out Rs = 5WLs = 5nHclock out data outdata out Rs = 5W Ls = 5nH

  • Research TopicsBiCMOS 10Gb/s Adaptive Equalizer

    A Novel CDR with Adjustable Phase Detector Characteristics

    A Distributed Approach to Broadband Circuit Design

  • Research Topics

    BiCMOS 10Gb/s Adaptive EqualizerEvelina Zhang, Graduate Student Researcher

    A Novel CDR with Adjustable Phase Detector Characteristics

    A Distributed Approach to Broadband Circuit Design

  • Cable ModelCopper CableWhere: L is the cable length a is a cable-dependent characteristicshorter cablelonger cablelonger cableshorter cable1G10Gf+100-10-20-30magnitude (dB)100M1G10Gf100M0-100-200-300phase (deg)

  • Motivation

    Reduce ISIImprove receiver sensitivity40414243t (ns)40414243t (ns)0.50-0.5input waveform (V)390.30-0.339output waveform (V)100200300t (ps)0100200300t (ps)00.50-0.50.30-0.3input eyeoutput eye

  • Adaptive EqualizerImplemented in Jazz Semiconductor SiGe process: 120GHz fT npn 0.35m CMOS

  • Equalizer Block Diagram

  • Feedforward Path

  • f (Hz)VcontrolFFE Frequency Response

  • ISI & Transition Timeteq = 75psPW = 86psteq = 60psPW = 100ps2. (ns)-0.300.3VFFE Simulations indicate that ISI correlates strongly with FFE transition time teq.

    Optimum teq is observed to be 60ps.teq = 45psPW = 108ps

  • Slicer

  • Feedback Path

  • Transition Time DetectorDC characteristic:Transient Characteristic:t Rectification & filtering done in a single stage.(a)(b)(a)(b)

  • Integrator

  • Detector + IntegratorslopedetectorslopedetectorFromSlicertslicer=60psFromFFEtFFEVcontrol+_0102030405060400-4020-20-60t (ns)Vcontrol (mV)60ps45ps15ps75ps90psFFE transitionTime tFFE

  • System Analysis+_KdKdKeqtslicerteqdetectordetectorfeedforwardequalizerintegratorH(s)VcontrolKeq = 1.5 ps/mVKd = 2.5 mV/pstint = 75ns

  • Measurement SetupDie under test231 PRBS signalapplied to cableEQ inputsEQ outputs

  • Eye Diagrams4-footRU256 cable15-footRU256 cableEQ inputEQ output4.0ps rms jitter3.9ps rms jitter

  • Summary of Measured Performance

    Supply voltage3.3VPower Dissipation350mW(155mW not including output driver)Die Size0.81mm X 0.87mmOutput Swing490mV single-ended p-pRandom Jitter4.0ps rms (4-foot cable)3.9ps rms (15-foot cable)

  • Ongoing ResearchInvestigate transition detector mor


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