High speed digital signal path design for a 40 gb s optical receiver
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High Speed Digital Signal Path Design for a 40 Gb /s Optical Receiver. European ADS User’s Group Meeting Boeblingen , May 14-15 2009. Contents. Trends in Fiber Optics Optical Receiver Modul with 4x 10Gb/s High Speed Signal Path Transimpedance Amplifier (TIA) Output stage IC Bondwire

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High Speed Digital Signal Path Design for a 40 Gb /s Optical Receiver

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High speed digital signal path design for a 40 gb s optical receiver

High Speed Digital Signal Path Design for a 40 Gb/s Optical Receiver

European ADS User’s Group Meeting

Boeblingen, May 14-15 2009

KD

5/18/2009


Contents

Contents

  • Trends in Fiber Optics

  • Optical Receiver Modul with 4x 10Gb/s

  • High Speed Signal Path

    • Transimpedance Amplifier (TIA) Output stage

    • IC Bondwire

    • Package Feedthrough

    • Flex Foil Circuit

    • Test board interconnection & Test Board

  • RF Path in Frequency Domain

  • RF Path in Time Domain

  • Measurement Data: Eye diagram & TDR

  • Conclusion


  • Trends in fiber optics

    Trends in Fiber Optics

    Standardization Activities

    • IEEE HSSG10G  40 G  100 G

    • QSFP – MSA  4x 5 G; 4 x 8 G; 4 x10 G

    • USB 3.0  5G

    • XMD – MSA  ROSA/TOSA up to 10 G

    • XLMD –MS  ROSA/TOSA up to 40 G

    • Active Optical Cable  12 x 10G


    Trends in fiber optics1

    Trends in Fiber Optics

    100 G and 40 G Form Factors for Transceivers

    4x10Gb/s


    Optical receiver module with 4x 10gb s

    Optical Receiver Module with 4x 10Gb/s

    Fiber

    Flex Foil

    Package

    www.cubeoptics.com


    High speed signal path

    High Speed Signal Path

    Flex foil – Test Board transition

    RX Module

    Bottom side up

    Flex foil

    Test Board

    SMD Connector


    High speed signal path1

    High Speed Signal Path

    Signal path divided in section to create models

    RF out

    RF in

    50Ohm

    Packageto

    FlexFoil

    transition

    Flexto

    Test Board

    transition

    Test

    board

    Flex foil

    circuit

    TIA output

    stage

    Bond wire

    50Ohm

    V0

    Vtia

    Vbw

    Vpkg

    Vflex

    Vtb

    Vout


    Tia output stage linear circuit model

    TIA Output Stage: Linear Circuit Model

    TIA Chip

    Channel

    simulation

    source

    linear transistor model

    CML output stage


    Bond wire model 3d em simulation model

    Bond Wire Model: 3D EM Simulation Model

    TIA

    Bond wire

    Glass

    Metal pin

    (differential feedthrough)

    S-Parameter extracted

    from EM simulation

    3D Model


    Package feedthrough 3d em simulation

    Package Feedthrough: 3D EM Simulation

    Metal base

    Glass

    Metal Pins

    Mag (SDD11)

    Flex foil circuit

    S-Parameter extracted

    from EM simulation


    Flex foil circuit 2 5d em simulation model

    Flex Foil Circuit: 2.5D EM Simulation Model

    Flex foil circuit layout in ADS

    one RF path copied and simulated in Momentum

    Polyimide: 50um, Cu T=36um, 50um Cover layer

    Coupled microstrip: w=70um, s=250um, Zdiff=100


    Test board interconnection

    Test Board Interconnection

    RF critical section copied to

    Momentum (use Utility)

    Layout in Allegro PCB

    Flex circuit on top

    Test board

    Momentum 3D view


    Test board ads line models

    Test Board: ADS Line Models

    line splitter(*)

    Microstrip line

    differential line

    (*) Line splitter model

    created with Momentum

    PCB cut view


    Rf path in frequency domain

    RF Path in Frequency Domain

    TIA Output stage omitted

    Simulation set up in ADS


    Rf path in frequency domain1

    RF Path in Frequency Domain

    Vbw

    Vpkg

    Vflex

    +1.2dB

    loss

    RF out

    RF in

    50Ohm

    Packageto

    FlexFoil

    transition

    Flexto

    Test Board

    transition

    Test

    board

    Flex foil

    circuit

    TIA output

    stage

    Bond wire

    50Ohm

    V0

    Vtia

    Vbw

    Vpkg

    Vflex

    Vtb

    Vout

    Vtb

    Vout

    each section

    ideal terminated

    +1.8dB

    loss


    Rf path in time domain

    RF Path in Time Domain

    Models defined in frequency domain

    and simulated in time domain using convolution


    Rf path in time domain1

    RF Path in Time Domain

    RF out

    RF in

    50Ohm

    Packageto

    FlexFoil

    transition

    Flexto

    Test Board

    transition

    Test

    board

    Flex foil

    circuit

    TIA output

    stage

    Bond wire

    50Ohm

    V0

    Vtia

    Vbw

    Vpkg

    Vflex

    Vtb

    Vout


    Eye diagram measurement setup

    Eye Diagram Measurement Setup


    Measurement data eye diagram

    Measurement Data: Eye Diagram

    Flex line with Cu

    receive opt. Power -12dBm

    sensitivity -18dBm (BER=10E-12)

    Flex line with Ni/Au plating

    Flex line has Ni/Au plating

    Ni is a ferromagnetic conductor

     smaller skin depth = higher loss


    Measurements data tdr

    Measurements Data: TDR

    Flex ctr

    Test Board

    SMA

    AC Cap.

    Transition to Flex


    Conclusion

    Conclusion

    • First samples: full functional, acceptable sensitivity

    • Bond wire interconnection & package ok

    • Issues identified by measurements and simulations:

      • Test board to flex circuit transition too much reflection

      • Flex circuit loss to high

      • Test board traces too long


    Results after redesign

    Results after Redesign

    • Test board to flex circuit transition improved (new concept)

    • Flex circuit loss improved (no cover layer)

    • Test board traces shorted (approx. half length)

    sensitivity < -19.0dBm @ BER = 1E-12 (1 to 1.5dB improvement)


    Product design methodology

    Product Design Methodology

    • Predict performance early in the design cycle by creating models for each component, critical net and entire system and by performing local and system simulation.

    • Use measurements throughout the design cycle to reduce risk and increase confidence to the quality of predictions.

    Eric Bogatin


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