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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

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 HSSG 10G  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

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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