Bell Labs, Lucent Technologies - Fci.com

Scalability of Duobinary 

Signaling to 25 Gb/s 

for 100 GbE Applications 

A. Adamiecki, M. Duelk, J. Sinsky, M. Mandich 

Bell Labs, Lucent Technologies 

IEEE 802.3ap Task Force November 2004 slide 1

Supporters 

FCI Communications Corp. 

– Dana Bergey ? 

– XXXXXXXXXXX ? 

VITESSE, Corp. 

– XXXXXXXXXXX 

– XXXXXXXXXXXXXX 


Talk Outline: 

Introduction - motivation for 25Gb/s experiment 

Measurements Test Setup 

Key Hardware Components 

– 25Gb/s Duobinary to NRZ Decoder 

– Backplane designed for 10Gb/s supplied by FCI 

Communications 

Measurement Results 

Simulation and Measurements data comparison 

Conclusions 


Motivation for 25 Gb/s experiment 

Address scalability of 10Gb Ethernet backplane 

signaling choices to next generation technology node 

Next logical rate for Ethernet is 100 Gb/s Ethernet 

Four lane PHY for 100 GbE would be 4 x 25 Gb/s 

NRZ signaling at 10-12.5 Gb/s has been demonstrated 

over good channels 

Duobinary electrical signaling is the obvious solution for 

25 Gb/s electrical transmission because of 2X 

bandwidth compression 


Backplane channel characteristics reveal 

need for bandwidth compression to 

achieve 25Gb/s 

Example of back drilled backplane with improved channels: 

24” link where notch due to stub effects moved above 10GHz 

33dB down @ 12.5GHz, beyond 15 GHz just a noise. noise. 

Achieving 25Gb/s over this channel 

• Need bandwidth compression 

• Need maximum eye opening for 

given voltage swing 

• Duobinary signaling does both! 


25 Gb/s Measurement Test Setup 

Half Rate 

Clock 

12.5 GHz 

25 Gb/s 

NRZ PRBS 

Source 

FIR 

Filter 

Optional 

Amp 

Passive FIR 

Backplane 

+ 2 Line 

Cards 

Duobinary 

Duobinary 

Decoder 

V1 V2 

Thresholds 

Adjustment 

NRZ 

25 Gb/s 

DEMUX 

1:4 

BERT 

@ 6.25 Gb/s 

Agilent Scope 

86100B 


25 Gb/s Duobinary-to-Binary Decoder 

Basic Concept Physical implementation 

Delay Lines – used to balance the 

different electrical lengths of various 

coaxial components 


25 Gb/s Transmitter: 

PRBS with 2-tap Passive FIR Filter 

Passive FIR 


FCI AirMax 10G Demo Backplane + 2 Line 

Cards 

Board 

Name 

AIRMAX 

Backplane 

2 Line 

Cards 

PCB 

Material 

Nelco 

4000-6 

Rogers 

RO4350 

Line 

Lengths 

7.5cm, 25cm, 

50cm, 75 cm 

5 cm each 

Layers Connector 

Type 

20 

2 

AirMax VS 

AirMax VS 

Line Card: Bottom View 

Line Card: Top View 


Trace Lengths Selected for 25Gb/s Transmission 

Experiment: 14’’ (35cm) & 24’’ (60cm) Link 

S21 Magnitude [dB] 

0 

-5 

-10 

-15 

-20 

-25 

-30 

-35 

-40 

-45 

-50 

-55 

24'' (60 cm) 

0 2 4 6 8 10 12 14 16 18 20 22 24 

Frequency [GHz] 

differential 

single-ended 

14'' (35 cm) 


Measurement Results: 14’’ (35cm) Link 

FIR: -9.4dB, 9.4dB, 60ps PRBS 2 7-1 Pre-emphasized data. 

Backplane drive 

amplitude: 360 mVpp 

Backplane outputs: 

190 mVpp amplitude (eye ~30mV) 

PRBS 2 15 15-1 IEEE 802.3ap Task Force November 2004 slide 11

Measurements & Simulations Comparison 

14’’ (35cm) Link 

After FIR Filter (Backplane drive) 

measurement PRBS 7 simulation PRBS 7 

80 mV/DIV, 20 ps/DIV 

2-tap FIR: 60ps, -9.4dB 





14’’ (35cm) Link 

After Backplane PRBS 7 

measurement simulation 



Eye opening: 30mVpp / 40mVpp 



Eye opening: 2 x 42 mVpp 



14’’ (35cm) Link 

measurement 



Eye Openings: 2x25 mVpp 

After Backplane PRBS 15 

simulation 



Eye Openings: 2x31 mVpp 



PRBS 7 

PRBS 15 

NOTE: Duobinary Decoder was working 

at the limit of its sensitivity since the 

backplane was driven only with 360mVpp 

single ended drive! 

Duobinary Decoder NRZ 

Output @ 25 Gb/s 

Demuxed NRZ Data @ 6.25Gb/s 

Performance at 25 Gb/s 

•BER @ PRBS 7 < 10 -13 * 

•BER @ PRBS 15 < 10 -13 * 

* time limited measurement 


Measurement Results : 24”(60cm) Link 

2-tap FIR filter + amplifier 

(single ended drive) 

Backplane Input 

Pre-emphasized TX data 

FIR Filter: -6 6 dB, 60 ps 

Amplitude: 1.2Vpp 

Backplane Output 

Amplitude: 280mVpp 

Eye opening: 2x30mV 



24’’ (60cm) Link 

measurement 

XXX mV/DIV, 20 ps/DIV 


After FIR Filter, PRBS 7 

simulation 





24’’ (60cm) Link: Backplane Outputs 


Measurement PRBS 7 

Measurement PRBS 15 

100 mV/DIV 10 ps/DIV 

Simulation PRBS 7 

Simulation PRBS 15 



40ps/DIV 

60mV/DIV 

PRBS 7 

Demuxed NRZ Data @ 6.25Gb/s 

20ps/DIV PRBS 15 

Duobinary Decoder NRZ 

Output @ 25 Gb/s 


•BER BER @ PRBS 7 < 10 -13 13 * 

•BER BER @ PRBS 15 < 3x10 -10 10 ** 


** this BER could be improved by using 

more taps to cancel the post-cursors post cursors (DFE 

or pre-emphasis) pre emphasis) and an FFE to cancel the 

pre-cursor; 

pre cursor; 


Test Results Summary 

Trace Length 

Data Rate 

PRBS Sequence 

Backplane Single 

Ended drive 

amplitude 

Bit Error Rate 

FCI Backplane 

Link 

FIR Architecture 

24 inches (60cm) 

2 7 -1 

< 10 -13 

25 Gb/s 

1.2 Vpp 

2 15 -1 

< 3x10 -10 

Slot2Mod4_D5 to 

Slot15Mod4_J5 

2-tap (-6dB, 60ps) 

14 inches (35cm) 

2 7 -1 

< 10 -13 

25Gb/s 

360 mVpp 

2 15 -1 

< 10 -13 

Slot7Mod6_D5 to 

Slot10Mod6_J5 

2-tap (-9.4dB, 60ps) 


Conclusions 

Using duobinary signaling, we have demonstrated 25 

Gb/s electrical transmission over 14” and 24” links that 

include a backplane, 2 connectors and 2 line cards 

Duobinary signaling should enable 25 Gb/s signaling over 

higher performance backplanes and connectors 

Improved performance at 25Gb/s should be realizable using, 

e.g., receiver equalization and lower loss backplane materials 

Duobinary signaling offers realistic possibility for scaling 10 

GbE backplane signaling technology to 100 GbE 


Backup Slides 


FCI AIRMAX DEMO Backplane 


FCI Backplane Channels 

(includes line cards)* Total link lengths: 

7”, 14”, 24”, 33” 

dB(_33inch..S(2,1)) 

dB(_24inch..S(2,1)) 

dB(_14inch..S(2,1)) 

dB(_7inch..S(2,1)) 

0 

-10 

-20 

-30 

-40 

-50 

-60 

-70 

Forward transmission, dB 

Traces selected for test 

0 5 10 15 20 25 

freq, GHz 

*Note: Backplane material is Nelco N4000-6 and line cards are 

made from Rogers RO4350. Single ended measurements. 


Selected Traces: 

• 35 cm (Slot7Mod6_D5 ( Slot7Mod6_D5 to Slot10Mod6_J5 Signal 

Layer7) 

Total length: 14” ( 25cm + 2 Line cards, each 5cm) 

• 60 cm (Slot2Mod4_D5 to Slot15Mod4_J5 Signal Layer7) Layer7 

Total length: 24” (50cm + 2 Line Cards, each 5cm) 

AIRMAX 

Demo 

Backplane 

Nelco 4000-6 

Board 

Thickness 

xxxxx 

Total 

Number of 

Layers 

Number of 

Signal Layers 

Back drilling 

On Selected Links 

20 7 

xxxxx 


14” Link with 8db Amplifier 

after FIR Filter 


Measurement results : 14” Link 

with FIR filter + amplifier (single-ended drive) 

25 GB/s 

PRBS 

Source 

Precoder/ 

2-tap FIR 

FIR Filter: 9.4dB, 60ps 

Ampl. Ampl. 

= 920mV pp 

8dB 

Backplane 

Backplane output 

Ampl. Ampl. 

= 460mV pp (eye open. 85mV) 


Measurement results : 14” Link 

with FIR filter + amplifier (single ended drive) 

DuoBinary Decoder outputs shown with demuxed NRZ data 


•BER BER @ PRBS 2 7-1 1 , 2 15 15-1 1 < 10 -13 


13 * 


S21 – single-ended pulse response 14”(35cm) 

Link 

Pulse Response [dB] 

0 

-5 

-10 

-15 

-20 

-25 

-30 

FCI Airmax 14''/35cm link 

w/o FIR filter 

w/ 2-tap FIR 

(65ps, -8.0dB) 

-35 

-3 -2 -1 0 1 2 3 4 5 6 7 8 9 10 

Relative Time [UI @ 25 Gb/s] 


S21 – single-ended pulse response 24”(60cm) 

Link 

Pulse Response [dB] 

0 

-5 

-10 

-15 

-20 

-25 

-30 

FCI Airmax 24''/60cm link 

w/o FIR filter 

w/ 2-tap FIR 

(55ps, -4.8dB) 

-35 

-3 -2 -1 0 1 2 3 4 5 6 7 8 9 10 

Relative Time [UI @ 25 Gb/s]

Bell Labs, Lucent Technologies - Fci.com

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