100 Gb/s Serial Transmission over Copper using Duo-binary Signaling

100 Gb/s Serial Transmission over Copper

using Duo-binary Signaling

Timothy De Keulenaer, (Ghent University)

Ramses Pierco, (Ghent University)

Jan De Geest, (Amphenol FCI)

Joris Van Kerrebrouck (Ghent University), Timothy De Keulenaer (Ghent University)

Jan De Geest (Amphenol FCI), Ramses Pierco (Ghent University), Renato Vaernewyck (Ghent University)

Arno Vyncke (Ghent University), Michael Fogg (Amphenol FCI), Madhumita Rengarajan (Amphenol FCI)

Guy Torfs (Ghent University), Johan Bauwelinck (Ghent University)

SPEAKERS

Timothy De KeulenaerPostdoctoral researcher, Ghent University

[email protected]

www.intec.ugent.be/design/bifast

Ramses PiercoPostdoctoral researcher, Ghent University

[email protected]


mailto:[email protected]

mailto:[email protected]

Introduction

Motivation:

NRZ and PAM4 adopted for 50 Gb/s and 56 Gb/s by IEEE P802.3bs and OIF CEI-56G-XSR/VSR/MR

400 GbE = 8 lanes at 50 Gb/s

Preferred solution: 4 lanes at 100 Gb/s

No solution at this time

Feasibility and advantages of using Duo-binary for 100 Gb/s serial communication

Introduction

Presentation overview:

Quick recap ( Duo-binary signaling )

Signaling comparison ( Nyquist, channel loss, jitter )

Transmission medium ( OIF channels, 100 Gb/s cable channels )

Practical considerations ( Implementation, power consumption, CDR )

Measurement results

Introduction






Measurement results

Quick recap: Duo-binary signaling

Duo-binary VS NRZ:

One Duo-binary symbol =

combination of current and

previous NRZ bit (1 + z-1)

Symbols: +1 (1,1), 0 (0,1 or

1,0) and -1 (0,0)

Duo-binary symbol rate =

NRZ bit rate

+1 never followed by -1

(due to 1 + z-1)

Bandwidth is reduced

Quick recap: Duo-binary signaling

Duo-binary creation:

Create Duo-binary at the

transmitter

Create Duo-binary at the

receiver by means of the FFE

shaping + channel characteristic

(NRZ transmitter)

Easy transmitter

Part of the channel loss doesn’t

need to be compensated ( is

used to create Duo-binary )

Introduction






Measurement results

Signaling comparison: Nyquist frequency

Nyquist frequency:

Used to compare the bandwidth

needed by different modulations

Theoretically: Minimum frequency

for which no ISI occurs

NRZ 1/(2Ts)

PAM4 1/(4Ts)

Duo-binary ?

Signaling comparison: Nyquist frequency

Duo-binary Nyquist frequency:

1/2Ts frequency needed for no

ISI but can be infinitely small

Second largest frequency in

signal = 1/(3Ts)

Eye height = ¾ of Nyquist

frequency signal swing

Signaling comparison: Channel loss

Channel loss at Nyquist determines eye height at the Rx

Lower Nyquist frequency

From a certain amount of channel loss the eye-height at

the receiver will be bigger

PAM4 has 9.54dB penalty compared to NRZ (eye height

divided by Nyquist frequency amplitude)

DB has 2.5dB penalty compared to NRZ

Possible to calculate for a certain data rate the amount of

channel loss for which: DB is better than NRZ, PAM4 is

better than NRZ, PAM4 is better than DB

Data rate 50 Gb/s 100 Gb/s

NRZ DB 0.30

dB/GHz

0.15

dB/GHz

NRZ PAM4 0.76

dB/GHz

0.38

dB/GHz

DB PAM4 1.69

dB/GHz

0.84

dB/GHz


Channel loss at Nyquist method

only correct if Duo-binary created at

transmitter

Eye-height calculation at

receiver based on equalization

transfer function being the

inverse of channel transfer

function.

Not true if Duo-binary created

with equalizer and channel


Real-life system: Eye-height limited by possible amplitude at transmitter

Calculate ideal channel response up to the Tx output (equalizer at the Tx) for NRZ, DB and PAM4 for

a certain amount of channel loss and data-rate DC - value represents eye-height at the receiver

Signaling comparison: Channel loss and CPSD

Previous method correct, but:

No easy calculation formulas

Nyquist of PAM4 based on Nyquist pulses ↔ real-life

consists of rectangular pulses

Equalization up to higher frequencies needed for no ISI

in case of PAM4 (Duo-binary equalized up to 1/2Ts)

Cumulative power spectral density (CPSD) determines

amount of ISI

Higher CPSD lower ISI ( 1/4Ts = 81.5%CPSD )

Signaling comparison: Channel loss and CPSD

Ideal modulation format:

Determined by data rate and

channel loss

Determined by CPSD

percentage needed for PAM4

(depends on desired eye width)

50 Gb/s:

23.1 dB @ 12.5 GHz

46.2 dB @ 25 GHz

Signaling comparison: Jitter

Jitter tolerance, dependent on threshold

level

Largest available eye width

DB: 1 Ts (eye height penalty: 41.4%)

PAM4: 1.33 Ts (eye height penalty: 50%)

Threshold midway eye height

DB: 0.67 Ts

PAM4: 1.07 Ts

Introduction






Measurement results

Transmission medium: OIF 56G channels

Ideal modulation format:

For 56 Gb/s: DB will have

largest eye for VSR and MR

For 100 Gb/s: DB will have

largest eye for XSR and VSR,

for MR dependent on channel

and wanted CPSD for PAM4

Transmission medium: Cable channels for 100 Gb/s

Cable channels:

Lengths from 2m onwards

corresponds to OIF MR

For 56 Gb/s: DB will always

result in larger eye height

For 100 Gb/s: Dependent on

PAM4 CPSD, DB or PAM4

will have larger eye height.


Cable channels:

Suppose 1Vpp at

transmitter

Eye height and

SNR at receiver?

Eye height(mV)| SNR (dB)

ExaMax®30 AWG1m

ExaMax®30 AWG2m

ExaMax®30 AWG3m

QSFP30 AWG2m

QSFP26 AWG3m

NRZ 70.16| 35.8

4.85

| 12.6

<1

| <0

3.75

| 10.4

2.02

| 4.98

Duo-binary 169.5| 48.2

22.49

| 30.7

2.33

| 11.0

18.18

| 28.8

10.85

| 24.4

PAM4, 81.5% 88.08| 43.8

23.10

| 32.2

6.10

| 20.6

20.29

| 31.0

14.89

| 28.4

PAM4, 85% 77.93| 42.3

18.07

| 29.6

4.22

| 17.0

15.69

| 28.4

11.49

| 25.5

PAM4, 90% 61.65| 39.7

11.30

| 24.9

2.09

| 10.3

9.59

| 23.5

6.47

| 20.1


Simulation with measured tap response of real-life FFE:

6 taps with 8.9ps spacing

9-bit resolution

Output driver delivering 1Vpp


Cable channels:

Real-life equalizer

Penalty compared

to theory

Eye height(mV)| Penalty

ExaMax®30 AWG1m

ExaMax®30 AWG2m

ExaMax®30 AWG3m

QSFP30 AWG2m

QSFP26 AWG3m

Duo-binary 120| 29.2 %

10

| 55.5 %

<1 9

| 50.5%

<1

PAM4, 81.5% 52| 41.0 %

5

| 78.4 %

<1 <1 <1

PAM4, 85% 54| 30.7 %

9

| 50.2 %

<1 <1 <1

PAM4, 90% 40|35.1 %

6

| 46.9 %

<1 5

| 47.9 %

<1

Transmission medium: ExaMax® 30 AWG 2m

Duo-binary eye 100 Gb/s PAM4 eye 100 Gb/s

Equalized up to 25 GHz

PAM4 eye 100 Gb/s

Equalized up to 27.3 GHz

(CPSD = 85%)


Why is PAM4 so much worse with real-life FFE

than in theory?

The use of rectangular pulses in real-life

Insufficient to equalize up to the Nyquist

frequency of PAM4 for high-loss channels

ISI reduces eye height

Limited dynamic range (number of bits to set tap

value) seems to affect PAM4 more than DB

(ripple in eye height plot)


What about suck-outs?

Simulation with ideal equalizer (rule out effect of limited number of bits), equalized up to 1/2Ts (no ISI)

Variation of suck-out frequency and width

QSFP, 26AWG, 3m


Suck-out at 40 GHz, 30 GHz and 20 GHz, 0.35 GHz wide and 15dB dip






What about jitter?

PAM4 equalized

up to 1/2Ts (min.

effect of ISI)

Channel loss 0.5 dB/GHz 0.75 dB/GHz 1 dB/GHz 1.25dB/GHz

DB: eye-width

/ penalty

8.2 ps

/ 18%

7.85 ps

/ 21.5%

5.7 ps

/ 43%

4.5 ps

/ 55%

PAM4: eye-width

/penalty

9.15 ps

/ 31.4%

8.85 ps

/ 33.6%

4.7 ps

/ 64.7%

/

/ 100%

Introduction






Measurement results

Practical considerations: Implementation

Transmitter and receiver topology:

NRZ transmitter is sufficient (possibly with equalizer)

Pre-coder needed at transmitter: easy implementation by means of flip-flop and XOR

At the receiver: two slicers followed by XOR

Practical considerations: Power consumption

No easy comparison:

Chipset in same technology for all modulation formats signaling across same channel

= only fair comparison

In previous work this led to lower power consumption for Duo-binary*

First estimates of our new chipset = 1W for one 100 Gb/s link (Tx, Rx+CDR and SERDES)

(* J. Lee, M.-S. Chen, H.-D. Wang, IEEE JSSC, vol.43, no.9, pp. 2120-2133, Sept. 2008)

Practical considerations: CDR

Based on signal crossings:

Duo-binary: single signal crossing

Relative easy CDR implementation

PAM4: multitude of signal crossings

Desired crossing needs to be selected

Adds complexity (larger power consumption)

Introduction






Measurement results

Measurement results

Test setups:

Amphenol FCI ExaMAX® backplane daughter cards – 56 Gb/s

Twin-ax cable – 56 Gb/s

Connectorized test boards – 100 Gb/s

Twin-ax cable – 100 Gb/s

Amphenol FCI ExaMAX® backplane setup:

Serializer + Duo-binary transmitter Duo-binary receiver + De-serializerExaMAX ® backplane channel

Measurement results: Amphenol FCI ExaMAX® backplane

Pattern generator

1 x 56 Gb/s

BERT1 x 14 Gb/s

32 dB @ 28 GHz – BER < 1e-12

Measurement results: 56 Gb/s transmission

Measured Duo-binary transmission:

Backplane channels from 13” up to 20”

56 Gb/s – 13” 56 Gb/s – 20”

43 dB @ 28 GHz – BER < 1e-12

Cable cards – Duo-binary over 26AWG Twin-Ax setup:

Specific card for each length (0.5m, 1.5m, 3m, 5m)

Serializer + Duo-binary transmitter Duo-binary receiver + De-serializer

Measurement results: Twin-ax cable 56 Gb/s

FPGA4 x 14 Gb/s

BERT1 x 14 Gb/s



56 Gb/s – 5m ~38dB @ 28G BER < 1e-12 (error free)

Measurement results: Connectorized test boards

Test setup:

100 Gb/s Duo-binary setup

Duo-binary receiver + De-serializer Serializer + Duo-binary transmitterTest channel

Pattern generator

4 x 25 Gb/s

BERT1 x 25 Gb/s

Measured 100 Gb/s Duo-binary eye

Measurement results: 100 Gb/s transmission


Initial channel for verification

Channel loss ≈ 0.3 dB/GHz

BER < 1e-12 (error free)

Cable cards – Duo-binary over 26AWG Twin-Ax setup:

Specific card for each length (0.5m, 1.5m, 3m, 5m)

Serializer + Duo-binary transmitter Duo-binary receiver + De-serializer


FPGA4 x 25 Gb/s

BERT1 x 25 Gb/s



100 Gb/s – 1.5m ~35dB @ 50G BER < 1e-12 (error free)

Conclusions

Duo-binary strongpoints:

Outperforms competition with real-life equalizer

High tolerance to jitter and suck-outs

Limited implementation complexity, low power consumption

Measurement results:

Backplane channel: 56 Gb/s up to 20” error free (no FEC, 43dB @ 28GHz)

Twin-ax cable (26AWG):

56 Gb/s up to 5m error free (no FEC), 8m feasible with FEC

100 Gb/s up to 1.5m error free (no FEC), 3m feasible with FEC

44

MORE INFORMATION


Visit us at the booth of

Amphenol FCI 533

[email protected]

[email protected]

http://www.intec.ugent.be/design/bifast

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100 Gb/s Serial Transmission over Copper using Duo-binary Signaling