DATA & DEVICES

An Initial Investigation of a Serial “100”Gbps PAM4 VSR Electrical Channel

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Nathan TracyTE ConnectivityMay 24, 2017

DATA COMMUNICATIONS

Agenda

• Transmission over copper• Channel description• Existing 25G channel review• Setting 100G targets• 100G VSR channels• Conclusions

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DATA COMMUNICATIONS

Higher speed copper transmission

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What are the limits of copper?• Higher speed copper was predicted to be dead

a decade ago– but this has also been the case for the last 30 years

• Copper keeps on pushing the frequency limits• Copper vs optical – gap is closing as speeds

increase• Although optics offer reach and density,

electrical still offers lower cost and power • Equalization technology and modulation

techniques continue to be improved• PAM4, ENRZ, Duobinary, etc.

• The economics at stake are huge, “Do you really want to bet against copper?”

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Channels Considered for this Discussion

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VSR - Connecting Chips to Modules - Typical Reach up to 10”

4-10”, PWB trace

Connector with footprint0.7-1.5”, PWB trace

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Reminder of 25 & 50G Channel Requirements

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50GBaud PAM4 [IEEE Draft 802.3bs]56GBaud PAM4 [OIF Draft oif2014.230.09]56Gbps NRZ, 20dB [OIF Draft oif2016.101.00]56Gbps NRZ, 13dB [OIF Draft oif2016.101.00]

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25Gbps NRZ [IEEE Std. 802.3bm]28Gbps NRZ [OIF CEI-28G-VSR]

VSR Channel IL Limits

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Assumptions to Determine 100G Target• Used 25G (published) and 50G (in development) OIF and IEEE industry

standards as starting point

• Based on the shift towards PAM4 with the transition from 25G to 50G we can assume 100G will likely be PAM4

• Other encoding schemes were not considered but new emerging methods could enable next generation high speed links.

• For 100G the actual data rate will likely be 112Gbps with a Nyquist frequency around 28GHz (PAM4)

• The bandwidth of interest is assumed to be 10MHz – 56GHz

• The Insertion Loss/Return Loss requirements were extrapolated using a combination of,

• Historical trends in data rate leaps, using current 50G targets as reference• Successful demonstrations of actual channels at 50G (PAM4 and NRZ)

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Very Short Reach (Chip to Module) Limits

25Gbps NRZ [IEEE Std. 802.3bm]28Gbps NRZ [OIF CEI-28G-VSR]50GBaud PAM4 [IEEE Draft 802.3bs]56GBaud PAM4 [OIF Draft oif2014.230.06]56Gbps NRZ, 20dB [OIF Draft oif2016.101.00]56Gbps NRZ, 13dB [OIF Draft oif2016.101.00]112G PAM4 [GUESS]

Target 17.5dB@ 28GHz

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Existing VSR Channel vs New Limits

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10”, PWB traceConnector with footprint 1” PWB trace

4”, PWB trace

Improved Connector with footprint

0.4” PWB trace 2”, PWB trace

Board mounted cable connector

18” of 33AWG or 23” of 30 AWG cable

Improved Connector with footprint

Two Possible Paths for Improvement

Reduce Channel Length Use Lower Loss Channel

~10 dB gap

N4000-13SI PWB material

0.4” PWB trace

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- 3.5mm thick- 8mil stub- Long via barrel

Shorter VSR Channels

Conclusions:• Passes up to the Nyquist frequency but may be impractical lengths • Footprint is critical. FP causes significant degradation beyond 33GHz

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4”, PWB trace0.7” PWB trace

Megtron6EM888

Improved Connector with footprint

Meg6 provides 2” of additionaltrace on DC

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Using Cables to Extend Channel Length

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2”, PWB trace

Board mounted cable connector

18” of 33 AWG cableOR

23” of 30 AWG Cable

Improved Connector with footprint

0.7” PWB trace

Conclusions:• Passes up to the Nyquist frequency with margin• Utilizing cable provides extended reach and flexibility

Megtron6, Typical FPMegtron6, Short FP

- 3.5mm thick- 8mil stub- Long via barrel

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PCB vs. Cable Consistency Measurements

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14.00 GH

z

12.50 GH

z

11.00 GH

z

9.50

0 GH

z

8.00

0 GH

z

6.50

0 GH

z

5.00

0 GH

z

3.50

0 GH

z

2.00

0 GH

z

500.0 MHz

0

-2

-4

-6

-8

-10

FREQ

dB

B2_T0

B2_EOL

Variable

PCB T0 vs. EOL VarianceSDD21- PCB B2

1250011000950080006500500035002000500

0

-2

-4

-6

-8

-10

Freq (MHz)

dB

Pair 14-15_cable1_1

Pair 14-15_cable1_after

Variable

Whisper T0 vs. EOL VarianceSDD21 Pair 14-15

T0 vs EoL: Temperature/Humidity cycling per EIA-364-31 Method III200mm PWB Megtron 6 traces vs. 500mm twinax cable assemblies

0.25dB @14 GHz Change No Change

95

96

97

98

99

100

101

102

103

104

105

4.7E-08 4.705E-08 4.71E-08 4.715E-08 4.72E-08 4.725E-08 4.73E-08 4.735E-08 4.74E-08 4.745E-08 4.75E-08

PCB Trace Differential Impedance

95

96

97

98

99

100

101

102

103

104

105

4.77E-08 4.775E-08 4.78E-08 4.785E-08 4.79E-08 4.795E-08 4.8E-08 4.805E-08 4.81E-08 4.815E-08 4.82E-08

Bulk Cable DIfferential Impedance

5% PWB Impedance Tolerance 2% Cable Impedance Tolerance

IL V

aria

nce

Dur

ing

Tem

p/H

umid

ityTy

pica

l Im

peda

nce

Varia

nce

200mm FR4 PWB Material 500mm, 30 AWG Cable

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PCB & Cable Consistency Measurements

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27” PWB Megtron 6 traces vs. 1m twinax cable assemblies

-50

-45

-40

-35

-30

-25

-20

-15

-10

-5

0

0 2 4 6 8 10 12 14 16 18 20

Mag

nitu

de (d

B)

Frequency (GHz)

SCD21- SDD21All 3 Cables

SCD-SDD (dB) A2A3_C1 SCD-SDD (dB) B2B3_C1 SCD-SDD (dB) C2C3_C1SCD-SDD (dB) D2D3_C1 SCD-SDD (dB) H2H3_C1 SCD-SDD (dB) J2J3_C1SCD-SDD (dB) K2K3_C1 SCD-SDD (dB) L2L3_C1 SCD-SDD (dB) A2A3_C2SCD-SDD (dB) B2B3_C2 SCD-SDD (dB) C2C3_C2 SCD-SDD (dB) D2D3_C2SCD-SDD (dB) H2H3_C2 SCD-SDD (dB) J2J3_C2 SCD-SDD (dB) K2K3_C2

Mode Conversion (Skew) SCD21-SDD21 Measurements

~2-4ps of skew ~6-8ps of skew

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02 03 05 06

37 36 33 34

- 3.5mm thick- 8mil stub- Long via barrel

Typical Noise vs. IL in a Shorter VSR Channel

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4”, PWB trace0.7” PWB trace

Improved Connector with footprint

Short FPTypical FP

- Micro-via- No stub- Short via barrel

Typical FP Short FP

>20dB SNR @ 28 GHz

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Ideal mating zone & short footprintRealistic mating zone & short footprintIdeal mating zone & typical footprint (thick board with 8mil stub)Realistic mating zone & typical footprint (thick board with 8mil stub)

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4”, PWB trace0.7” PWB trace

VSR Sensitivity to Connector Design

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VSR Sensitivity to Cable Termination Variance

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Cable termination Impedance varied +/- 10%

Nominal+/-10% Impedance

- Excess solder paste- Inaccurate cable placement - Stripping of signal insulation and shield- Manufacturing control is critical

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112 Gbps COBO Sliver Demo at DesignCon 2017

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TE’s COBO test board with Macom’s serial 112Gbps silicon

10dB channel (7dB COBO channel plus 3 dB Macom test board)

COBO Module Connector

Macom100Gbps PAM4

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Conclusions

Don’t bet against 112Gbps copper for VSR channels100G VSR channels are possible (multiple public demos)New lower loss techniques should be implementedManufacturing consistency will be even more criticalEffects of footprints becoming as critical as the connector itselfNeed better definition of silicon and package requirements

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