Initial Investigation of 112Gbps VSR Channelgrouper.ieee.org/groups/802/3/ad_hoc/ngrates/... ·...
Transcript of Initial Investigation of 112Gbps VSR Channelgrouper.ieee.org/groups/802/3/ad_hoc/ngrates/... ·...
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?”
DATA COMMUNICATIONS
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
DATA COMMUNICATIONS
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
DATA COMMUNICATIONS
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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DATA COMMUNICATIONS
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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DATA COMMUNICATIONS
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
DATA COMMUNICATIONS
- 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
DATA COMMUNICATIONS
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
DATA COMMUNICATIONS
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
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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
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102
103
104
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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
DATA COMMUNICATIONS
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
DATA COMMUNICATIONS
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
DATA COMMUNICATIONS
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
DATA COMMUNICATIONS
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
DATA COMMUNICATIONS
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
DATA COMMUNICATIONS
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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