Quake Technologies, 10GBASE-CX4 Crosstalk Impact on System Performance Simulation
10GBASE-CX4 Crosstalk Impact on System Performance Simulation
1. Outline
• Initial Considerations
• Simulation Environment
• MDNEXT and MDELFEXT Models, Frequency Response
• Crosstalk Worst Case Analysis
• Worst case 15 m cable assembly simulation results
- Simulation environment for crosstalk impact
- Vertical eye reduction due to crosstalk
- Jitter increase due to crosstalk
• Worst case 0 m cable assembly simulation results
- Simulation environment for crosstalk impact
- Vertical eye reduction due to crosstalk
- Jitter increase due to crosstalk
• Driver Output Level Variation Impact
• Conclusions and Recommendations
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2. Initial Considerations
- For drivers and input comparators, including package, models for the actual blocks will be used.
- Two pattern generators will be used for simulation, PRBS 27-1 and 1010.. continuous signal.
- For Near-End (NEXT) crosstalk, a model based on the power sum loss between a receive channel
and the four transmit channels, MDNEXT Eq. 54.6, will be used.
- For Far-End (FEXT) crosstalk, a model based on the power sum loss between a duplex channel
and the three adjacent disturbers, MDELFEXT Eq. 54.9, will be used.
- The transmitter jitter, maximum 0.35 UI_pp, was not included in the simulation.
- The random jitter added by the simulation environment will be very small, such that the random
jitter at the receiver input will be equal to the transmitter random jitter.
- The total deterministic jitter, at the receiver input, will be the sum of the transmitter deterministic
jitter and the jitter introduced by the simulation environment.
- The additional degradations due to impedance variation was not included.
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3. Simulation Environment
Figure 1. Simulation Models
PRBS
27-1
Generator
Mask
Signal
2
Package
2
Model
Generator Upper/Lower
(Clause 54)
Driver
500/240
(nominal)
2
2
(Quake XAUI/10G IC)
Connector 2
Model
(Clause 54)
2
2
2
2
2” FR4 TL 2
Model
Cable
(XFP 3.0)
2
Model
(15 m)
(Clause 54)
(1.2 dB package, FR4 TL, and connector added)
500mV
(550/450)
240mV
(264/216)
2
MDNEXT
Model
240mV
2
(Clause 54)
500mV
Pulse Width
(320ps)
110 ps > tr,tf > 60 ps
2
MDELFEXT
Model
2
(Clause 54)
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4. MDNEXT and MDELFEXT Models, Frequency Response
Figure 2. Frequency Response
MDELFEXT
MDNEXT
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5. Crosstalk Worst Case Analysis
Figure 3. MDNEXT Disturber PRBS (27-1) and 1010.. Pattern Comparison
..10100100..
1010.. Pattern
PRBS (27-1) Pattern
Worst case disturber amplitude, using PRBS pattern, is the same as the disturber generated using a 1010.. pattern. The advantage of the 1010.. pattern is that the disturber is active every bit time.
Using 1010.. pattern, will generate the worst possible case for every bit. Using a PRBS pattern, the probability of
a worst case disturber, for a given bit, is much lower.
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Figure 4. MDELFEXT Disturber PRBS (27-1) and 1010.. Pattern Comparison (0 m cable)
..10100100..
1010.. Pattern
PRBS (27-1) Pattern
Worst case disturber amplitude, using PRBS pattern, is the same as the disturber generated using a 1010.. pattern.
The advantage of the 1010.. pattern is that the disturber is active every bit time.
Using 1010.. pattern, will generate the worst possible case for every bit. Using a PRBS pattern, the probability of a
worst case disturber, for a given bit, is much lower.
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Figure 5. MDELFEXT Disturber PRBS (27-1) and 1010.. Pattern Comparison (15 m cable)
1010.. Pattern
PRBS (27-1) Pattern
Worst case disturber amplitude, using PRBS pattern, is the same as the disturber generated using a 1010.. pattern.
The advantage of the 1010.. pattern is that the disturber is active every bit time.
Using 1010.. pattern, will generate the worst possible case for every bit. Using a PRBS pattern, the probability of a
worst case disturber, for a given bit, is much lower.
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Crosstalk Worst Case Definition
• case 1: Vertical Eye Opening Reduction due to Crosstalk
- MDNEXT and MDELFEXT (101010.. pattern) signals are aligned in phase
- MDNEXT and MDELFEXT peak signal aligned with the received eye centre
MDELFEXT
MDNEXT
• case2: Jitter Increase due to Crosstalk
- MDNEXT and MDELFEXT (101010.. pattern) signals are aligned in phase
- MDNEXT and MDELFEXT peak signal aligned with the received eye crossings
MDNEXT
crossing
MDELFEXT
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Figure 6. Simulation Environment for Crosstalk Impact (15 m cable assembly)
TP2
TP3
TP1
PRBS
27-1
Generator
2
Driver
2
500/240
(nominal)
2” FR4 TL 2
Model
Cable
Connector
2
Model
Model
(15 m)
(including package)
010101
2
Generator
Driver
2
500/240
(nominal)
TP4
2” FR4 TL 2
MDNEXT
2
Model
Model
Generator
2
Driver
2
2
500/240
(nominal)
2” FR4 TL 2
Model
MDELFEXT
2” FR4 TL
Model
(including package)
010101
2
TP5
2
Model
2
TP6
Input
Comp. 2
and
Equalizer
(including package)
Cable
Connector
Model
Model
(15 m)
(including package)
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Figure 7. Vertical Eye Opening Reduction due to Crosstalk (worst case 15 m cable)
TP5
No crosstalk present, 0.1 UI_pp added
Vertical eye opening, 142 mV_pp
TP5
Crosstalk present, 0.15 UI_pp added
Vertical eye opening, 50 mV_pp
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Figure 8. Jitter Increase due to Crosstalk (worst case 15 m cable, equal transmit levels)
TP5
No crosstalk present, 0.1 UI_pp added
TP5
Crosstalk present, 0.35 UI_pp added
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Figure 9. Jitter Increase and Vertical Eye Opening Reduction due to Crosstalk (worst case 15 m cable)
TP5
TP5
No crosstalk present, 0.1 UI_pp jitter added
Vertical eye opening, 143 mV_pp
Crosstalk present (mid point between crossing and centre)
0.35 UI_pp added jitter
Vertical eye opening, 128 mV_pp
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Quake Technologies, 10GBASE-CX4 Crosstalk Impact on System Performance Simulation
Figure 10. Simulation Environment for Crosstalk Impact (0 m cable assembly)
TP2 TP3
TP1
PRBS
27-1
Generator
2
Driver
500/240
500/240
(nominal)
2
Connector Connector
2” FR4 TL 2
Model
Model
Model
(including package)
010101
2
Generator
Driver
2
500/240
(nominal)
Generator
2
Driver
2” FR4 TL 2
Model
2
500/240
(nominal)
TP5
TP4
MDNEXT
2
2
2” FR4 TL
Model
Model
(including package)
010101
2
2
TP6
Input
Comp. 2
and
Equalizer
(including package)
2” FR4 TL 2
Model
MDELFEXT
2
Model
(including package)
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Quake Technologies, 10GBASE-CX4 Crosstalk Impact on System Performance Simulation
Figure 11. Vertical Eye Opening Reduction due to Crosstalk (worst case 0 m cable)
TP5
Eye opening reduced to 210 mVpp (differential)
TP5
Eye opening (no crosstalk) 440 mVpp (differential)
Small (1.3 ps) increase in jitter.
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Figure 12. Jitter Increase due to Crosstalk (worst case 0 m cable)
TP5
TP5
No crosstalk present, 0.06 UI_pp added
Crosstalk present, 0.14 UI_pp added jitter
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6. Driver Output Level Variation Impact
- 802.3ak D4.0 specification 800 to 1600 mVpp (1200 mV +/- 33%) will not
work.
- Restrict the output level variation to +/- 10%.
- Include output level variation in worst case definition:
- assume victim driver output level - 10%,
- assume all other drivers (NEXT and FEXT) + 10%,
- simulate worst case crosstalk impact (jitter and vertical eye closure)
for +/- 10% output level variation,
- include receiver equalizer contribution.
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Figure 13. Worst Case (1000 mV_pp +/- 10%) Crosstalk Impact
TP5
Worst case vertical eye closure
Vertical eye opening, 26.69 mV_pp
TP5
Worst case horizontal eye closure
119 ps (0.37 UI_pp) added jitter
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Figure 14. Worst Case (1000 mV_pp +/- 10%) Received Vertical Eye Opening Assuming First Order Equalizer
TP6
TP6
Worst case vertical eye closure, equal levels
Vertical eye opening, 400 mV_pp, 0.14 UI_pp
jitter added.
Worst case vertical eye closure, worst case levels
Vertical eye opening 320 mV_pp, 0.16 UI_pp added jitter
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Figure 15. Worst Case (1000 mV_pp +/- 10%) Received Horizontal Eye Opening Assuming First Order Equalizer
TP6
Worst case horizontal eye closure, equal levels
Vertical eye opening, 460 mV_pp, 0.34 UI_pp
jitter added.
TP6
Worst case horizontal eye closure, worst case levels
Vertical eye opening 450 mV_pp, 0.38 UI_pp added jitter
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7. Conclusions and Recommendations
- The receiver input eye degradation (vertical and horizontal eye opening) will increase with the
cable length.
- The assumption, that the receive signal and MDELFEXT disturber are coherent, is valid.
- The main contributor to signal degradation for long cables is MDNEXT.
- Driver differential peak amplitude at TP2 (Table 54-6) allows for +/- 33% and needs to be changed.
For driver differential peak amplitude1000 mV_pp +/- 10%, the worst case simulation results are:
- minimum differential vertical eye opening at TP5 is 26.69 mV_pp and can be improved
using a first order equalizer (TP6),
- worst case total jitter contribution of the cable assembly (TP4) is 0.37 UI_pp (Table 54-9
allows for 0.18 UI_pp), the equalizer (TP6) may reduce the jitter by a small amount (nominal
0.1 UI_pp, worst case 0.05 UI_pp).
- We recommend the following changes:
- Driver differential peak amplitude at TP2 (Table 54-6), maximum 1000 mV_pp and minimum
800 mV_pp,
- Cable assembly total jitter contribution at TP4 (Table 54-9), maximum 0.37 UI_pp,
- Total jitter at TP4 (Table 54-9), maximum 0.84 UI_pp.
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