Paris, October 15, 2008
Data transmission characterization
with underwater copper link
F. Gensolen
CPPM electronics group
Summary
Objective:
>> study the behavior and performances of the state of the art underwater
copper cables and connectors for high speed data transmission (gigabit),
>> characterize both on the table and under pressure (in situ).
Actions :
>> Define the state of the art underwater copper links (including connectors)
>> Build the setups to characterize these copper links :
1. Impedance profile along the link (cable + connectors) + average impedance
2. S-Parameters
4. Real data transmission test
5. Characterization of the data transmission (BER, eye diagram, jitter)
2
Copper link state of the art
MacArtney Ethernet Instrumentation cable (Seacon unavailable)
1 bar
200 bar
600 bar
3
MacArtney P-31000 cable specs
Not state of the art cable but a good opportunity to start tests
4
Impedance measurements
Instrument and setup
One important parameter to transmit electrical data correctly is the impedance.
We have measured the impedance profile along the connection (including
connectors and cable) during a pressure cycle from 1 to 310 bar.
The setup has been installed at Ifremer Brest (France).
Signal integrity analyzer
(Time domain reflectometry)
AGILENT
86100C Infinium
Profil d'impédance câble P-31000 à 50 bar
400
350
300
Tensiion (mV)
250
200
50 bar
150
100
50
0
-200
0
200
400
600
800
1000
Container with pressurized water
P-31000 cable
-50
Temps (ns)
Antares like connectors
5
Impedance profile
Results for a first pressure cycle from 1 to 310 bar
As the cable length remains the same during
the experiment, it shows that the propagation
time depends on the pressure !..
6
Average
impedance variations
Evolution de l'impédance du câble P-31000 en pression (310 bar)
Results for a first pressure cycle from 1 to 310 bar (1hour@310 bar)
140
1201; 116,8
50; 99,33
100
100; 92,54
Impedance (Ohms)
1; 98,86
150; 85,985
80
50; 83,245
100; 80,34
150; 78,92
200; 83,33
200; 78,775
250; 80,72
250; 78,375
310; 79,125
310; 78,13
60
The cable impedance changes with pressure !..
40
20
0
0
50
100
150
200
Pressure (bar)
250
300
350
7
S-parameters
Setup
Important insights into the cable behavior can be achieved through frequency
domain analysis in addition to a characterization in the time domain.
Signal integrity analyzer
(Time domain reflectometry)
P-31000 cable
AGILENT
86100C Infinium
Profil d'impédance câble P-31000 à 50 bar
400
350
300
Tensiion (mV)
250
200
50 bar
150
100
50
0
-200
0
200
400
600
800
1000
-50
Temps (ns)
8
S-parameters
First measurements up to 100 MHz
9
Data transmission test
Setup
In order to characterize the data transmission over this cable and connectors, we
have carried out a real data transmission using :
>> TI board based on TLK2501 serdes as a pseudo-random generator with a
BIST test mode (from 600 Mbps up to 2.5 Gbps)
>> NS DriveCable board with buffer and equalizer (150 Mbps up to 1.5 Gbps).
Oscilloscope
or Digital communication analyzer
Profil d'impédance câble P-31000 à 50 bar
400
350
300
Tensiion (mV)
250
200
50 bar
Digital pattern generator
TEKTRONICS
Oscilloscope
HP-81110
150
100
50
0
-200
0
200
400
600
800
1000
-50
Temps (ns)
Clock
P-31000
Ethernet cable
Data transmission
validation bit
CML signals
TLK2501
LVDS signals
LVDS signals
DriveCable
Equalizer
Buffer
10
Data transmission test
Specifications of critical components (buffer and equalizer)
Buffer
(DS15BA101)
Equalizer (DS15EA101)
142
198
Transition time low >> high
typ / max (ps)
120 / 220
100 / 220
Transition time high >> low
typ / max (ps)
120 / 220
100 / 220
Total jitter @1.5 Gbps (typ)
26 ps
0.25 UI = 166 ps (cat 5e, 25m)
Power @1.25 Gbps (mW)
Timing
Maximum cable loss
35 dB @ 750 MHz
11
Data transmission test
Setup
12
Data transmission test
Data transmission OK @ 800 Mbps with 50 m of P-31000 cable
TEKTRONICS
Oscilloscope
Profil d'impédance câble P-31000 à 50 bar
400
350
300
Tensiion (mV)
250
200
HP-81110
50 bar
150
100
50
0
-200
0
200
400
600
800
1000
-50
Temps (ns)
Clock
TLK2501
DriveCable
Equalizer
Buffer
13
Data transmission characterization
Setup
In order to have an indication of the performance margin of the data
transmission (bit error rate, total jitter, eye opening..) we use the Lecroy
SDA11000 serial data analyser to characterize signals coming out of the cable.
The setup includes :
>> TI board based on TLK2501 serdes as a pseudo-random generator (from
600 Mbps up to 2.5 Gbps)
>> NS DriveCable board with buffer and equalizer (150 Mbps up to 1.5 Gbps)
>> LeCroy SDA11000 serial data analyzer.
Digital pattern generator
Buffer
HP-81110
Serial data analyzer
Clock
DriveCable
LeCroy
SDA11000
TLK2501
Equalizer
14
Data transmission characterization
Example of results @2 Gbps with standard coaxial cable
Eye diagram
Jitter amplitude vs. time
Jitter dispersion
BER (bathtub curve)
15
Summary of measurements
Measurements for copper link characterization :
Physical
modeling
for simulations
Data
transmission
characterization
1>> Impedance profile along the underwater link (cable + connectors)
and average impedance of the cable
2>> S-Parameters
3>> Real data transmission tests
4>> Characterization of the data transmission (BER, eye diagram, jitter)
16
Conclusions
1>> MacArtney Instrumentation cable with connectors is the state of the art
copper link available
>> purchased and waiting for them (December)
2>> First pressure measurements on the P-31000 MacArtney underwater cat 5
copper cable showed that characteristics changed with pressure
3>> All the electronic and instrumental setups are ready for a complete
characterization of the links, both on the table and in hyperbaric tank (January).
17