evaluation of multi-gbps optical transceivers for use in future hep experiments
DESCRIPTION
Evaluation of Multi-Gbps Optical Transceivers for Use in Future HEP Experiments. Luis Amaral CERN – PH/ESE/BE – Opto 16/09/2008. Outline. Introduction Optical Links Upgrade for SLHC Project Organization Commercial Optical Transceivers Overview Devices Under Test - PowerPoint PPT PresentationTRANSCRIPT
Evaluation of Multi-Gbps Optical Transceivers for Use in Future
HEP Experiments
Luis AmaralCERN – PH/ESE/BE – Opto
16/09/2008
Outline• Introduction
– Optical Links Upgrade for SLHC– Project Organization
• Commercial Optical Transceivers– Overview– Devices Under Test
• Performance Evaluation of Commercial Optical Transceivers– Setups and Procedures– Performance metrics– Specification Proposal for Operation at 5Gbps
• Analysis of the Data and Results– Figure of Merit– Results of the Devices Under Test
• Summary
TWEPP 2008
Optical Link Upgrade for LHC• The future SLHC upgrade is expected to increase the LHC luminosity by an
order of magnitude. This implies:– More data to be transmitted;
• Assuming more complex DAQ/TTC/SC systems.
– Higher radiation doses.• The optical links are also required to have low power dissipation and to
reduce the mass inside the detector.• The solution is to increase the bandwidth of each individual link.
– The links will be required to:• Run at multi-Gbps speeds;• Have better radiation tolerance;• Operate at low temperatures and in strong magnetic field;• Be easy to install and operate.
• The goal is to come up with a common solution that offers:– System architectures;– Basic building blocks.
TWEPP 2008
GBTXPD
LDTRx FPGA
●●
●●
●●
On-DetectorCustom Electronics and Packaging
Radiation Hard
Off-DetectorCommercial Off-The-Shelf (COTS)
Custom Protocol
GBT GBTVersatile Link
Timing and TriggerDAQ
Slow Control
Timing and TriggerDAQ
Slow Control
TIA
LDD
Radiation-Hard Optical Link for Experiments
Project Organization
TWEPP 2008
Project Organization
• The GBT project covers the ASIC design, verification and packaging.
• The Versatile Link project covers system architectures and the components.
• One of the main F.E. components is a Versatile Transceiver (VTRx), which results from the customization of a commercial transceiver (TRx).
GBTSpokesperson:
P. Moreira
WP 1System
WP 2Components
WP 1.1 - P2P, SMU, J. Ye
WP 1.2 - PON WP 1.3 - Mixed
WP 2.1 - F.E. Components,
CERN, J. Troska
WP 2.2 - B.E. Components
WP 2.3 - Passive Components,
Oxford, C. Issever
Versatile LinkSpokesperson:
F. Vasey
TWEPP 2008
GBTXPD
LDTRx FPGA
●●
●●
●●
On-DetectorCustom Electronics and Packaging
Radiation Hard
Off-DetectorCommercial Off-The-Shelf (COTS)
Custom Protocol
GBT GBTVersatile Link
Timing and TriggerDAQ
Slow Control
Timing and TriggerDAQ
Slow Control
TIA
LDD
Radiation-Hard Optical Link for Experiments
Commercial Transceivers Overview
1211109876543210Gbps
1
0
OC3/STM1OC12/STM4
1GFCGbE
2GFCOC48/STM16
4GFCGBT (4.8Gbps)
8GFC10GBASE-R
10GBASE-W & OC192/STM64
10GFCOC192/STM64 + FEC
10GFC + FEC10GE + FEC
SFP+XFPSFP
• The goal is the VTRx customization of a commercial TRx.
• There are several families of commercial optical TRxs to target the Telecom and Datacom standards.
• The GBT project specifies a single lane running at 4.8Gbps which is not a standard.
TWEPP 2008
Commercial Transceivers Overview
1211109876543210Gbps
1
0
OC3/STM1OC12/STM4
1GFCGbE
2GFCOC48/STM16
4GFCGBT (4.8Gbps)
8GFC10GBASE-R
10GBASE-W & OC192/STM64
10GFCOC192/STM64 + FEC
10GFC + FEC10GE + FEC
• The goal is the VTRx customization of a commercial TRx.
• There are several families of commercial optical TRxs to target the Telecom and Datacom standards.
• The GBT project specifies a single lane running at 4.8Gbps which is not a standard.
SFP+ TRxs seem to be worthy of our attention.What are they made of?
LA
LDD TOSA
ROSACAGE Controller (back)
SFPs are similar but rated for lower speeds and the XFPs include a clock and data recovery circuit on both Tx and Rx paths.
TWEPP 2008
SFP+XFPSFP
Devices Under TestDevice # TRx Type Wavelength [nm] Max. Bitrate [Gbps] LD/PD type Applications
1 SFP 850 4.25 VCSEL/PIN 1/2/4GFC; 1000BASE-SX 2 SFP 1310 4.25 VCSEL/PIN 1/2/4GFC; 1000BASE-LX10 3 SFP+ 850 10.5 VCSEL/PIN 2/4/8/10GFC; 10GBASE-SR 4 SFP+ 850 10.5 VCSEL/PIN 2/4/8/10GFC; 10GBASE-SR 5 SFP+ 1310 10.5 DFB/PIN 2/4/8/10GFC, 10GBASE-LR 6 SFP+ 1310 10.5 DFB/PIN 2/4/8/10GFC, 10GBASE-LR 7 XFP 1310 10.3 DFB/PIN 10GBASE-LR/LW 8 SFP+ 1310 10 VCSEL/PIN Prototype for 10Gbps over SM fiber 9 SFP+ 1310 10 VCSEL/PIN Prototype for 10Gbps over SM fiber
10 SFP+ 1310 10 VCSEL/PIN Prototype for 10Gbps over SM fiber 11 SFP+ 1310 10 VCSEL/PIN Prototype for 10Gbps over SM fiber 12 SFP+ 1310 10 VCSEL/PIN Prototype for 10Gbps over SM fiber
Testboard
SFP+ module in
side
an assembly ca
ge
• Our evaluation was guided towards the performance at 5Gbps, i.e. slightly faster than what the GBT protocol is targeting (4.8Gbps).
• Some devices are suitable for MM links operating at 850nm and other are suitable for SM links operating at 1310nm.
• Some devices have VCSELs (850 and 1310nm) and other have DFB lasers (1310nm).
TWEPP 2008
Receiver
Transmitter SDA ScopePRBS
SourceClock
Generator PC Automation:Runs through several
bitrates and saves data
Setup A(Tx) Optical Evaluation
PRBS7 Test Pattern Jitter @5Gbps:Tj@1E-12=0.10UI, Dj=0.03UI
20%-80% Rise/Fall Times: 28/27ps
10GHz Optical Sampling Module Without Filtering0.5-12.5GHz PRBS7-PRBS31
2m Optical Fiber
Testboard and DUT
Tx Performance Evaluation – Eye Diagram
TWEPP 2008
Receiver
Transmitter SDA ScopePRBS
SourceClock
Generator PC Automation:Runs through several
bitrates and saves data
Setup A(Tx) Optical Evaluation
PRBS7 Test Pattern Jitter @5Gbps:Tj@1E-12=0.10UI, Dj=0.03UI
20%-80% Rise/Fall Times: 28/27ps
10GHz Optical Sampling Module Without Filtering0.5-12.5GHz PRBS7-PRBS31
2m Optical Fiber
Testboard and DUT
Tx Performance Evaluation – Eye Diagram
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Unit Interval (UI) = 200ps @5Gbps
Jitter Jitter
OMAEyeOpening
Level 1
Level 0
20% V. Center Window
H. Center
Window
Open Level 1
Open Level 0
Time
Op
tica
l Po
wer
Higher # of hitsNo hits above
Higher # of hitsNo hits below
Gaussian tail fitting Gaussian tail fitting
Histogram Histogram
Histogram
Eye diagram
Specification Proposal for 5Gbps Operation# Specification Min Max Unit Note1 OMA 300 uW 2 ER 3 dB 3 Eye closure 60 %4 Rise Time 65 ps 20%-80%5 Fall Time 65 ps 20%-80%
6 Total Jitter 0.25 UI @BER=1E-12, (1)
7 Deterministic Jitter 0.12 UI (1)
(1) The Tx jitter spec. is the 4GFC Tx jitter budget, not including the jitter of the test set-up.
Tx optical output and metrics:
by processing the Tx eye raw data
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d t
o t
he O
MA
Unit Interval (UI) = 200ps @5Gbps
Tx Performance Evaluation – Mask Test• The mask defines an area which the
eye diagram must not cross.• Although based on the 4GFC Tx mask,
the jitter and slope are adjusted to the previous specifications and to the jitter of our test setup.
• The maximum overshoot is 40% to allow laser driver pre-emphasis and because no filtering is being used.
• The green arrows defines the mask margin from 0% to 100%.
Tx Relative Mask(based on the 4GFC spec.)
Specification Proposal for 5Gbps Operation# Specification Min Max Unit Note
8 Tx Mask Margin 0% % (2)
• The mask defines the limits for the overshoot and ringing but cannot be used to test jitter or rise/fall time compliance.
(2) The margins of the full and center mask must be measured as they will be used to compare different devices.
by processing the Tx eye raw data
TWEPP 2008
2m Optical Fiber
Clock Generator
PRBS Source
Optical Attenuator and Power
Meter
Testboard and DUT
2m Optical Fiber
SDA Scope
PRBS7 Test Pattern Jitter @5Gbps (both 850 and 1310nm):Tj@1E-12=0.11UI, Dj=0.04UI
Setup B(Rx) Electrical
Evaluation
850nm/1310nmOptical Tx
20GHz Electrical Sampling Module Without Filtering
0.5-12.5GHz PRBS7-PRBS31Transmitter
Receiver
20%-80% Rise/Fall Times:850nm: 38/46ps, 1310nm: 35/42ps
PC Automation:Runs through several
attenuations (and bitrates) and saves data
Rx Performance Evaluation – Eye and Mask
TWEPP 2008
2m Optical Fiber
Clock Generator
PRBS Source
Optical Attenuator and Power
Meter
Testboard and DUT
2m Optical Fiber
SDA Scope
PRBS7 Test Pattern Jitter @5Gbps (both 850 and 1310nm):Tj@1E-12=0.11UI, Dj=0.04UI
Setup B(Rx) Electrical
Evaluation
850nm/1310nmOptical Tx
20GHz Electrical Sampling Module Without Filtering
0.5-12.5GHz PRBS7-PRBS31Transmitter
Receiver
20%-80% Rise/Fall Times:850nm: 38/46ps, 1310nm: 35/42ps
PC Automation:Runs through several
attenuations (and bitrates) and saves data
-0.3
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0.16 0.840 1
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Unit Interval (UI) = 200ps @5Gbps
Dif
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Ele
ctr
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l A
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[m
V]
Rx Performance Evaluation – Eye and Mask
Specification Proposal for 5Gbps Operation# Specification Min Max Unit Note
9 Total Jitter 0.26 UI @BER=1E-12, (3), (4)
10 Deterministic Jitter 0.11 UI (3), (4)
11 Rx Mask Pass Pass/Fail test,(4)
(3) The Rx jitter spec. is the 4GFC Rx jitter budget , not including the jitter of the test set-up.(4) Measured with an input OMA of 90uW.
Rx Absolute Mask(based on the SFP+ SFI spec. )
Defines the limits for the electrical swing.
TWEPP 2008
2m Optical Fiber
2m Optical Fiber
850nm/1310nmOptical Tx
0.5-6.5GbpsPRBS7-PRBS31 and others
FPGA-Based BER Tester
Clock Generator
Receiver
Transmitter
Setup C(Rx) Sensitivity
Evaluation Testboard and DUT
Optical Attenuator and Power
Meter
PC Automation:Runs through several
OMAs and saves the BER
Rx Performance Evaluation – BER
TWEPP 2008
2m Optical Fiber
2m Optical Fiber
850nm/1310nmOptical Tx
0.5-6.5GbpsPRBS7-PRBS31 and others
FPGA-Based BER Tester
Clock Generator
Receiver
Transmitter
Setup C(Rx) Sensitivity
Evaluation Testboard and DUT
Optical Attenuator and Power
Meter
PC Automation:Runs through several
OMAs and saves the BER
Rx Performance Evaluation – BER
Specification Proposal for 5Gbps Operation# Specification Min Max Unit Note12 Sensitivity 45 uW (5), (6)
10-13
10-12
10-11
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R
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OMA [dBm]
1310nm 850nm
Sensitivity@1E-12
Sensitivity@1E-12
10G Rx10G Rx
Rx BER curves – Two examples
(5) Specified for a BER of 1E-12.(6) The sensitivity is specified as an OMA. The setup reads average power and the OMA is calculated using the Tx ER.
• By measuring the Bit Error Rate (BER) at different OMAs the BER curve is created.
• The Rx sensitivity is defined as the minimum OMA which allows a 1E-12 BER.
TWEPP 2008
Evaluation of the TRx Power Dissipation
Receiver
TransmitterPRBS
SourceClock
GeneratorPC
Automation
2m Optical Fiber
Optical Attenuator and Power
Meter
Setup D(TRx) Power Dissipation 2m Optical
FiberPower Supply
Clean Testboard (no additional electronics)
and DUT
Specification Proposal for 5Gbps Operation# Specification Min Max Unit Note13 Power Dissipation 600 mW (7)
(7) End-of-life power dissipation and across all operating temperatures and all Rx optical input levels.
• To measure the power dissipation we can simply read current being supplied to the host board.
• The setup is to measure the power at different bitrates and Rx optical input levels.
• In reality we measured the non end-of-life power dissipation at room temperature.
Our experience with commercial TRxs tells us that this spec. might be very harsh for non VCSEL-based transmitters.
TWEPP 2008
Analysis of the Data
• The previous test setups generate a very large data set: raw eye diagrams, direct scope measurements, BER curves and measurements of the raw data.
• As we are interested in the TRx performance at 5Gbps we discard all other bitrates and compare the measurements with the specification.
Tx Perform
ance
at 5Gbps
Rx Perform
ance
at 5Gbps
Power
Dissipation
Flag devices non-compliant with
the spec.
• We flag the devices that do not meet the spec. and we have developed a Figure of Merit (FoM) that combines all the performance data into three numbers: for the Tx part (Tx_FoM), for the Rx part (Rx_FoM) and for the power dissipation (Pwr_FoM).
TWEPP 2008
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_Fo
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121110987654321
Figure of Merit1.0
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There is a strong correlation between the performance of the device and the FoM number.
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WorstTx
BetterTx
BestTx
TWEPP 2008
SFP+
10G 13
10VCS
EL #5
SFP+
10G 13
10VCS
EL #4
SFP+
10G 13
10VCS
EL #3
SFP+
10G 13
10VCS
EL #2
SFP+
10G 13
10VCS
EL #1
XFP 1
0G 13
10DFB
SFP+
10G 13
10DFB
#2
SFP+
10G 13
10DFB
#1
SFP+
10G 85
0VCS
EL #2
SFP+
10G 85
0VCS
EL #1
SFP 4
G 1310
VCSEL
SFP 4
G 850V
CSEL
139 171 183
RED=FAILGREEN=PASS
Tx
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TWEPP 2008
Pow
erTx
Rx
• SFP (devices 1 and 2): Tx problems with rise/fall times or jitter. Rx jitter problems. Both and Tx and Rx masks fail.
• SFP+ 850mn VCSEL (devices 3 and 4): Good power dissipation and very good 5Gbps Tx performance. The sensitivity of the PINs at 850nm was found to be around -16dBm. The Rx jitter is good with 90uW of OMA (spec.).
• SFP+ 1310mn DFB (devices 5 and 6): Good 5Gbps Tx performance but high power dissipation. The sensitivity of the PINs at 1310nm was found to be around -19dBm.
• XFP 1310nm DFB (device 7): Great jitter performance but very high power dissipation.
• SFP+ 1310mn VCSEL (devices 8 to 12): Great power dissipation and good 5Gbps Tx performance in most of the modules. Considerable overshoot and ringing.
• The sensitivity of all 850nm PINs was found to about 3dB worse than the sensitivity of 1310nm PINs.
• The only modules that were able to meet all 13 points of our spec. (Tx, Rx and power) were 850 and 1310nn VCSEL-based SFP+ modules.
PASS PASSFAILFAIL FAIL
Summary• The future Versatile Transceiver will be
– built from radiation-qualified optoelectronic components;– customized from a commercial transceiver.
• Using commercial devices we have developed test methods for transceiver testing to – select a transceiver family for VTRx customization;– test the performance of the prototype VTRx modules.
• The results from our evaluation of several commercial transceiver modules show that– the SFP+ is the most suitable candidate for VTRx customization;– to achieve low power dissipation we need to target VCSEL-based lasers;– there are 1310nm VCSEL diodes capable of being operated at 5Gbps
with sufficient performance.TWEPP 2008
250
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50
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# H
its
-25 -20 -15 -10 -5 0 5 10 15 20 25
ps
LoopbackUsing Optical
Reference TxUsing a
-21.0
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dB
m
54321
TRx Device #
Using Optical Loopback
Using a Reference Tx
Rx Performance Evaluation – Alternative
Receiver
Transmitter
SDA Scope
PRBS Source
Clock Generator PC
Automation
2m Optical Fiber
Optical Attenuator and Power
Meter
Receiver
Transmitter
FPGA-Based BER Tester
Clock Generator
PC Automation
2m Optical FiberTestboard and DUT
Optical Attenuator and Power
Meter
Setup B’(TRx) Electrical Evaluation
in Optical Loopback
Setup C’(Rx) Sensitivity Evaluation
in Optical Loopback
2m Optical Fiber
2m Optical Fiber
Rx eye, jitter components and bathtub,
mask test
Rx sensitivity
20GHz Electrical Sampling Module
Testboard and DUT
Jitter Histogram - Loopback vs. Reference TxExample Using of the Same Module
Sensitivity - Loopback vs. Reference TxExample Using 5 Units of the Same TRx
• The Rx performance is not decoupled from the Tx.
• The Jitter is from the entire TRx.
• The sensitivity may be different and less consistent.TWEPP 2008
Results – Tx and Power
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1 21 11 0987654321D e v ic e #
# TRx TypePass/FailTx Power
1 SFP 4G 850VCSEL Fail Pass2 SFP 4G 1310VCSEL Fail Pass3 SFP+ 10G 850VCSEL #1 Pass Pass4 SFP+ 10G 850VCSEL #2 Pass Pass5 SFP+ 10G 1310DFB #1 Pass Fail6 SFP+ 10G 1310DFB #2 Pass Fail7 XFP 10G 1310DFB Pass Fail8 SFP+ 10G 1310VCSEL #1 Fail Pass9 SFP+ 10G 1310VCSEL #2 Fail Pass10 SFP+ 10G 1310VCSEL #3 Pass Pass11 SFP+ 10G 1310VCSEL #4 Pass Pass12 SFP+ 10G 1310VCSEL #5 Pass Pass
SFP VCSEL modules: Problems with rise/fall times and jitter. The mask fails.
XFP 1310nm DFB module: Great jitter performance but high power dissipation.
SFP+ 1310mn VCSEL modules: Great power dissipation and good 5Gbps Tx performance in most of the modules. Considerable overshoot and ringing.
SFP+ 850mn VCSEL modules: Good power dissipation and very good 5Gbps Tx performance.
SFP+ 1310mn DFB modules: Good 5Gbps Tx performance but high power dissipation.
850nm VCSEL
1310nm DFB
1310nm VCSEL
1310nm VCSEL
850nm VCSEL
PWR_
FoM
Tx_F
oM
TWEPP 2008
Results – Rx and Overall Performance
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1 21 11 0987654321D e v ic e #Fo
M (a
vera
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3)Rx
_FoM # TRx Type
Pass/FailRx All
1 SFP 4G 850VCSEL Fail Fail2 SFP 4G 1310VCSEL Fail Fail3 SFP+ 10G 850VCSEL #1 Pass Pass4 SFP+ 10G 850VCSEL #2 Pass Pass5 SFP+ 10G 1310DFB #1 Pass Fail6 SFP+ 10G 1310DFB #2 Pass Fail7 XFP 10G 1310DFB Pass Fail8 SFP+ 10G 1310VCSEL #1 Pass Fail9 SFP+ 10G 1310VCSEL #2 Pass Fail10 SFP+ 10G 1310VCSEL #3 Pass Pass11 SFP+ 10G 1310VCSEL #4 Pass Pass12 SFP+ 10G 1310VCSEL #5 Pass Pass
SFP modules: Our jitter spec. is too harsh for 4G SFP receivers. Also their electrical swing can be much higher than is allowed by our mask.
Modules with 1310nm PINs: The sensitivity at 1E-12 was found to be around -19dBm (about 3dB better than with 850nm PINs).
SFP+ with 850nm PINs: Using an input with an OMA of 90uW (spec.), the jitter seems not to be made worse by the lower sensitivity of 850nm PINs. Using this OMA the jitter seems to depend mostly on the electronics, i.e. TIA, LA and PCB design.
The only modules that were able to meet all 13 points of our spec. (Tx, Rx and power) were 850 and 1310nn VCSEL-based SFP+ modules.
Fall, Rx Jitt
er, Tx
and Rx Mask
Tx and Rx Jitter
and Mask Power
dissipationOMA and Tx
maskTx mask
TWEPP 2008