© intec 2000 reasons for parallel optical interconnects roel baets ghent university - imec...
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![Page 1: © intec 2000 Reasons for parallel optical interconnects Roel Baets Ghent University - IMEC Department of Information Technology (INTEC)](https://reader030.vdocuments.us/reader030/viewer/2022032704/56649d4b5503460f94a2950d/html5/thumbnails/1.jpg)
© intec 2000
Reasons for parallel optical interconnects
Roel Baets
Ghent University - IMEC
Department of Information Technology (INTEC)
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http://www.intec.ugent.be/IODate workshop, February 2004
Overview
• Introduction
• Electrical interconnects: the limitations
• Optical interconnects: the merits
• Optical interconnects: the challenges
• Conclusion
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http://www.intec.ugent.be/IODate workshop, February 2004
Interconnect: what ?
Interconnects = transmission of information
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http://www.intec.ugent.be/IODate workshop, February 2004
Optical interconnects
Optical interconnects is a success for telecommunication
long-distance (several km)
shorter distance (tens to hundreds meters): data-communications (LAN) system-level interconnects
(parallel optical datalinks)
And shorter distance is electrical ?
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http://www.intec.ugent.be/IODate workshop, February 2004
Electrical connections (1)
Electrical tracks on PCB exhibit high loss
Solution pre-emphasis driver = higher-power dissipation
repeaters = higher power dissipation + more real estate
1m 8mil 50 stripguide with GETEK dielectric
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http://www.intec.ugent.be/IODate workshop, February 2004
Electrical interconnects (2)
Electrical connectors are large
= a density problem
Electrical connector at best 2 Gbps/mm2
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http://www.intec.ugent.be/IODate workshop, February 2004
Progress electrical interconnects
ITRS Roadmap 2003:
chip-to board for peripheral busses is 5 to 6 Gbps for differential pairs in 2008-2009
but limited to a small number of pins
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http://www.intec.ugent.be/IODate workshop, February 2004
Optical interconnects !
Shorter-distance interconnects benefit from optical technologies !
A good reason for optical interconnects:
optics is better than electrical interconnects
in terms of
power dissipation is distance independent
data density: Gbps per mm2 is larger
transmission distance: loss in fibre is negligible and data rate independent
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http://www.intec.ugent.be/IODate workshop, February 2004
Parallel optics: merits
Reduced power dissipation, especially for long-distance Typical power dissipation per link, for 2.5 Gbps, is 20-30mW
Larger data density due to 2-D parallelism ! Electrical backplane connector is limited to 50 Gbps/cm
Optical backplane connector allows >50 Gbps/mm2 , thus few Tbps/cm
100
1000
10000
100000
1000000
maximal bandwidth over 60cm backpanel
[Gbps]
optical -upper limit
optical - IOconnectors
electrical -upper limit
electrical -state-of-the-art
ATCA backpanel extrapolated to 12.5Gbps line rate
Assuming 250um pitch(smaller pitch is possible) B=B0A/L2
(D.A.B. Miller)
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http://www.intec.ugent.be/IODate workshop, February 2004
Parallel optics: merits
Longer transmission distances optical loss is <1dB/m, loss electrical track on backplane is
>5dB (1m @ 2.5Gbps)
Smaller chip size opto driver and receiver circuit is comparable to (or even
smaller than) LVDS circuit (for given technology)
Simpler system design !! optical path replaces high-speed electrical tracks, thus simpler
packaging and PCBs
optics is scalable: same transceiver for intra-board, board-to-board AND system-to-system interconnects !
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http://www.intec.ugent.be/IODate workshop, February 2004
Optical interconnects ?
So why is optics not yet inside your computer today ?
Optics is a new technology (30 years younger than electronics), components are available only recently
Optics integration requires different novel technologies, optics seems complex
Performance of electrical interconnects is acceptable for current applications
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http://www.intec.ugent.be/IODate workshop, February 2004
Optics: where and when ?
ElectricalElectrical
According to different roadmaps, optical interconnects will be introduced in system around 2008:
Source: INTEL (2002)
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http://www.intec.ugent.be/IODate workshop, February 2004
Interfacing optics to CMOS
Optical interconnect needs
ED: digital CMOS circuitry
EA: analog driver + receiver circuitry
OE: light sources (or modulators) and detectors
O: passive optical pathway (fiber, waveguides in board, free space)
Options:
EA+OE+interface to O in one package
in some applications: ED+EA+OE+O in one package
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http://www.intec.ugent.be/IODate workshop, February 2004
Building OE on electronic ICs
Key challenges:
• integration of OE components on EA chipsyield
cost
• packaging of this chip to allow for interfacing to optical pathway
alignment issues
hermeticity issues
thermal issues
• integration of optical interconnect into the IC design methodology
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http://www.intec.ugent.be/IODate workshop, February 2004
320Gbps160Gbps
80Gbps
40Gbps
On-chip optical access: roadmap
Degree of parallelism
1.25Gbps
2.5Gbps
3.125Gbps
5Gbps
10Gbps
CMOS technology
0.35um
0.18um
0.13um
90nm
4x8
8x8
2x8
x8
16
x16
12.5Gbps
2x1
6x1
6
65nm
4x4
16 32 64 128 256 512 #channels
Feasible today8
1x8
2x8
4x8
x8
640Gbps
1.2Tbps
2.5Tbps
Feasible with future IC
technologies
Fine-pitch optics
Line-rate(over backpanel !!!)
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http://www.intec.ugent.be/IODate workshop, February 2004
Conclusions
The road ahead
Bridge the 30-years age gap with electrical interconnects
(extra) proof of reliability
Offer an integrated solution
Bring all components vendors together
Optimise performance of components to get an efficient and cost-effective link
Cooperate with the end-user