K.K. Gan B Layer Workshop 1

Rad-Hard Opto-Link Upgrade

September 30, 2007

K.K. GanThe Ohio State University

K.K. Gan B Layer Workshop 2

Outline

● Upgrade plan/requirements● Bandwidth of micro twisted-pair cables● Bandwidth of fusion spliced SIMM-GRIN fibers● Radiation hardness/speed of PIN/VCSEL arrays

K.K. Gan B Layer Workshop 3

Current Opto-Link Architecture

● Plan: upgrade based on current pixel link architectureto take advantage of R&D effort and production experience

micro twisted pairs decouple pixel and opto module simplify both design/production

8 m of rad-hard/low-bandwidthSIMM fiber fusion spliced to 70 m rad-tolerant/medium-bandwidthGRIN fiber

K.K. Gan B Layer Workshop 4

Proposed Opto-Link Architecture

DORIC

VDC VCSEL

PIN

PIN

VCSEL BPM

DRX 80 Mb/sROD

40 MHzCLK

Commands

Data

1 m wires 80 m fibers

FE/MCC

Opto-board

TTC

DORIC

VCSEL

PIN

PIN

VCSEL BPM

DRX 640 Mb/sROD

160 MHz

FE

TTC

160 Mb/s

Serializer/VDC

Current:

Proposed:

K.K. Gan B Layer Workshop 5

Possible GBT-Lite ArchitectureXCK (160 MHz)

DTO 1800 Mb/s8b/10b

SEU TolerantSerializerModule 1

(160 Mb/s)

SEU TolerantSerializer

8b/10bEncoder

8b/10bEncoder

CLK 4X CLK 5X

Module n(160 Mb/s)

DTO n800 Mb/s8b/10b

K.K. Gan B Layer Workshop 6

Case for DC Balancing in Opto-Link

● some VCSELs require µs to produce full optical power● Pixel TTC opto-link has been quite easy to operate● commercial high speed opto links are mostly DC balanced DC balancing will likely make a more robust uplink!

K.K. Gan B Layer Workshop 7

Increasing Functionality in VDC?

● lost of VCSEL:■ add capability to reroute data in VDC to spare VCSEL?

● difficult to operate present data links due to optical power spread in VCSEL arrays:■ add current adjustment for each VCSEL channel?

K.K. Gan B Layer Workshop 8

VDC with Rerouting Capability?

DTO(800Mb/s)

DTO(800 Mb/s)

LVDS“like”

Receiver

ControlInterpreter

Control Lines From DORIC

1.5 to 2.5 VLogic

Translator

VDD = 1.5 V VDD = 2.5 V

VCSELDriver

SEUTolerant

DACs

ISET &IBIAS

1.5 to 2.5 VLogic

Translator

VCSELDriver

SEUTolerant

DACs

ISET &IBIAS

K.K. Gan B Layer Workshop 9

VDC Status

● thick oxide (2.5 V) transistors are enclosed devices● extracted simulations indicate bandwidth > 1 Gb/s

K.K. Gan B Layer Workshop 10

DORIC Status

● simulations of transimpedance amplifier + limiting amplifier yield 50% duty cycle for input current of 20-1000 µA

● preliminary simulations of LVDS “like” driver promising

160 Mb/sBPM

EncodedTTC

XCK (160 MHz)

DCI (160 Mb/s)

TIA

LimitingAmp

ClockRecovery

Circuit

DataRecovery

Circuit

LVDS“like”Driver

LVDS“like”Driver

CommandDecoder

VDC Control Lines

K.K. Gan B Layer Workshop 11

Upgrade Feasibility with Present Infrastructure

● can micro twisted pair transmit at 160 MHz?● can PIN operate at 160 MHz?● can PIN array survive B-layer radiation dosage?● can high-speed VCSEL array survive B-layer radiation dosage?● can fusion spliced SIMM/GRIN fiber transmit at 640 Mb/s?● we already know some of the answers from SLHC R&D

K.K. Gan B Layer Workshop 12

Bandwidth of Micro Twisted Pairs

(current pixel cable)

● current pixel cable with thick insulation is quite optimum!

K.K. Gan B Layer Workshop 13

Eye Diagrams100 µm current pixel cable

60 cm

● transmission at 640 Mb/s is adequate● transmission at 1280 Mb/s may be acceptable● 127 µm cable is slightly better

640 Mb/s

1280 Mb/s

140 cm127 µm cable

140 cm

K.K. Gan B Layer Workshop 14

Bandwidth of Fusion Spliced Fiber8 + 80 m spliced SIMM/GRIN fiber1 m GRIN fiber

● transmission up to 2 Gb/s looks adequate current fibers can be reused● current system uses 6-7 channels in 8-channel array/ribbon ● some spare ribbons were installed can have modest increase in # pixel modules

2 Gb/s

K.K. Gan B Layer Workshop 15

PIN Responsivity

● Si PIN responsivity decreases by 65% after SLHC dosage● operation at 160 MHz is OK● completed irradiation of GaAs PIN from 3 vendors:

■ Optowell, AOC, ULM ■ responsivities will be measured soon

0

2

4

6

8

10

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7

Pre-irradPost-irrad

Co

un

t

Responsivity (A/W)

K.K. Gan B Layer Workshop 16

VCSEL Power vs Dosage

2007 preliminaryTwo arrays each(2 x 7 channels)

1st irradiationperiod

2nd irradiationperiod

● irradiated VCSELs from 3 vendors to SLHC dosage● all are acceptable for B layer replacement

LHC

K.K. Gan B Layer Workshop 17

Opto-Pack Development● current pixel detector uses Taiwan optical packages

VCSEL mounted on PCB with poor heat conduction micro soldering of 250 µm leads is difficult

● Ohio State develops new opto-pack for SLHC■ uses BeO base with 3D traces for efficient heat removal■ wire bond to driver/receiver chip

OSU

Taiwan

K.K. Gan B Layer Workshop 18

Results on Opto-Packs● 35 VCSEL & 6 PIN opto-packs have been fabricated

◆ all VCSEL opto-packs except one have good coupled power principle of new opto-pack has been demonstrated

MT ferrule

Ceramic guide pin

VCSEL array

1 cm

K.K. Gan B Layer Workshop 19

Summary● Simple VDC design completed

❏ VDC with more functionality proposed● DORIC design in progress✔ micro twisted-pair cable of current ATLAS pixel detector

can be used for transmission up to 1 Gb/s✔ fusion spliced SIMM/GRIN fiber can transmit up to 2 Gb/s✔ Si PIN can be operated up to 160 MHz

❏ GaAs PIN evaluation in progress✔ good high speed VCSELs from 3 vendors✔ compact MT-style opto-pack based on BeO has been developed current opto-link architecture satisfies B-layer requirements