The Optical Transmitters The Optical Transmitters for the LHCb L0 Calorimeter Triggerfor the LHCb L0 Calorimeter Trigger

G.Avoni, G. Balbi, A. Carbone, I. D’Antone, D. Galli, I. Lax, U. Marconi and V. Vagnoni,

INFN, Bologna

Introduction Multi-channel Optical TransmitterPart 1

Single-channel Optical Transmitter BER measurements Selection Board

The multi-channel optical transmitter board can host up to 12 optical GOL serializers.

The optical transducer used is a HFBR772BH. 850 nm VCSEL array source 12 independent channels per module. Standard MTP® (MPO) ribbon fiber connector interface. 50/125 µm multimode fiber.

The clock distributor is a NB100LVEP221FA. The jitter introduced is guaranteed to be less than 2ps RMS.

The optical transmitter board receives the control signals and the power from the carrier board through the SAMTEC 0.635 mm Hi-Speed Connectors.

Optical Transducer HFBR772BH

Pluggable packageMPO connector

SAMTEC 0.635 mm Hi-Speed HeaderQTS-125-03-L-D-A 250 pin

connectors

Jumper to setthe I2C address

Clock distributor

NB100LVEP221FA

Using the CRT4T as a power supply switch for the GOLThe L0 trigger system of LHCb is used to reduce the bunch crossing rate of LHC (40.08 MHz) to the 1 MHz rate sustainable for the High Level Trigger.

The calorimeter system of LHCb is used to select the highest energetic clusters in the ECAL (electromagnetic calorimeters) or HCAL (hadronic calorimeters) for the L0 calorimeter trigger.

The cluster energy is measured on 2x2 cells at the front-end board, from 8x8 cm2 (inner ECAL) to 52x52 cm2 (outer HCAL).

ECAL is segmented in 5952 cells (each cell is a possible cluster). Validation (determine the cluster type) is done by the PS/SPD (some geometry) to get the electron and photon candidates. Combination of the detector signal to select π0 candidates are also foreseen.

HCAL is segmented in 1484 cells (each cell is a possible cluster). Addition of the energy possibly lost in ECAL if available.

The 32 channels front end board selects a cluster as a local maximum energy deposit.

Signal from the auxiliary detectors SPD and Pre-Showerare used in the Validation phase to assess the cluster type.

Attenuation (dB)

Eye Top (μW) Time (hours) Errors (C.L.95%)

0 293.6 24 <10-13

3 143.3 24 <10-13

6 72.34 120 <10-14

9 36.12 24 <10-13

12 18.39 24 <10-13

13.9 11.92 ½ Errors observed

Eye top 293.6 μW Eye top 143.3 μW

Attenuation 0 dB Attenuation 3 dB Attenuation 14 dB

Eye top 11.92 μW

Attenuation of the light pulses has been varied to establish the range within the transmission is errors free. Data shall go through 100m long cables and two optical patch panels

VCSEL with SMA threaded connector

GOL

Control Status LED 40 mm

SAMTEC High Speed Connectors 0.635mm Hi-Speed Header QTS and QSS series

Dip switch to set the GOL I2C address

Solder switch to control the VCSEL bias current, set at the production to grant optimal

performance

TOP SIDE VIEW BOTTOM SIDE VIEW

• VCSEL Laser ULM850-05-TN USMB0P by ULM Photonics.

• High speed, up to 2.5 Gbps.

• SMA fibre connector.

• Operate on multimode fibre at wavelength of 850nm.

• The VCSEL option considered is that of 1mW @ 6mA.

Clock 40MHz

Controls

32 data bits

ConnectorsGOL

Power

To fiber

Attenuation of the light pulses has been varied to establish the range within the transmission is errors

free. Data shall go through 100m long cables and two

optical patch panels

Eye top 462.8 μW Eye top 57.6 μW Eye top 18.29 μW

Attenuation 9 dB Attenuation 0 dB Attenuation 14 dB

L0 Calorimeter Trigger

Logical Scheme

L1 Buffer

FE boards 8x4 input channels

Validation Cards

10m cables

LVDS connections

Optical links100m fibers

Selection Boards

Optical links5m fibers

BER n(bits) t

10-12 2.3·1012 30 min

10-13 2.3·1013 5 h

10-14 2.3·1014 50 h

The Selection Boards receives data from the Validation Cards through the optical links. Each board is equipped with 30 optical receivers (28+2 spares).

For the ECS (Experimental Control System) an on-board Credit Card PC has been adopted for local configuration and monitoring by interfacing with i2c buses, jtag chains and a 32-bit parallel local bus.

The quality of the clock used to drive the GOL serializer is a critical parameter.The GOL maximum tolerable jitter value is 100 ps (peak-to-peak).The clock signal from the LHC TTC (Timing Trigger and Control) system to the GOL is distributed to the Optical Transmitter board from the Carrier Board through the connector clock pin and then distributed by the NB100LVEP221FA.The quality of the clock measured at the GOL clock pin after having passed through the entire distribution chain shows rather a good σ value of about 7 ps.

The clock signal used to drive the optical mezzanine presents a jitter of σ = 14.34 ps (picture on the left). The quality of the jitter at the pin clock of the GOL

improves σ = 6.95 ps due a QPLL filter used in the carrier boards.

40.08MHz

Control

12x32 bits data

Connectors

GOL

x12

GOL

x12

Parallel FiberAGILENT

12 Ch

clock Distributor

Power

12x1.6 Gbps

CRT4T

80 mt. fiber 1.6 Gb/s

Transmitterboard

TTCrq

Receiverboard

TektronixCSA 7404

Scope

BERT

XilinixFPGA

TektronixTLA 720

Logic Analyzer

nx32bit

nx32bit

40.08MHz

80.160MHz

RxBoard

TxBoard

First method: direct comparison of the transmitted and received patterns.

The optical attenuator used in our test is the Amphenol AFO 46946. it is an adjustable attenuator without pre-definite steps. The attenuation level can be varied by rotating a milled ring.

Attenuator:Amphenol AFO

46946

To reach a sensitivity of 10-12 in measuring the transmission error probability with this technique, when no error is detected during the entire data transmission, aiming a confidence level of 90%, lasts about 30 minutes.

receivedbitstotal

errorinreceivedbitsBER

__

___

To implement the GOL power switch, two PMOS devices are used in parallel in order to reduce the “on” resistance of the switch (this reduces the voltage drop across the switch). An NMOS device is additionally used to short the GOL power to ground when the power switch is open. This device guarantees that the GOL power supply rail is pulled to ground even in the presence of active inputs.

QeSNR

erfcBER

Q

222

1 2

2

Second method: eye diagram analysis

12th Workshop on Electronics for LHC and Future Experiments – Valencia, Spain – 25-29 September 2006

Top view

Bottom view

VCSEL

The GOL ASIC is packaged in a 144-pin

fpBGA 13 mm side package with 1mm solder-ball pitch.

1mm

Vcc

OFF/ ON

GOL

CRT4T

Meg-Array ® 100 Position Plug, 0.00 mm Stack Height, 1.27 mm x 1.27 mm ( 0.050 in. x 0.050 in.) Centerline --

FCI84512-102

01

01

Q

Inter-board communication goes through a dedicated interface and a point-to-point connector. It is used to transmit partial results from one board to another.

Power from the TELL1 custom backplane

ECSinterface

Attenuation (dB)

Eye Top (μW) Time (hours) Errors (C.L.95%)

0 462,8 24 <10-13

3 232 24 <10-13

6 114,5 120 <10-14

9 57,6 24 <10-13

12 27,34 24 <10-13

14 18,29 24 Errors Observed

BER vs. Optical Attenuation

BER vs. Optical Attenuation Bottomview

Multi-channel Optical TransmitterPart 2

Pseudo Random Pattern

SequenceGenerator

The TTCrq contains a TTCrx, a QPLL with its

associated crystal and a TrueLight pin-preamplifier

The “Q” value has been measured with the digital scope embedded software, specifically developed by Tektronix for eye-diagram analysis.This formula returns estimated values better than 10-13.

TTCrq

30 channels Optical Receivers and deserializers

3 channels Optical

Transmitters

ProcessFPGA

LAN

The board (VME 9U standard, 2.4mm total thickness) consists in 16 layers.

Temperature sensors allow monitoring of several areas of the board.

Critical signals are routed differentially.

Special care has been taken to improve several points:- controlled line impedance of for the clock and serial data lines;- similar length of the traces between different deserializers;- signal integrity, by minimizing crosstalk and reflections.

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