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Production of the LHCb Silicon Tracker Readout Electronics. Outline. Overview of the Readout Electronics 1st preproduction of Digitizer Board Evaluation of performance Integration with LHCb hardware 2nd preproduction Conclusion. LHCb Silicon Tracker principle.

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Production of the lhcb silicon tracker readout electronics l.jpg
Production of the LHCb Silicon Tracker Readout Electronics

A. Vollhardt, EPF Lausanne/Switzerland

Outline l.jpg

  • Overview of the Readout Electronics

  • 1st preproduction of Digitizer Board

  • Evaluation of performance

  • Integration with LHCb hardware

  • 2nd preproduction

  • Conclusion

A. Vollhardt, EPF Lausanne/Switzerland

Lhcb silicon tracker principle l.jpg
LHCb Silicon Tracker principle

  • Two distinct tracking systems based on silicon strip detectors, read out via the BEETLE chip

  • TT: full acceptance angle covered upstream of magnet

  • IT: only area of highest track densities around beampipe

A. Vollhardt, EPF Lausanne/Switzerland

Beetle readout chip l.jpg
Beetle readout chip

  • 128 channel charge integrator

  • polyimide readout hybrid carries 3 (IT) or 4 (TT) Beetle chips for sensors of 384 (IT) or 512 (TT) strips

    See also:

  • Talk of F. Lehner: Hybrid Design, Procurement and Testing for the LHCb Silicon Tracker

A. Vollhardt, EPF Lausanne/Switzerland

St readout electronics l.jpg
ST Readout electronics

A. Vollhardt, EPF Lausanne/Switzerland

Service box overview l.jpg

low-voltage power

Service Box Overview

sensor + readouthybrids

5m copper cable

Optical fibres for physics data

Digitizer Board

up to 16 hybrids/boards

Digitizer Board

Control Card




A. Vollhardt, EPF Lausanne/Switzerland

Digitizer board characteristics l.jpg
Digitizer Board characteristics

  • 6 layer PCB, halogen-free, 1.6 mm thickness, symmetric stack

  • single side mounting, no buried/blind vias

  • smallest feature size 6 mil, smallest package 0603

  • 5 BGA devices: 1x CS49 (0.8 mm pitch), 3-4x BGA144(1.0 mm pitch)

  • no JTAG chain , no boundary scan

  • differential traces have controlled impedance/length

  • standard commercial connectors

  • NO tuning points

  • layout optimized for low-cost, high-yield, easy testing

    2 versions: Trigger Tracker (4-chip readout), Inner Tracker (3-chip readout)

A. Vollhardt, EPF Lausanne/Switzerland

1 preproduction run l.jpg
1. Preproduction run

  • 17 boards produced and electrically tested in late 2004(TT version)

  • after assembly, all BGAs X-rayed: all solder joints ok!

  • 2 bugfixes:wrong reference voltage for line receiverAuto-Sync FPGA: shift register one cycle (25ns) too short

  • all boards except one immediately working:board #10 had ripped via under BGA (fixed)

    changes for IT version preproduction (and final production):

  • changed VCSEL biasing

  • added QPLL RC-network for improved jitter stability

A. Vollhardt, EPF Lausanne/Switzerland

Digitizer board l.jpg
Digitizer Board

  • Power <5 W

  • Only positive voltages: 2.5 V, 5.0 V

A. Vollhardt, EPF Lausanne/Switzerland

Beetle signal at adc l.jpg
Beetle signal at ADC

  • Flat top 15 nsec wide (of 25 nsec max.)

  • measured with 5m twisted pair cable

  • plenty of ‘space’ to set ADC sampling point

A. Vollhardt, EPF Lausanne/Switzerland

Linearity l.jpg

A. Vollhardt, EPF Lausanne/Switzerland

Sampling synchronicity i l.jpg
Sampling synchronicity I

  • supply all 16 inputs with ‘synchronous’ testpulse:testpulse generator sourcing 16 LVDS drivers

  • move sampling time by using TTCrx clock phase shifters (just like in experiment..)

  • transmit data via GOL+ optical fibres to DACs and scope

  • record pulseheight of sampled edge vs. programmed delay

A. Vollhardt, EPF Lausanne/Switzerland

Sampling synchronicity ii l.jpg
Sampling synchronicity II

A. Vollhardt, EPF Lausanne/Switzerland

Gol vcsel connection l.jpg
GOL VCSEL connection

  • VCSEL forward voltage with 2.5V anode voltage results in too low GOL current driver voltage level

  • only 2.5V and 5V available

  • reduced to 3.3V by low-impedance divider

  • blocked at VCSEL with 100nF||100pF

A. Vollhardt, EPF Lausanne/Switzerland

Eye diagram after 100m l.jpg
Eye diagram after 100m

  • Thanks to Paolo Ciambrone/LHCb Muon

A. Vollhardt, EPF Lausanne/Switzerland

Auto sync l.jpg

Beetle analogue output

  • Beetle DataValid signal (almost) in parallel to analogue data to frame a triggered event

  • done via shift register in Actel antifuse FPGA (small version of rad-hard AX54SX32) incl. TMR+ majority voting

  • Results in at least one IDLE frame per event

Beetle DataValid

Beetle data after digitization

DataValid after 200 ns delay

A. Vollhardt, EPF Lausanne/Switzerland

Radiation qualification l.jpg
Radiation qualification

  • Expected radiation levels for Service Box location for 10 years:TID 15 krad, NIEL 2E12 n/cm2

  • all commercial devices individually radiation qualified (TID, NIEL and SEE) with proton and neutron irradiation according to LHCb radiation policy

  • System test: TT Digitizer Board + backplane re-tested in June 2005 with 60 MeV protons to 60 krad (PSI, Switzerland):

    • analogue test pattern injected

    • verification of function and performance

    • no variations in module operation observed

A. Vollhardt, EPF Lausanne/Switzerland

Full readout test l.jpg
Full Readout test

A. Vollhardt, EPF Lausanne/Switzerland

Full readout test19 l.jpg
Full Readout test

  • LHCb-style readout (except LHCb Readout Supervisor + CPU farm)

A. Vollhardt, EPF Lausanne/Switzerland

Control card l.jpg
Control Card

  • Under development by Universidade de Santiago de Compostela

  • Provides TTC signals and slow control interface to each Service Box and its associated frontend electronics

  • First prototype functional (still being tested)

A. Vollhardt, EPF Lausanne/Switzerland

Breaking news it version l.jpg
Breaking News: IT version

  • 10 Digitizer Boards (IT version preproduction) were delivered last Wednesday

  • initial testing confirm out-of-the-box functionality

  • important step: re-validate eye diagram with new VCSEL bias!

A. Vollhardt, EPF Lausanne/Switzerland

Next steps l.jpg
Next steps

  • detailed testing of IT prototypes: last design verification

  • launch production order after:

    • production+assembly time for all boards: ca. 8-10 weeks

    • all parts available except for VCSELs (LHCb common order placed, expected in November)

    • ‘bird-food’ supplied by company, special components by us

  • start setting up test bench during production:basic functionality test (go-nogo)burn-in test (catch infant mortality)

A. Vollhardt, EPF Lausanne/Switzerland

Conclusion outlook l.jpg
Conclusion + Outlook

  • The preseries production for both versions of the ST Digitizer Board has been completed.

  • Bugfixes and lessons learned in the TT version were successfully included in the IT version.

  • Required functionality was verified and system compatibility with common LHCb hardware has been shown.

  • Preseries hardware is used to form teststands for the TT sensor module production (Zuerich) and the IT sensor production (CERN)

  • Final qualification pending, design will be released for full production in Q4/05.

A. Vollhardt, EPF Lausanne/Switzerland

Spare slides l.jpg

A. Vollhardt, EPF Lausanne/Switzerland

Digitizer board input stage l.jpg

2.5 V

3x 1 kW

differential signal from Beetle

Vref (ca. 1 V)

Output to GOL serializer

10 kW

39 W




22 W


2x 100 nF


8 bits



100 nF

39 W

gain: 11

gain: 0.22impedance: 100 Ohm

Digitizer Board input stage

  • Bandwidth: 1.6 kHz (AC-Coupling) to 170 MHz (AD8129)

  • Amplifier output range matches ADC input range

A. Vollhardt, EPF Lausanne/Switzerland

Clock tree l.jpg
Clock tree

A. Vollhardt, EPF Lausanne/Switzerland

Tfc distribution l.jpg
TFC distribution

  • Impedance controlled traces for LVDS signals

  • TTL traces only used for short (~ 2 cm) for fanning out

  • equal trace lengths to minimize ch-ch skew

A. Vollhardt, EPF Lausanne/Switzerland

Service box frame l.jpg
Service Box: frame

  • Fully loaded weight: ca. 10 kg

  • Power disipation: ca. 150 W (70 W into mixed water cooled heatsink)

A. Vollhardt, EPF Lausanne/Switzerland

Service box cooling l.jpg
Service Box cooling

  • all linear regulators located close to each other

  • use common copper heatsink (mixed water) to cool all at once

  • isolate ground slug of regulator package (local ground!)

  • used for testing: CPU water cooling system: no active cooler, but fan-blown heat-exchanger

  • Test at full load results in 35 degC case temperature for 25 degC water (=ambient temperature)

A. Vollhardt, EPF Lausanne/Switzerland

It mounting l.jpg
IT mounting

  • Service Boxes outside acceptance

  • Mounted on common IT station frame

  • ‘5m copper cables’ no not move

  • cables from Service Box away from detector move (cable chains)

A. Vollhardt, EPF Lausanne/Switzerland

Tt mounting l.jpg
TT mounting

  • Service Boxes mounted outside acceptance to magnet

  • ‘5m copper cable’ guided in cable chains to station halves

  • cables away from Service Box fixed in cable trays

A. Vollhardt, EPF Lausanne/Switzerland