[e-mail] www.hep.ph.ic.ac.uk/~hallg/

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Electronic requirements for detectors

• Use LHC systems to illustrate

physics technical
Tracking high spatial precision large channel count limited energy precision limited dynamic range low power mW/channel high radiation levels 10Mrad
Calorimetry high energy resolution large energy range excellent linearity very stable over time intermediate radiation levels 0.5Mrad power constraints
Muons very large area moderate spatial resolution accurate alignment stability low radiation levels
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Generic LHC readout system

• functions required by all systems
• amplification and filtering
• analogue to digital conversion
• association to beam crossing
• storage prior to trigger
• deadtime free readout _at_ 100kHz
• storage pre-DAQ
• calibration
• control
• monitoring
• CAL Muons special functions
• first level trigger primitive generation
• optional
• location of digitisation memory

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Deadtime free operation

• Pipeline memory
• buffer depth and trigger rate
• determine deadtime
• data often buffered in pipeline
• queueing problem

APV25 NB 10, NP 192 _at_100kHz
compare with deadtime from maximum trigger
sequence 1001 50ns/10µs 0.5
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Basic radiation effects on electronics

• Bipolar
• atomic displacement
• carrier recombination in base
• gain degradation, transistor matching,
• dose rate dependence
• CMOS
• oxide charge trap build-up
• threshold (gate) voltage shift,
• increased noise,
• change of logic state SEU
• All technologies
• parasitic devices created gt Latch-up
• can be destructive

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Why 0.25µm CMOS?

• by 1997 some (confusing) evidence of radiation
  tolerance
• extra thin gate oxide beneficial
• tunnelling of electrons neutralises oxide charge

• negative effects attributed to leakage paths
  around NMOS transistors
• cure with enclosed gate geometry

1Mrad VT vs toxide
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First results from 0.25µm CMOS (1997)

• technology thought to be viable for intermediate
  radiation levels (300krad)
• but results much better than expected

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Tracking systems

• ATLAS
• Innermost Pixels
• Inner Silicon microstrips 6M channels
• Occupancy 1-2
• Outer Transition Radiation tracker
• gas filled 4mm diameter straw tubes 420k
  channels
• x-ray signals from e- above TR threshold
• occupancy 40
• CMS
• Innermost Pixels
• Remainder Silicon microstrips 10M channels
• Occupancy 1-2
• Radiation hardness is a crucial point for trackers

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ATLAS TRT readout

• ASDBLR amplifier/shaper/discriminator
• key points
• speed and stability, since high occupancy
• peaking time 7-8ns gt reduce pileup
• baseline restorer gt maintain threshold levels
• two level discriminator gt electron
  identification

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ATLAS TRT ASDBLR front end

• Amplifier gttail cancellation and baseline
  restoration
• selectable for CF4 and Xe gas mixtures

4mm straw Xenon based gas
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ATLAS SCT front end

• Amplifier/discriminator pipeline/sparse readout
  ABCD (BiCMOS)
• Binary readout
• simple
• small data volume
• but
• maintain 6M thresholds
• vulnerable to common mode noise
• Specifications
• ENC lt 1500e
• Efficiency 99
• Bunch crossing tag 1 bunch crossing
• Noise occupancy 5x10-4
• Double pulse resolution 50ns after 3.5fC signal
• Derandomising buffer 8 deep
• Power lt3.8mW/channel

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CMS microstrip tracker readout

• 10 million detector channels
• Analogue readout
• synchronous system
• no zero suppression
• maximal information
• improved operation, performance and monitoring
• 0.25µm CMOS technology
• intrinsic radiation hardness
• Off-detector digitisation
• analogue optical data transmission
• reduce custom radiation-hard electronics

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Impulse deconvolution at LHC

• High speed signal processing is required to match
  the 40MHz beam crossings
• Low power consumption is essential -
  2-3mW/channel
• Performance must be maintained after irradiation
• Start from CR-RC filter waveform
• form weighted sum of pulse samples
• zero response outside narrow time window
• small number of weights (gt3)
• implementable in CMOS switched capacitor filter

Ideal CR-RC
Sampled CR-RC waveform
Deconvoluted waveform
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Pulse shapes noise APV25

1 MIP signal
t ns
ENC electrons

• System specification
• Noise lt2000 electrons for CMS lifetime

Input capacitance pF
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Calorimeter systems

• ATLAS ECAL/Endcap HCAL
• Liquid Argon 190k channels
• signal triangular current 500ns fall (drift
  time)
• CD 200-2000pF
• ATLAS Barrel HCAL
• Scintillating tiles 10k channels
• CMS ECAL
• PbWO4 crystals APDs (forward VPT)
• 80k channels
• fast signal t 10ns CD 35-100pF
• CMS Barrel/Endcap HCAL
• Cu /scintillating tiles with WLS
• 11k channels HPD readout

Requirements large dynamic range 50MeV-2TeV
92dB 15-16bits precision 12bits and high
stability precise calibration 0.25
Radiation environment few 100krad - Mrad
high neutron fluxes (forward)
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CMS crystal ECAL

• Amplifier close to photo-detector
• (APD or VPT)
• 4 gain amplifier FPU gain selection
• 12bit 40MHz digitisation
• commercial bipolar ADC - rad hard
• 1Gb/s optical transmission
• 12bit (data) 2bit (range)
• custom development using VCSELs
• 80,000 low power links
• Recent substantial changes in philosophy

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Optical links in LHC experiments

• Advantages c.f. copper
• low mass, no electrical interference, low power,
  high bandwidth
• LHC requirements
• digital control 40Ms/s
• digital data transmission 1Gb/s
• analogue 40Ms/s CMS Tracker
• Fast moving technological area
• driven by applications
• digital telecomms, computer links
• analogue cable TV
• requirements c.f. commercial systems
• bulk, power, cost, radiation tolerance ??
• possible for some applications?

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Semiconductor lasers

• Now dominate market, over LEDs
• narrow beam, high optical power, low electrical
  power,
• better matched to fibres
• Direct band gap material
• GaAs 850nm
• GaAlAs 600-900nm
• In, Ga, As, P 0.55-4µm
• Forward biased p-n diode -gt population inversion
• optical cavity gt laser at I gt Ithreshold
• often very linear response
• Fibres and connectors
• sufficient rad hardness
• trackers require miniature connectors
• care with handling compared to electrical

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CMS Tracker analogue optical links

• Edge emitting 1.3µm InGaAsP MQW laser diodes
• miniature devices required
• single mode fibre 50mW/256 detector channels

Tx
Rx
same components for digital control BER ltlt 10-12
easily achievable