Transcript LHC front end electronics - HEP Group Research Pages

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
www.hep.ph.ic.ac.uk/~hallg/
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[email protected]
November 2001
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 @ ~100kHz
storage pre-DAQ
calibration
control
monitoring
•CAL & Muons special functions
first level trigger primitive generation
•optional
location of digitisation & memory
[email protected]
www.hep.ph.ic.ac.uk/~hallg/
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November 2001
“Deadtime free” operation
•Pipeline memory
buffer depth and trigger rate
determine deadtime
data often buffered in pipeline
queueing problem
APV25
NB ≈ 10, NP =192 @100kHz
compare with deadtime from maximum
trigger sequence = 1001…
= 50ns/10µs = 0.5%
[email protected]
www.hep.ph.ic.ac.uk/~hallg/
3
November 2001
Basic radiation effects on electronics
• Bipolar
atomic displacement
carrier recombination in base
base
IE
gain degradation, transistor matching,
dose rate dependence
collector
emitter
n++
n
p+
IB
• CMOS
oxide charge & trap build-up
threshold (gate) voltage shift,
increased noise,…
change of logic state = SEU
• All technologies
parasitic devices created => Latch-up
can be destructive
[email protected]
www.hep.ph.ic.ac.uk/~hallg/
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November 2001
IC
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
[email protected]
www.hep.ph.ic.ac.uk/~hallg/
1Mrad VT vs toxide
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November 2001
First results from 0.25µm CMOS (1997)
•technology thought to be viable for intermediate radiation levels (~300krad)
but results much better than expected
[email protected]
www.hep.ph.ic.ac.uk/~hallg/
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November 2001
Tracking systems
•ATLAS
•Innermost: Pixels
•Inner:
Silicon microstrips
Occupancy 1-2%
6M channels
•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
Occupancy 1-2%
10M channels
•Radiation hardness is a crucial point for trackers
[email protected]
www.hep.ph.ic.ac.uk/~hallg/
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November 2001
ATLAS TRT readout
•ASDBLR
amplifier/shaper/discriminator
•key points
speed and stability, since high occupancy
peaking time 7-8ns => reduce pileup
baseline restorer => maintain threshold levels
two level discriminator => electron identification
[email protected]
www.hep.ph.ic.ac.uk/~hallg/
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November 2001
ATLAS TRT ASDBLR front end
•Amplifier =>tail cancellation and baseline restoration
selectable for CF4 and Xe gas mixtures
4mm straw + Xenon
based gas
[email protected]
www.hep.ph.ic.ac.uk/~hallg/
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November 2001
•Amplifier/discriminator + pipeline/sparse readout ABCD (BiCMOS)
•Binary readout
Write
simple
Amplifier
small data volume
but
128 x 128
pipeline
maintain 6M thresholds
vulnerable to common mode noise
•Specifications
ENC
Efficiency
Bunch crossing tag
Noise occupancy
Double pulse resolution
Derandomising buffer
Power
[email protected]
Discriminator
Read
< 1500e
99%
1 bunch crossing
5x10-4
50ns after 3.5fC signal
8 deep
<3.8mW/channel
www.hep.ph.ic.ac.uk/~hallg/
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Compress, Format,
Control
ATLAS SCT front end
R/O buffer
November 2001
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
[email protected]
www.hep.ph.ic.ac.uk/~hallg/
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November 2001
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
Ideal CR-RC
w(t)= aoutside
.h(t)+a2.h(tt)+atime
.h(t-2window
t)
1
3
zero response
narrow
small number of weights (>3)
implementable in CMOS switched capacitor filter
Sampled CR-RC
waveform
[email protected]
www.hep.ph.ic.ac.uk/~hallg/
Deconvoluted
waveform
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November 2001
Pulse shapes & noise
APV25
1 MIP signal
125
•
2pF
4p1
8p1
10p7
14p5
17p5
20p5
100
75
50
25
2000
0
50
200
1600
250
ENC [electrons]
0
100t [ns]
150
closed symbols: peak mode: 270 + 38/pF
open symbols:deconvolution: 430 + 61/pF
1200
•System specification
Noise <2000 electrons
for CMS lifetime
800
400
0
-10
[email protected]
chan 2
chan 43
chan 107
www.hep.ph.ic.ac.uk/~hallg/
-5
0
13
5
10
15
20
25
Input capacitance [pF]
November 2001
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
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)
11k channels HPD readout
[email protected]
www.hep.ph.ic.ac.uk/~hallg/
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November 2001
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
[email protected]
www.hep.ph.ic.ac.uk/~hallg/
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November 2001
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?
[email protected]
www.hep.ph.ic.ac.uk/~hallg/
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November 2001
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 -> population inversion
optical cavity => laser at I > Ithreshold
often very linear response
•Fibres and connectors
sufficient rad hardness
trackers require miniature connectors
care with handling compared to electrical
[email protected]
www.hep.ph.ic.ac.uk/~hallg/
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November 2001
CMS Tracker analogue optical links
•Edge emitting 1.3µm InGaAsP MQW laser diodes
miniature devices required
single mode fibre
Laser die
~50mW/256 detector channels
Si-submount
PIN photodiode
Fibre
Si-submount
2 mm
1.5 mm
Tx
0.8
2.5
input
output
0.7
Fibre
1.5 mm
0.5
1.5
0.4
1.0
0.3
0.2
0.5
5 ns
0.1
same components for digital control
BER << 10-12 easily achievable
20 ns
5 ns
0.0
0.0
-0.1
0
5
10
15
20
25
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35
40
45
-0.5
50
Time [ns]
[email protected]
www.hep.ph.ic.ac.uk/~hallg/
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November 2001
Vout [V]
Rx
Vin / VFull Scale
2 mm
2.0
0.6