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13 Readout Electronics
A First Look
28-Jan-2004
January 28, 2004 J. Pilcher2
Requirements
Digitize charge seen by each PMT Energy reconstruction
Provide timing of signal for each PMT Position reconstruction
Provide trigger for DAQ Physics triggers
Neutrinos (prompt EM energy, delayed neutron energy) Backgrounds (to study and subtract) Muons
Electronic calibration triggers (test pulses) Source/laser/LED calibration triggers Random triggers
January 28, 2004 J. Pilcher3
Comparisons KamLAND is important reference point
Same reaction channel Scintillator-based detector Recent design But much larger target volume
~20 times larger
KamLAND resolutions Energy
7.5% / Sqrt[E(MeV)] 2% 5.7% at 2 MeV Position
25cm 5 cm– timing resolution 2.0 ns RMS after charge correction
January 28, 2004 J. Pilcher4
KamLAND Electronics Berkeley Analog Waveform
Transient Digitizer (AWTD) For 1325 PMTs (32%
coverage) Sample every 1.5ns
For signals above 1/3 pe 3 gain ranges (0.5, 4, 20) Store analog samples in
switched capacitor arrays until trigger
128 samples deep (200 ns) 10-bit ADC
~15 bit dynamic range Converts 128 samples in 25s.
January 28, 2004 J. Pilcher5
Channel Response CharacteristicsSensitivity Full Scale
Charge pe Energy Charge pe Energy(cnts/pC) (cnts/pe) (cnts/KeV) (pC) (pe) (KeV)
High Gain 247 186 55.7 4.14 5.5 18.4
Medium Gain 49.4 37 11.1 20.7 27.5 91.8
Low Gain 6.18 4.6 1.39 166 220 734
0.752 pC/pe
300 pe/MeV
Readout Resolution
0.10
1.00
10.00
100.00
0.10 1.00 10.00 100.00 1000.00
Single PMT Energy (KeV)
Percentage Resolution
January 28, 2004 J. Pilcher6
KamLAND Signals128 samples of 1.5ns3 gain scales(most events just use 20X
scale)
Gain 1/2
Gain 4X
Gain 20X
January 28, 2004 J. Pilcher7
KamLAND Vertex Reconstruction Calibrate timing of individual
PMT channels with variable laser pulses at center of detector
Time offsets T vs Q
Measure performance for physics with sources along z-axis
January 28, 2004 J. Pilcher8
KamLAND Vertex Reconstruction Mean reconstructed
position depends on photon energy
Apply energy dependent correction
January 28, 2004 J. Pilcher9
KamLAND Energy Reconstruction Set gains of PMTs using LEDs Equalize 1 pe peaks to 184 counts
Must correct for variations in storage capacitors All signals converted to equivalent photoelectrons Convert to energy using calibration sources
January 28, 2004 J. Pilcher10
KamLAND Energy Reconstruction
January 28, 2004 J. Pilcher11
Fresh look at Readout Electronics Avoid ASICs if possible (local bias)
Long development time Not cost effective in small volume Do not profit from evolution of chips in the
commercial sector Main advantage size and possibly performance
and functionality Continued performance growth in commercial
ADCs and FPGAs (PLD) Popular building blocks for many applications
January 28, 2004 J. Pilcher12
Fresh look at Readout Electronics Does one need detailed pulse shape for E and t?
Pulse shape discrimination can resolve photons from neutrons
Depends on scintillator Some exhibit this property and some do not May depend on light collection from target
– Reflections could obscure the effect
Much simpler if one can do shaping of input signal Output amplitude proportional to input charge Can be done with passive elements (no noise
added)
January 28, 2004 J. Pilcher13
ATLAS TileCal Approach For ATLAS TileCal 20 ns PMT signals converted
into 50-ns-wide standard shape Amplitude proportional to input charge Slower signal can be handled by commercial
ADCs (+40 megasamples per second) Analysis process fits shape to extract amplitude
and time
January 28, 2004 J. Pilcher14
Performance of TileCal System
Time reconstruction is excellentamplitude independent
January 28, 2004 J. Pilcher15
Alternatives Use LBNL AWTD
Likely if they join the collaboration Possibly an updated version
Build a system based on a flash ADC Eg. Maxim MAX1151
8 bit flash 750 MHz (sample every 1.3 ns) Power 5.5W each
Need 3 per PMT for dynamic range Use 40 MHz “system” clock à la LHC
Easy to distribute on optical fiber if LHC hardware used Generate local vernier clock synced to system clock Tale 16 samples for every 25 ns period of system
January 28, 2004 J. Pilcher16
Alternatives Build integrating system as in TileCal
The next steps Test LHC system reading out scintillator test cell Look at pulse shape discrimination with test cell Continue to think about electronics
Trigger– Can it be derived from digital data, thereby avoiding a second
signal branch
Consult with Harold