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Multi-time-over-threshold technique for photomultiplier signal processing
Characterisation of the SCOTT ASIC
S. Ferry1, F. Guilloux2
CEA Saclay, Irfu
and E. Delagnes2, F. Louis2, E. Monmarthe2, J-P. Schuller1, Th.Stolarczyk1, B. Vallage1, on behalf of the KM3NeT consortium3
1IRFU/SPP, 91191 Gif/Yvette, France2 IRFU/SEDI, 91191 Gif/Yvette, France3 Supported by the European Commission through FP6 and FP7
KM3NeT
• Now in preparatory phase (FP7)
• A European deep-sea research infrastructure for a neutrino telescope – Mediterranean Sea– Instrumented volume
5 km3
– 300 detection units– 12000 photo-detectors
• Cherenkov light detection– Upward – Downward cosmic – Optical background (100 Hz / cm-2)
40K decay in water
Bioluminescence
Mainly single photon signals
• All data to shore– On shore computer farm
2Sophie Ferry - NDIP11 - Characterisation of SCOTT
Front end requirements (from CDR)
• Time resolution (PMT+FE) < 2 ns at 1 pe (RMS)
• Charge dynamic range : 100 pe / 25 ns– Charge estimation
• Two-hit time separation < 25ns
SCOTT ASIC
3Sophie Ferry - NDIP11 - Characterisation of SCOTT
SCOTT concept
• Time and Amplitude Sampling– “wave-form”-like image of
the pulse
• Master Clock 50 MHz– 16 bit Time stamp
• 1.25 ns sampling
• 16 independent channels– Dynamic range : 0- 3V– 10 bit adjustable thresholds
• Auto-triggered– Each threshold can be a
trigger– Handling several PMTs e.g.:
2 PMTs x 8 thresholds
16 PMTs x 1 threshold
Sophie Ferry - NDIP11 - Characterisation of SCOTT 4
Analogue input
Analogue switchesInternal sharing of
signals
10 bit DACAMS BiCMos
0.35mProgrammable
thresholds LSB<3mV
DiscriminatorAnalogue to digital
convertor
SCOTT architecture
Sophie Ferry - NDIP11 - Characterisation of SCOTT
5x16 channels
SOC
Circular sampling memory
Delay locked loop (DLL)
All channels are synchronous
Circular digital memory
2 memory banks (MB)1MB = 1 time slice =20 ns
No dead time
16 bit coarse time counter
LSB = 20 ns
Time step TCK
/16
Ts
= 1.25ns (~ 800MHz)
SCOTT architecture
Sophie Ferry - NDIP11 - Characterisation of SCOTT
6x16 channels
SOC
SCOTT architecture
Sophie Ferry - NDIP11 - Characterisation of SCOTT
7x16 channels
SOC
FIFOAuto-triggered
Logical or channel triggered
Size32 time slices
640 ns continuous wave-
form
Data loss <1‰ for 200 kHits/s
Double portFck
sample ≠Fck
readoutReadout driven by System-on-Chip
Selective readoutData reduction
Scott output example
Sophie Ferry - NDIP11 - Characterisation of SCOTT
8
11280
0000000000000111000000000000001100000000000000010000000000000001
11281
11111111000000001111111000000000111111100000000011111100000000001111110000000000111111000000000011111000000000000111000000000000
Am
plitu
de
Time
20 ns
1.25 ns
Coarse Time stamp11283
0100000001111100
The SCOTT Opera
•
Act I : Determination of thresholds– Which values for how many thresholds ?
•
Act II : Charge
•
Act III: Timing– Correction of the walk effect– SCOTT Intrinsic timing accuracy
9Sophie Ferry - NDIP11 - Characterisation of SCOTT
ACT I THRESHOLD DETERMINATION
ActorsPMT : Antares 10’’ Gain=3·107
1 pe
50mV 5pC
LED : flashes at 1pe up to 70peOscilloscope : F=2.5GHz Bandwidth=500MHz
Sophie Ferry - NDIP11 - Characterisation of SCOTT
10
11
Tpeak
Sophie Ferry - NDIP11 - Characterisation of SCOTT
Performances verified with SCOTT
ACT II CHARGE RESOLUTION
ActorsPMT : Antares 10’’ gain=3.107
1pe
50mV 5pC
LED : flashes at 1pe and 11peSCOTT : 5 thresholds
Sophie Ferry - NDIP11 - Characterisation of SCOTT
12
• Integration of FRED : needs CPU time• Alternative based on Time-Over-Thresholds (TOT)
– Upper (Q+ ) and lower(Q- ) area under the thresholds
• Q
(Q+ + Q- ) / FQ– FQ depends on
the last threshold reached
the threshold values
requires calibration
Q+ Q-
13Sophie Ferry - NDIP11 - Characterisation of SCOTT
Charge resolution from TOTs
14
Charge 1pe
Mean=5pCRMS =2pC = 40%(PMT charge resolution
35%)
SCOTT + TOT enable charge reconstruction with good accuracy
Sophie Ferry - NDIP11 - Characterisation of SCOTT
ACT III TIMING RESOLUTION Scene 1 : Pulse time resolution
Sophie Ferry - NDIP11 - Characterisation of SCOTT
15
ActorsPMT : Antares 10’’ gain=3.107
1pe
50mV 5pC
LED : flashes at 1pe and 11peSCOTT : PMT 5 thresholds
LED trigger 1 threshold
Pulse time reconstruction
Walk effect- Threshold crossing time
depends on the charge- Peak time Tpeak unchanged
Sophie Ferry - NDIP11 - Characterisation of SCOTT 16
residuals
1st
thres.
TOT[i] (ns)
Tpea
k-T 0
[i]
All thresholds
Tpeak and Walk correction with SCOTT
• T1/3 -TLEDT1/3 =crossing time of the 1st
threshold
• Tpeak - TLED
Sophie Ferry - NDIP11 - Characterisation of SCOTT 17
(11+1)pe Nentr 1852RMS 1.5
1pe11pe
11+1pe
(11+1)pe Nentr 1852RMS 2.5
1pe11pe
11+1pe
TTSPMT
1.3 ns
Time resolution = 1.5 nsNo charge estimate needed
ACT III TIMING RESOLUTION Scene 2 : SCOTT Intrinsic timing accuracy
ActorsGenerator: HP 81110A 330MHz
SCOTT
Sophie Ferry - NDIP11 - Characterisation of SCOTT
18
SCOTT intrinsic timing
• Generated Pulse– 120mV height– 1kHz
• SCOTT: 6 thresholds15% 35% 50% 70% 85% 90%
Sophie Ferry - NDIP11 - Characterisation of SCOTT 19
00000000111111110000000000000111
11111111111111111111111111111111000111111111111100000000111111110000000000000001
111111111111111111111111111111111111111111111111111111111111111111111111111111110111111111111111
• Consider all possible time between crossing times for every couple of thresholds
(ns)
SCOTT intrinsic time resolution 0.8ns
Conclusion
20Sophie Ferry - NDIP11 - Characterisation of SCOTT
The End
Sophie Ferry - NDIP11 - Characterisation of SCOTT
21
PM
T
SCOTT architecture
• Analogue input
Analogue switchesInternal sharing of signals
10 bit DACAMS BiCMos 0.35m
Programmable thresholds LSB<3mV
DiscriminatorAnalogue to digital
convertor
• FIFO and zero suppressAuto-triggeredLogical or channel
triggered
Size32 time slices
640 ns continuous wave- form
Data loss <1‰ for 200 kHits/s
Double portFck sample ≠Fck readout
Readout driven by System-on-Chip
Selective readoutData reductionSophie Ferry - NDIP11 - Characterisation of SCOTT 22
• Fast memory samplingDelay locked loop
(DLL)All channels are synchronous
Circular digital memory2 memory banks (MB)
1MB = 1 time slice =20 nsNo dead time
16 bit coarse time counter
LSB = 20 ns
Time step TCK /16
Ts = 1.25ns (~ 800MHz)
1channel
FRED
23
Apeak
Tpeak
tR
Sophie Ferry - NDIP11 - Characterisation of SCOTT
Tpeak residuals
Sophie Ferry - NDIP11 - Characterisation 24
Apeak
Tpeak
tR
Test bench
Sophie Ferry - NDIP11 - Characterisation of SCOTT
25
PMT
HTAnode
Diff
LED
Black Box
PMT
HTAnode
oscilloscope
Diff
LED
Black Box
SCOTT
Generator
PMT
HTAnode
Diff
LED
Black Box
Generated pulse viewed with SCOTT
Sophie Ferry - NDIP11 - Characterisation of SCOTT
26
30164
00000000111111110000000000000111
30165
11111111111111111111111111111111000111111111111100000000111111110000000000000001
30166
111111111111111111111111111111111111111111111111111111111111111111111111111111110111111111111111
30167
111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111000
30168
11111111111111111111111111111111111111111111100011111110000000001000000000000000
30169
1111111110000011100000000000
Am
plitude
Time
20 ns
1.25 ns
PMT characterisation
• PMT + Oscilloscope
Sophie Ferry - NDIP11 - Characterisation 27
PMT
HTAnode
oscilloscope
Diff
Black Box
Define the 1PE 50 mV 5.4 pC
Amplitude max.
Charge
Amplitude with FRED & SCOTT
28Sophie Ferry - NDIP11 - Characterisation of SCOTT
T1/3 versus charge
• T1/3PE versus charge
29Sophie Ferry - NDIP11 - Characterisation of SCOTT
1PE and 11PE
Tpeak versus charge
• Tpeak versus charge
30Sophie Ferry - NDIP11 - Characterisation of SCOTT
1PE and 11PE
Sophie Ferry - NDIP11 - Characterisation of SCOTT31
Charge 11peCharge 1pe
Charge resolution with FRED + SCOTT
Mean=70pC RMS=22pC: 32%
Mean=5pC RMS=2pC: 37%
SCOTT + Pulse fit enable charge reconstruction without introducing further error
SCOTT data set
32Sophie Ferry - NDIP11 - Characterisation of SCOTT
• 1 + 11 pe data sets
0 1/3 2/3 1 4/3 5/3 2 3 8 pe
Analogue to digital@ SCOTT
Sophie Ferry - NDIP11 - Characterisation 33
Front End
Asic
System on
Chip
Analogue
Signal
Digital
data
Ethernet TCP/IP
data link
Shore