Transcript Document

Km3net meeting
Pylos, 16/4/07
S. Loucatos
DAPNIA, CEA-Sacaly
Front End Electronics
for the KM3NET Design Study
F. Guilloux*, J. Aublin, E. Delagnes,
F. Druillole, H. Le Provost,
S. Loucatos, J.-P. Schuller
DAPNIA-CEA-Saclay, APC
*[email protected]
CEA DSM Dapnia Sédi
Antares Front End (VFE) sum up
• Antares readout electronics
Ethernet
Network
Optical Module
Analog Ring Sampler
ARS Board
DAQ Board
• VFE requirements
•
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First Level Functionalities:
–
– Discriminate signals coming from the PMT.
– Measure their arrival time (0.5 ns rms precision). –
– Measure their charge.
–
– Bufferize and Derandomize the event flow.
Convert charge & time in digital data.
Format the events & serialize them
toward the DAQ board.
Oscilloscope mode.
•
2nd Level Functionalities:
– Rate Monitor + rate alarm.
– Filter by L1 and L2 (historical reason).
– Test Led generator …
•
All this for a reasonable power consumption and a low cost.
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Antares Front End (VFE) sum up
• Solutions developed in the Analog Ring Sampler ASIC
WaveForm : 128 memory cells
Sam
plingcontrol
SPE Charge
Integrator +
Time to Voltage
Converter
ADC
W
aveform modecontrol
T
ime ref.
clock
Dyn. 2
W
aveformmode
4*128memorycells
(ARS0)
Dyn. 1
Anode
Pulse Shape
Discriminator
SPE mode
Charge integrator
SPEmodePipeline
A
nalogm
emory cells
SPE mode
TVC
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+
C
omp.
ARS feedback
• Strength and weakness
+
• Time precision : 500ps rms
• Measure Charge of SPE without a
delay added to signal path
• Waveform :
• Too many functionalities and
parameters  hard to test
• Asic mainly asynchronous  hard to
simulate
• Two ASICs per OM (to minimize dead
time)  Should be done by one
- Fast sampling : 640MHz (up to
1GHz)
- 128 memories depth for 3
amplitudes
- The AMS 0.8µm is not available
any more
PMT output
1 GHz sampling
700 kHz A-D conversion
The ARS reaches expected performances but it is too complicated : the
architecture could be improved to make it simpler
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KM3NET conservative solution:
•
Reuse of Antares development, updated in order to fit to KM3NET
specific requirements:
Antares updated requirements
– OM  ASIC  DAQ Ethernet network
– “Input” specifications (Conceptual Design 1 & 2 from WP4)
• PMT electrical signal characteristics : 10’’ from Antares
– Amplitude : typically a few tens of mV per PE
– SPE Pulse time: all the signal is included in a window of 20ns
• Reference clock frequency : few tens of MHz
• Slow control protocol
– Physic requirements
•
•
•
•
•
Measure charge with DQ/Q < 10%
Measure arrival times with 0.5ns rms precision
Input dynamic range~ up to 100 pe
Input rate : up to 200kHz in average (SPE), max. 500kHz during 1s
Discriminate multi-muon bundles
Km3Net requirements
– Scale effects  Consumption, Design simplifications
– Cost reduction  Design Optimizations
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New VFE Asic: Submarine Cherenkov rAdiated Light Electronic
(SCALE)
8 bits
SPE memory
SPE memory
SPE memory
SPE memory
SPE memory
SPE memory
SPE memory
SPE memory
ADC
8 Ch
Dg
DLL DLL DLL DLL DLL DLL DLL DLL
Anode
PSD
L0, WF
Infos
L0
L0 accepted
WF valid …
8 bits
Switch Array Capacitors
16*32 = 512
Delay Locked Loop
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ADC
32 Ch
Dg
Scale : key points
•
The memory Cell
– Ring memories keep the past of the signal  No need of external delay line
– Fine Time and charge are extracted from the same unit  Simplification
– Fine Time is extracted from a Delay Locked Loop
 No ADC needed to convert time information : it is naturally digital
 Easy to calibrate : possible to reach ns precision from a 20MHz input
reference clock with few spread (feedback loop)
Clock
Trigger
DLL
Fine Time (~6 bits)
Signal IN
Signal OUT
Switch Capacitors Array
•
Multi-channels Wilkinson ADC
– 8 bits resolution, ~ 5MHz conversion frequency
•
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Architecture simplification
– One Asic up to 500kHz (SPE)  Queuing theory : probably 2 banks of 4
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memories
High level language Simulations
•
Simulations scheme
Shape discriminator
Bias
ADC
Digital
Control
8 memories
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Digital Fifo
Digital Mux
High level Simulation Results
–
–
–
–
–
Signal filtering
Dynamic range ~ 100 pe
Integrated charge error < 10%
Time resolution < 0.5ns rms
Digital output
• Charge : 10 bits
• Fine Time : 6 bits
• TimeStamp : 24 bits
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Transistor level simulations are in
progress
Other solution under study: Multi-threshold discriminator
•
Discrimination strategy
– Arrival time and TOT is given by several discriminators.
Input
Threshold1
Threshold2
 SPE and others signals are treated the same way : no need of waveform
 The electronics is simpler : minimal analog circuitry
– Is it possible to find the charge with enough accuracy knowing only the TOTs ?
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Experimental setup
ANTARES
Optical Module
LED triggered
by generator
pulses
Acquisition by
digital
oscilloscope
(2.5 GHz)
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Number of events (over 1000 events)
p.e. study
Histogram of Charge
Acquisition of 1000 pulses
without flasher with the LED
180
Trigger on p.e. background
120
Charge integration:
Q =  Vi x Dti. ,or better:
Simpson integral
Mu = 0.363
Sigma = 0.156
160
140
100
80
60
40
20
0
0
0.2
0.4
0.6
Charge (pVs)
Average track estimation
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0.8
1
Using the LED
Runs with
several LED
intensities
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Signal shape
0
Fit
(scaling with LED
intensity assumed)
0
-0,5
Charge = 6 SPE
-1
Amplitude in V
Amplitude in V
-0,2
-0,4
Charge = 12 SPE
-0,6
Fit
-1,5
-2
-2,5
Charge = 131 SPE
-0,8
-3
Charge = 35 SPE
-3,5
-1
-4
0
5
10
15
20
25
30
0
5
10
15
Time in ns
Time in ns
Fit with sum of 4 gaussians
or gamma distribution :
g (t )  a  t n  exp(b  t )
Fit on the average low amplitude signal then fit 1 parameter only
(normalization).
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20
25
30
Relation ToT-Charge
Threshold values
tested:
• Th= 1/3 PE
• Th = 2/3 PE
• Th = 1.5 PE
• Th = 5 PE
• Th = 10 PE
• Th= 20 PE
• Th = 40 PE
Fit: ToT = A + B* Ln( Charge / Charge 1p.e.)
Constants A et B to be determined for each threshold value
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Charge and time reconstruction
• Time is given by crossingof the first
threshold. “walk” effect, need of the amplitude or charge for correction.
•
Charge reconstruction: 3 methods
–
–
–
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Fit by a pulse form
TOT ~ Ln (Q)
Geometrical approximation
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Data quality
•
Dispersion of time of the LED emission
•
Oscilloscope window reduced in amplitude
Number of events (over 1000 events)
 Quantification noise >> electronic noise
Histogram of Peak time
90
Mu = 148
Sigma = 1.19
80
70
60
50
40
30
20
10
0
140
145
150
155
time (ns)
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160
165
170
Fit method
•
Hypothesis :
If all the photons are perfectly synchronous, the curve of the output of PMT is homothetic
to the SPE curve.
•
Méthod :
•
We fit the average curve of SPE by a parametrised curve (A0,T0)
•
We fit the pairs of points of threshold crossings by this parametrised curve
Charge reconstruction Error
Charge reconstruction Error
20
40
30
20
10
0
-10
-20
-30
-40
-50
-60
-70
-80
-90
-100
-110
-120
-130
-140
Error (%)
10
Error (%)
0
-10
Error (%)
-20
2/3pe
-30
<= Threshold
1.5pe
20
10
0
0
•
0.5
Conclusions:
–
–
–
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1
1.5
2
2.5
Charge/Charge SPE
3
3.5
4
4.5
5
7 Thresholds
4 Thresholds
5pe10pe
0
20
20pe
40pe<= Threshold
40
60
Charge/Charge SPE
Good charge reconstruction in the entire range (~ +/- 10% RMS)
Sensitive to the LED dispersion de la LED (but systematic deviation correctible)
Very sensitive to the number of thresholds
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80
100
120
Expected time dispersion
Photon arrival times in water (incl. Antares electronics DT)
The dispersion of the LED emission has some similarity with
Cerenkov data
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TOT method
•
Hypothesis :
–
TOT vs Charge
50
TOT ~ Ln (Q)
Time Resolution Oscillo.
40
Méthod :
30
TOT (ns)
•
–
For each threshold we
find points (A,B) such
that :
TOT = A + B * Ln(Q)
20
10
0
–
We use then the
inverse function
Threshold 13mV ~ 1/3 SPE
-10
0
2
4
6
8
10
12
Charge/Charge SPE
Conclusions :
–
–
–
Histogram of the RMS Error
40
Sensitive to the fit for
(A, B)
Sensitive to double
non simultaneous
pulses!
After strong filtering
and using the
correction, then
approach 10%
Error (%)
•
30
20
10
0
-10
-20
1.5pe 5pe
-30
0
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10
10pe
20pe
20
30
40pe
40
50
Charge/Charge SPE
60
70
80
90
100
Geometrical method
•
Amplitude
Hypothesis :
–
•
The simplest method to compute
Seuil 3
the charge : the area under the
curve
Method :
–
Seuil 2
Linear interpolation between
points
Interpolation TOT1 = A+B*Ln(Q)
for the last threshold
–
TOT1
Seuil 1
Temps
25
20
15
•
Error (%)
10
5
–
0
-5
–
-10
-15
-20
5pe
10pe
20pe
40pe
<= Threshold
-25
0
10
20
30
40
50
Charge / Charge SPE
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Conclusions:
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60
70
80
90
100
Very efficient for high
charges
Sensitive to the start and
exponential decrease at
small charge (few points)
Time reconstruction + walk correction
•
Hypothesis :
– Why go through the charge in order to correct time ?
•
Méthod :
– For each threshold, we find points (A,B) such that : Tpic = A*TOT² +
B*TOT+C+Tinit
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Time reconstruction + walk correction
•
Resuts :
– With 8 thresholds : error
on Tpic ~ 300ps RMS
– With 3 thresholds : error
on Tpic ~ 800ps (sigma),
even with our digitisation
error. But: double pulse
recognition difficult with 3
thresholds
•
Conclusion :
– With TOT exact
computation (error of
800ps) of arrival time
– With thresholds,
approximation of number
of photons
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Solution for TOT
•
Schémas 1 :
Analogue
Digital
FPGA
• Time coding
•Data compression
Zero suppression
Charge and Time
Simulation Test on
Virtex V  500MHz
1ns 1ns
+ Simplicity : few components
- Communication Discri – FPGA high frequency
- Time precision : 1ns  Fsampl ≥1 GHz
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Solution for TOT
•
Schémas 2 :
Analogue
Digital
Clock
FPGA
n
• Time coding
…
…
…
• Data
compression
n
Data
Discri.
Sampling
Data in
parallel
+ Synchronous
+ Communication Discri – FPGA medium frequency
- Volume of simultaneous data
…
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Backup
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VFE principle
• Limited functionalities
–
–
–
–
–
–
–
Discriminate signals coming from the PMT.
Measure their time (~ 0.5 ns rms precision).
Measure their charge.
Bufferize and Derandomize the event flow.
Convert charge & time in digital data.
Format the events & serialize them toward the
DAQ board.
An Oscilloscope mode (Wave Form)
–
–
–
Rate Monitor + rate alarm.
Test Led generator.
…
• Discrimination principle
• Electrical Shape from PMT,
in case of single photon, is
known : Only arrival time (T0)
and charge is needed.
• In order to recognize
patterns from multi-muon
bundles, TOT larger than
T0+T1 is treated as a
Waveform
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Amplitude
T0 + few ns
T0
Charge
WaveForm
Threshold
T0
T0 + T1
Time
Résumé :
Q > 10 PE
10 > Q > 2
Amplitude
Amplitude
Temps
• Bonne approximation de
la charge, quelque soit la
méthode.
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Amplitude
Temps
• Fit ne voit pas le 2e pulse
• TOT surestime ou sousestime la charge
• Géo. bonne
approximation
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2>Q
Temps
• Fit et TOT: bonne
approximation si pas de
2e pulse sous le 1er seuil
• Géo. : pas
d’interpolation possible
Future developments
•
•
Complete schematic simulations
Scale Prototype : include in a new PMT readout scheme
DAQ Board
ARS Board
– Board number
reduction
– Component number
reduction
 System On Chip
•
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VFE
VFE
PMT
control
TOT option under study
CEA DSM Dapnia Sédi
SoC
Objectives :
– VFE
– Antares compatibility
– Tests in laboratory
– OM integration (in the sphere)
– Test in situ