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A proposal of new simple system for testing a large number of MPPC
for the R&D phase of GLD calorimeter
2007/Feb/6
ACFA ILC Workshop
ICEPP , University of Tokyo
Hidetoshi OTONO
On behalf of the GLD calorimeter group
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Summary as Contents
Improvement points;-HardwareDeveloped a serializer (with optical relay) in order to reduce the number of expensive devices such as amplifiers and ADCs.-SoftwareSimplification of measurement method for basic properties; A way to simultaneously evaluate the
• dark noise rate• noise rate due to cross-talk (double pulse height) • gain of each MPPC .
of each MPPCs.
A large number of MPPCs are made in coming years in R&D. Checking them would be required for sharing the task among many universities; thus simple, robust, cheap and precise system is preferable.
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• Several calorimeter beam tests with increasing number of MPPCs are expected before the real ILC experiment. • We have to check basic properties (gain, noise rate, etc.) of brand-new MPPCs in each phase of R&D.•The simple, robust and cheap measurement method is preferable.
MotivationN
um. o
f MP
PC
s
Time
1k10k
100k
10M
Exp
erim
ent
R&D Period
Now
In near future, we would hopefullytest a prototype with orderof 100K MPPCs.
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Hardware : A development of signal serializer in order to reducethe number of expensive amplifiers and so on.
•Present method•A proposal of new method
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Issue of Present Method
MPPC
MPPC
MPPC
MPPC
Control PCHV
RS232C Present method uses parallel AMPs and ADCmodules.
Sequential process
Modules
AMP
AMP
AMP
AMPAMP
Multi-plexer Module
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Our Method
MPPC
MPPC relayOn
MPPC relayOFF
MPPC relayOFF
DC Supply
AMP modules
relayOFF
Measurementtarget
relayOFF
Control PCHV
RS232C
For this purposeWe have chosen optical relay.
About 5$
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Picture of the Circuit with Relay
Supply voltage for a relay
AMP
OFF OFF OFF ON
Supply voltage for a relay
MPPC output before a relay
MPPC output after a relay
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Requirement and Choice of Relay
relayOFF
relayOn
High isolation is required.
Low insertion loss is required.
Isolation (how well the pulse can be stopped when a relay OFF)
Insertion loss (how well the pulse can be passed when a relay ON)
10ns
?
?Isolation Insertion loss
1GHz
Isol
atio
n
Inse
rtio
n lo
ss
GOOD GOOD
30dB
10dB
0.6dB
0.3dB
1GHz100MHz100MHz
Orange’s propertiesbetween
100MHz ~ 1GHz
Isolation:10dB~30dBInsertion loss:0.3dB~0.6dB
[dB][dB]
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The effects of serializer on 10 samples
%10
Noise rate Noise rate due to Cross-talk
Gain
No relay [10^5]No relay [kHz]
With
rel
ay
[kH
z]
With
rel
ay
[kH
z]
With
rel
ay[
10
^5]
No relay [kHz]
There is no effect on noise rate and Cross-talk rate.Gain measurement with a relay is shifted a few percents, because of insertion loss →Correction is needed for gain measurement.
Noise rate and cross-talk rate spreads are about 10%,gain spread is 3%, due to large temperature variation.
A few %
%10 %10%3
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Plan
• The relay elements is quite effective in reducing the number of AMP and costs.
• Our 4ch circuit is still noisy, we need more
improvement.
• We are going to make a circuit with many relays.
• In parallel, we are searching another candidate for serializer.
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Software : We applied MPPC’s photon counting capabilities to simplify and the measurement of noise rate, cross-talk rate and gain.Moreover we raise the precision of measurement.
•Present method •A proposal of new method
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Present Measurement
LED on Gain
measurement
LED off
Threshold searching
Adjusting threshold for noise rateScaler counting for
Noise rate measurement
Adapting threshold for noise rate
(double pulse height)
Scaler counting forNoise rate measurement (double pulse height) Setting MPPC
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A proposal of new method
Change MPPC •Using dark noise for gain measurement•Threshold is fixed for noise rate
Taking ADC histogram OFFLINE analysis
•Noise rate•Noise rate (double pulse height)•Gain
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Our Circuit
MPPCMPPC
Dark Box
CAMAC
AMP
ChargeADC
CCNET
x 63
Scaler
Disc.
G.G
40ns gate
Clock
Outputregister
NIM
Disc.
vetolatch
x 10
The number of MPPCs will be increasing .
AMPrelayOn
DC Supply
Control PCHVRS232C
latch
Coin.
For the measurement of DAQ dead-time
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Our Method
GAIN
Channel
Num
. of e
vent Gate = 40ns
Noise rate(to be corrected
for DAQ dead time)Noise rate (double pulse height)
(to be correctedfor DAQ dead time)
Accidental coincidence rate of Noise is negligible.So the second peak is due to Cross-talk.
THRESHOLD
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Results
Bias Voltage
Bias Voltage
Bias Voltage
Noi
se r
ate
[kH
z]
Noi
se r
ate
[kH
z]
Gai
n [1
0^5]
• OURS• HPK
• OURS• HPK • OURS
• HPK
Noise rate Noise rate (double pulse hight)
Gain We compared our measurement with HPK data
•Noise rate and Gain is good correlation with HPKdata.•Difference can be seen for noise rate (double pulse height) → We are studying now.
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The Picture of Pulses
We show several pulses which we are studying now.
• Very closing pulses
• Curious pulses like discharge whose reason is completely unknown.
We took all pictures at 78.8V which is typical voltage for MPPC uses and they can be frequently shown .
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40ns
40ns
40ns
40ns
Very closing pulses
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Curious Pulses40ns
40ns
40ns
40ns
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Plans• Our method can be use for very closing pulses, and ours is more precise than present method.
• Accidental coincidence of noises is negligible at 100kHz noise rate, thus the closing pulses can’t explain the difference between measurement method.
• We guess that the closing pulses are due to cross-talk, though cross-talk induces ONLY the double pulse height output by present view. we are studying now.
• The origin of curious pulses is unknown, thus we are studying too.
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Summary
A large number of MPPCs are made in coming years in R&D. Checking them would be required for sharing the task among many universities; thus simple, robust,
cheap and precise system is preferable.
Our system is suitable for this purpose.
Improvement points;-Hardware Developed a serializer (with optical relay) in order to reduce the number of expensive device such as amplifiers and ADCs-Software Simplification of measurement method for basic properties; a way to simultaneously evaluate the dark noise rate, noise rate (double pulse height) and gain .
22
backup
23
Result (cont’d)
• OURS• PRESENT• HPK
Noise rate due to cross-talk
A significant differencecan be seen .The difference is about2 times.
Comparison with the resultof the same MPPC by present system
at another university
It’s our guess that the reason is understanding of cross-talk.
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Our Idea of Cross-talk
MPPC signalMPPC signal MPPC signal
Present idea Our idea
OR
MPPC outputs two types of pulse due to cross-talk; two times pulse height of normal noise and
double closed normal noise
The present method judges the latter as single normal noise
(c.f)normal noise
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A Candidate of Difference between Measurement Methods
MPPC signal
Disc. out
Present measurement method
Our measurement methodMPPC signal
ADC date
THR
scaler
ADC
2 noises
3 noises
Accidental coincidence rate of Noise is negligible.These can’t perfectly explain the difference.
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Typical Pulse
DarkBlue : raw pulseLightBlue : pulse via ONrelayPink : pulse via OFFrelay
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Gain Measurement Method Test
Gain
Gain(10^5)
Measurement with light source = 2.75 (10^5)
Measurement without light source = 2.7 + 0.07 (10^5)_
We checked 10 MPPCs
Thus we decide to use Dark noise for Gain.
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•30oC•25oC•20oC•15oC•10oC•0oC•-20oC
• 30 oC• 25 oC• 20 oC• 15 oC• 10 oC• 0 oC• -20 oC
1p
.e r
ate
Dependence on temperature