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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/6ACFA ILC Workshop

ICEPP , University of TokyoHidetoshi 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

Expe

rimen

t

R&D PeriodNow

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

ＭＰＰＣＭＰＰＣＭＰＰＣＭＰＰＣ

Control PCHV

RS232C Present method uses parallel AMPs and ADCmodules.

Sequential process

Modules

AMP

AMP

AMP

AMPAMPMulti-plexer Module

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Our Method

ＭＰＰＣＭＰＰＣ 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 ONSupply 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

rtion

loss

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

rela

y [k

Hz]

With

rela

y [k

Hz]

With

rela

y[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 r

elays.• In parallel, we are searching another candi

date 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

measurementLED 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

MPPC

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 MethodGAIN

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 ra

te [k

Hz]

Noi

se ra

te [k

Hz]

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 .

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backup

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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 noiseThe 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 ra

te

Dependence on temperature