W. Shen arXiv:0911.1566v1 [physics.ins-det] 8 Nov …azusa.shinshu-u.ac.jp/~coterra/EBUreferences/Spiroc/0911...y/Pulsar, MEPh tical iden to the devices used in AHCAL test b eam op

arX

iv:0

911.

1566

v1 [

phys

ics.

ins-

det]

8 N

ov 2

009

Overview of Studies on the

SPIROC Chip Chara terisation

R. Fabbri

1, B. Lutz

1, W. Shen

2

1DESY, Hamburg

2University of Heidelberg

September 26, 2013

Contents

1 Introdu tion 2

2 SPIROC ASIC Des ription and Properties 2

3 Test-Ben h Des ription 4

4 Ele tri al Noise Investigation 5

5 ENC and Input Dete tor Capa itan e 8

6 Pedestals Uniformity 11

7 Trigger Dis riminator and E ien y 11

8 Trigger Time Walk and Jitter 14

9 SiPM Voltage Adjustment 17

10 Low Gain - High Gain Coupling 20

11 Cross Talk between Input Channels 21

12 Tra k and Hold Swit h 22

13 Dynami Range, Linearity, and Gain of the ASIC 23

14 Amplitude Dependen e on Shaping Time 28

15 SiPM Single-Pixel Spe tra 30

16 Towards Real Data Taking Conditions 34

17 Con lusions 39

1

http://arxiv.org/abs/0911.1566v1

1 Introdu tion

The requirements imposed by the high pre ision physi s forseen at the Interna-

tional Linear Collider (ILC) set high demands on alorimetry. The ambitious

required jet energy resolution of σE/E ≈ 0.3/√

E [1 ould be a hieved by om-

bining the potentials of the parti le ow approa h [1 with extremely segmented

(in both transverse and longitudinal dire tions) ele tro-magneti (ECAL) and

hadroni (HCAL) alorimeters.

The ECAL design is based on a Si-W sampling stru ture with sensitive

sili on pads of 1 m

2surfa e. The prototype will onsist of approximately

10000 hannels. A group of the CALICE ollaboration has developed the analog

option for the hadroni alorimeter (AHCAL) based on a sampling stru ture

with s intillating tiles (of smallest size 3x3x0.5 m

3) individually readout by

Sili on Photo-Multiplier (SiPM) mounted on ea h tile.

The SiPM is a pixelated avalan he photo-diode operated in limited Geiger

mode. The dete tor surfa e typi ally of few mm

2is divided into hundreds to

thousands pixels. The analog output is obtained by adding the response of all

pixels ring as independent digital ounters. SiPMs are operated at 2-3 volts

overvoltage. Given an internal pixel apa itan e Cpixel of typi ally 50 fF, the

harge olle ted for one photoele tron signal is approximately 1.2 pC (equivalent

to ≈ 7.5 · 105ele trons). The SiPM oers a very fast response with a typi al

rise time of 3-5 ns. The dynami range is determined by the nite number of

pixels and rea hes ≈ 92 pC.

In order to test the feasibility of the parti le ow approa h prototypes of

both ECAL and HCAL are being built by the CALICE ollaboration and being

tested in a ombined test beam experiment. To meet the needs of the analog

HCAL prototype it was de ided to adapt the design developed for the ECAL

front-end ele troni s to read the SiPM signal. This ILC-SiPM ASIC has been

used during the test-beam runs at CERN and FNAL in 2006-07 and 2008-09,

respe tively. SPIROC is an evolution of the ILC-SiPM to be used for the next

generation of ILC AHCAL prototype. In the following the main features of the

new ASIC, version SPIROC 1B, proposed for the readout are des ribed and its

properties analysed. More spe i ately, the results on the analogue part of the

hip are presented in this work. When reading out signals from photon dete tors,

SiPMs from MEPhy/Pulsar, identi al to the devi es used in the AHCAL test

beam operations, were used. These SiPMs have a 1x1 mm

2surfa e divided into

1156 pixels.

The on going investigation of the digital omponent of the ASIC, imple-

mented in the version SPIROC 2, will be presented in a separate future note.

2 SPIROC ASIC Des ription and Properties

The SPIROC hip is a dedi ated very front-end ele troni s for an ILC prototype

hadroni alorimeter with sili on photomultiplier readout. This ASIC has been

designed and developed by OMEGA at Orsay [2.

2

Figure 1: SPIROC: one analog hannel stru ture.

SPIROC was submitted in Fall 2007 and being tested sin e then. It em-

beds utting edge features that full ILC nal dete tor requirements. It has

been realised using AMS 0.35 µm SiGe te hnology, and developed to mat h

the requirements of large dynami range, low noise, low power onsumption,

high pre ision and large number of readout hannels needed. SPIROC is an

auto-triggered, bi-gain, 36- hannel ASIC whi h allows to measure on ea h han-

nel the harge from one to 2000 photoele trons and the signal timing with a

100 ps a ura y TDC. The integrated ASIC omponents allow 16 sele table

pre-ampli ation gain fa tors (with output gain values from 3 to 100 mV/pC),

and seven CR(RC)

2shaping times from 25 to 175 ns. After shaping, the signal

is held at its maximum amplitude with a tra k and hold method. For ea h han-

nel, an analogue 16 slots memory array is used to store the time information

and the harge measurement, and a 12-bit Wilkinson ADC has been embed-

ded to digitise the analogue memory ontent (time and harge for the two gain

modes). The data are then stored in a 4 kbytes RAM. A very omplex digital

part has been integrated to manage all theses features and to transfer the data

to the data a quisition system. An adjustable 8-bit DAC (0-4.5 V) in the ASIC

allows individual adjustment of the SiPM forward voltage for ea h one of the

36 hannels.

A s hemati view of a single hannel of the ASIC hip is given in Fig. 1.

3

hold

ASICpulse generator

50Ω

−20dB

100 pF

STS DG 535

ADC module

CAEN V785N

gategenerator

bufferamplifier1x or 9x

VME CAEN 8002

Figure 2: Typi al test ben h set up for the ommissioning of the SPIROC hip

at DESY.

3 Test-Ben h Des ription

The hara terisation measurements of the SPIROC hip were performed at

DESY. The typi al set up of the test ben h is shown in Fig. 2. A digital

pulse voltage generator (STS DG535) provides a re tangular signal at 10 kHz

rate and with variable amplitude up to 4 V. Additionally, a 20 dB attenuator

(10 fa tor attenuation) is inserted in the signal line. To simulate a real urrent

signal from SiPMs, the generated squared signal is driven through a oupling

apa itor (C = 100 pF) and a resistor (R = 50 Ω) lo ated before the input han-nels in the SPIROC board, resulting in a hara teristi de ay time τ = 5 ns for

the urrent signal.

The signal is then inje ted in one of the 36 input hannels, and the pro essed

4

output signal an be measured either at the os illos ope (Tektronix TDS 3034B,

running at 300 MHz bandwidth with 2.5 Gs/s sampling rate) or dire tly via an

external ADC module (CAEN V 785N), a ommodated in a VME reate (CAEN

8002). The data a quisition is performed via a LINUX ma hine onne ted to

the VME rate. The pulse generator is also onne ted to the LINUX ma hine,

and is driven by s ripts, allowing, together with the a quisition, for automati ,

exible, and systemati measurements in a large parameters spa e using SHELL

s ripts. Via an USB onne tion the hip is driven by a LabView user interfa e

running under WINDOWS be ause the USB driver to steer the hip is not

available for LINUX systems. This restri ts the automation and exibility of

the measurements performing the s an of the ASIC related parameters. The

porting of this software to a LINUX platform is ongoing.

A buer amplier, built at DESY, was often used (before the ADC input

hannels) to improve the pre ision of the measurement, as in the noise studies.

4 Ele tri al Noise Investigation

The noise ae ting the pro essed signal out of the board was measured at dif-

ferent working onditions of the hip. Additional sour es an superimpose to

the hip noise during the measurement, as the USB- onne tion to the omputer

driving the board, the lo k on the board whi h handles the input/output om-

muni ations with the omputer, and the onne tions to the pulse generator for

the input and hold signals.

After dis onne ting these additional noise sour e from the board, the noise

was measured as the RMS of the analogue output signal. The dependen e of the

noise on the variable apa itan e in the preamplier stage of the hip is shown

in Fig. 3, for both high and low gain operation modes. The expe ted 1/Cgain

dependen e in the high gain mode is observed. The noise rea hes its asymptoti

value for the largest feedba k apa itan e investigated value. For the low gain

mode, where the ampli ation is one order smaller than for the high gain mode,

no dependen e is visible, being the noise dominated by the either the hip or the

experimental board (the noise from the external ADC module was measured to

be up to 0.1 mV).

The dependen e of the hip noise on the shaping time values is presented in

Fig. 4. An almost linear dependen e in the high gain mode is observed, while

for the low gain mode no dependen e is visible, similarly to what observed for

the dependen e on the feedba k apa itan e.

The uniformity of the noise in the SPIROC 36 input hannels was also in-

vestigated, and the result of the measurement is presented in Fig. 5, for the

hip operating in high gain mode, at 50 ns shaping time, and 400 fF variable

apa itan e in the pre-amplier stage. The measured noise is uniform within

fra tions of millivolts, well enough for the hip purposes. Although the upper

half of hannels appears to have a higher noise, this feature was not furtherly

investigated being the ee t negligible.

The largest ee t superimposed to the ele tri al noise is given by using the

5

[fF]gainC0 200 400 600 800 1000 1200 1400 1600

no

ise

(o

utp

ut R

MS

) [m

V]

0

0.2

0.4

0.6

0.8

1

1.2

1.4

High Gain

Low Gain

Figure 3: The hip noise is measured versus the variable apa itan e in the

preamplier stage, for 50 ns shaping time.

Shaping time [ns]0 20 40 60 80 100 120 140 160 180 200

no

ise

(o

utp

ut R

MS

) [m

V]

0

0.2

0.4

0.6

0.8

1

1.2

1.4

High Gain

Low Gain

Figure 4: The hip noise is measured versus the shaping time for 400 fF variable

apa itan e in the preamplier stage.

tra k and hold swit h to hold the pre-amplied and shaped signal at its peaking

amplitude. An in rease of the noise up to a fa tor 2-3 is observed in the output

signal, Fig. 6. With the used setup we ould not distinguish between an in rease

of the noise or of the sensitivity to the noise (due to the in reased bandwidth

6

Input channel0 5 10 15 20 25 30 35

no

ise

(o

utp

ut

RM

S)

[mV

]

0.39

0.4

0.41

0.42

0.43

0.44

0.45

0.46

High Gain mode

50 ns shaping time

400 fF variable capacitance

Figure 5: The noise is measured independently for all the 36 input hannels of

the hip in high gain mode.

Entries 100002

Mean 76.07

RMS 0.3972

Pedestal [mV]60 65 70 75 80 85 90 95

Yie

ld

0

2000

4000

6000

8000

10000 Entries 100002

Mean 76.07

RMS 0.3972

Entries 100000

Mean 75.39

RMS 0.9843

Entries 100000

Mean 75.39

RMS 0.9843

High Gain

Shaping time: 50 ns

Feedback capacitance: 400 fF

High Gain

Shaping time: 50 ns


High Gain

Shaping time: 50 ns


With T. & H.: Without T. & H.:

Figure 6: The hip pedestal and noise are measured in high gain mode for 50 ns

shaping time and 400 fF feedba k apa itan e. The distributions were obtained

separately while keeping the tra k and hold omponent swit hed on and o

(hat hed and lled histograms, separately). The USB onne tion to the driving

PC, and the internal lo k were left on during these measurements.

indu ed by the tra k and hold swit h). Instead, a negligible ee t is observed

by the swit hing on the internal lo k for input/output ommuni ation with an

external driving interfa e (via USB port), and by plugging the USB onne tor

7

Entries 100003Mean 75.68RMS 0.407

Pedestal [mV]73 74 75 76 77 78 79 80

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2000

4000

6000

8000

10000Entries 100003Mean 75.68RMS 0.407





High Gain

Shaping time: 50 ns


High Gain

Shaping time: 50 ns


High Gain

Shaping time: 50 ns


W/O Clock and USB:W/O Clock and W USB:

With Clock and USB:

Figure 7: The hip pedestal and noise are measured while keeping the tra k and

hold omponent swit hed o (lled histogram), and in sequen e plugging the

USB onne tor to the board and swit hing on the internal lo k (striped and

point histograms, separately).

into the board, Fig. 7. In normal data taking onditions the ASIC is supposed

to pro ess the in oming signals via the tra k and hold omponent swit hed on.

Therefore it is important also to measure its impa t on the measured noise

dependen e on the preamplier gain, Fig. 8. Consistently with what shown in

Fig. 6, an in rease of the noise up to approximately a fa tor 3 is observed at

Cgain = 1500 fF.

5 ENC and Input Dete tor Capa itan e

Sofar the ele tri al noise of the stand-alone ASIC was investigated, without any

input signal line onne ted to the board. Conne ting a SiPM to the readout

system is expe ted to in rease the noise, depending on the dete tor apa itan e.

In prin iple, a harge-sensitive preamplier would be favoured [5, providing

small sensitivity to hanges of the parasiti apa itan e at its input, as in the

ase of SiPMs whose apa itan e hanges with temperature. Nevertheless, in

order to over the large dynami range of SiPMs, a voltage-sensitive preamplier

was adopted for the hip. It is ru ial therefore to quantify the noise sensitivity

to an external variable apa itan e oupled via the onne ted dete tor.

Sin e the signal from the SiPM appears as ele tri harge, ele troni noise

will be quantied by giving its 'equivalent noise harge' (ENC), dened as the

input harge whi h would be ne essary to generate a signal equivalent in am-

plitude to the measured noise output of the ASIC. This value an be obtained

by normalising the noise to a referen e signal. As an example, the signal origi-

8

[fF]gainC0 200 400 600 800 1000 1200 1400 1600

no

ise

(o

utp

ut R

MS

) [m

V]

0.5

1.0

1.5

2.0

2.5

High GainHigh Gain

Figure 8: The hip noise is measured versus the variable apa itan e in the

preamplier stage keeping the tra k and hold omponent swit hed o. The hip

was operated in high mode at 50 ns shaping time.

nating from one photo-ele tron in the SiPM, and its orresponding output are

onsidered. Assuming a SiPM gain GSiPM of order 5 · 105would result in an

input harge Qin approximately of GSiPM · e = 80 fC. The orresponding out-

put signal Vout for the highest gain was found to be ≈ 7.6 mV (see Se . 16),

obtaining an ENC of order

ENC = VRMS ·Q1pxl

in

V 1pxlout

= VRMS ·80

7.6≈ VRMS · 10.5 [fC · mV −1]. (1)

Here VRMS is the average voltage noise level (in millivolt) appearing at the

output. Dividing it by the the ele tron harge e (in femto oulomb units) gives

the ENC in number of ele trons

ENC = VRMS ·10.5

1.6 · 10−4≈ VRMS · 7 · 104 [electrons · mV −1]. (2)

Using the external pulse generator, the output noise was measured and on-

verted in number of equivalent ele trons following the above formula (2). Dur-

ing the measurement, the oupling apa itan e value was varied to simulate the

hange of the SiPM internal apa itor. The results of two s ans performed in

sequen e, without any hange in the setup apart repla ing the apa itor, are

presented in Fig. 9, showing a noise VRMS in rease up to 20% in the range

0-100 pF, from 1.6 to 2.1 mV ( orresponding to an ENC variation from 9 ·104to

11.5·104ele trons). A ording to these measurements, the signal over noise ratio

a hievable by the SPIROC an be al ulated, ranging approximately between

4.7 and 3.6 assuming a SiPM of 5 · 105.

9

Input Coupling Capacitance [pF]0 20 40 60 80 100

Ou

tpu

t N

ois

e [m

V]

1.5

1.6

1.7

1.8

1.9

2.0

2.1

2.2

4x10 ]-E

qu

ival

ent

No

ise

Ch

arg

e [e

8.0

8.5

9.0

9.5

10.0

10.5

11.0

11.5

12.0

Input charge: 0.5 pC

HG shaping time: 50 ns

HG feedback capacitance: 100 fF










Figure 9: Equivalent noise harge measured while varying the oupling apa i-

tan e at the input signal line.


Output Noise [mV]1.5 1.6 1.7 1.8 1.9 2 2.1 2.2

Yie

ld

0

5

10

15

20

25

30

35

40

45




High GainInput charge: 0.5 pCShaping time: 50 nsFeedback capacitance: 100 fF




CC: 10 pF: CC: 100 pF:

Figure 10: Distribution of noise

measurement performed at two

dierent oupling apa itan e

values.

To verify that the observed non-reprodu ibility of the measurements is not

given by any feature of the ASIC, a series of measurements was taken in se-

quen e at a xed oupling apa itan e to simulate the dete tor apa itan e. No

additional hange in the experimental apparatus was introdu ed. The results

for two values of the oupling apa itan e, Fig. 10, shows a spread in the mea-

surement whi h is of the order of a fra tion of millivolt. This is well below the

maximum spread observed in the two onse utive s ans, thus suggesting a noise

sour e external to the ASIC, possibly due to the experimental setup.

The measurement of the oupling apa itan e dependen e of the ENC was

performed inje ting 0.5 pC into the ASIC (ex ept for the measurement at zero

apa itan e, when the line was dis onne ted from the board). To validate the

results it should be veried the reasonable assumption that the measured noise

10

Injected voltage [mV]1 2 3 4 5 6 7 8 9 10

no

ise (

Ou

tpu

t R

MS

) [m

V]

1.5

1.6

1.7

1.8

1.9

2

2.1

2.2

High Gain

Shaping time: 50 ns


High Gain

Shaping time: 50 ns


High Gain

Shaping time: 50 ns


CC: 100 pF

CC: 10 pF

Figure 11: The signal noise is measured for dierent values of the inje ted

voltage from the pulse sour e, and for two extreme values of the oupling

apa itan e (CC).

is not inuen ed by the amount of inje ted harge. A measurement of the

noise was taken at dierent values of inje ted harge, and for two values of the

oupling apa itan e, showing, as expe ted, no dependen e, Fig. 11.

6 Pedestals Uniformity

Pedestals were investigated for all the the 36 input hannels of the hip, to verifytheir uniformity, and are presented in Fig. 12, using the external ADC module.

Note that the mean values reported here are not the absolute pedestal values,

due to an oset introdu ed for onvenien e in the amplier before the ADC.

The measured spread of pedestals is about 2.3 mV, Fig. 13, a value slightly

larger than what reported in [2.

7 Trigger Dis riminator and E ien y

The hip is designed to operate in the so alled 'auto-trigger' mode. The input

signals are rst pre-amplied a ording to both low and high gain line settings.

In the high gain se tion a dedi ated 15 ns fast shaping line is also present in

parallel to the line to the analogue memory. There the signal enters a dis rimi-

nator with a threshold ommon to all 36 input lines, and a 120 ns wide trigger

is generated whenever the voltage in the line is above the threshold value set,

11

Channel number0 5 10 15 20 25 30 35

pe

de

sta

l (o

utp

ut

me

an

) [m

V]

50

60

70

80

90

100

High Gain mode

50 ns shaping time

400 fF variable capacitance

Figure 12: Pedestals measured for all the 36 input hannels of the hip, using

the external ADC module.

pedestal (output mean) [mV]60 65 70 75 80 85 90 95 100

Yie

ld

0

1

2

3

4

5

6

7Entries 36

Mean 84.15

RMS 2.302

High Gain

50 ns shaping time

400 fF variable capacitanceFigure 13: Pedestal distri-

bution for all the 36 input

hannels.

Fig. 1. The ommon threshold is tunable by a 10 bits DAC. On top of the

ommon threshold value, ea h hannel threshold an be individually tuned via

a 4-bit DAC.In normal ILC operations the generated trigger is forseen to subsequently

hold the pre-amplied signal, pro essed in the meanwhile by slower shapers, at

its amplitude peaking value. It is therefore ru ial to investigate the trigger

e ien y and homogeneity for the 36 hannels.

The alibration of the ommon DAC values was performed, and is shown in

Fig. 14. The threshold is found to range from 0.35 V up to 2.26 V. The residuals

12

DAC value0 200 400 600 800 1000

Mea

sure

d Vo

ltage

[V]

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

2

2.2 / ndf 2χ 8.41e-05 / 17

p0 0.001242± 2.262

p1 1.943e-06± -0.001864

/ ndf 2χ 8.41e-05 / 17

p0 0.001242± 2.262

p1 1.943e-06± -0.001864

DAC value0 200 400 600 800 1000R

esid

ual t

o Li

near

ity [m

V]

-10-8-6-4-202468

10

Figure 14: The alibration of the ommon signal threshold 10-bit DAC values

into volt units.

to linearity, found to be within few millivolts (a fra tion of a photon-ele tron

signal), are presented in the small insert panel.

After having performed the dis riminator DAC alibration, the trigger ef-

ien y an be investigated hannel by hannel. This is done using a built-in

pro edure in the LabView user interfa e. The program in reases the threshold

level in sequen e of DAC units, remains at a xed DAC value for 200 y les,

and ounts the number of triggers generated by the pedestal of the investigated

hannel. It provides thus a measurement of the trigger e ien y, whi h is pre-

sented in Fig. 15 for an inje ted harge of 100 fC, separately for ea h of the 36

Discriminator Threshold [mV]

Trigg

er Ef

ficien

cy %

0

20

40

60

80

100

1205 1210 1215 1220 1225 1230 1235

Figure 15: The trigger e ien y spread for all the 36 input hannels in the

ASIC, relative to an inje ted harge of 100 fC.

13

Time jitter

Trigger level

Pedestal

Figure 16: Examples of trigger time walk (left panel) and jitter (right panel).

hannels.

The in rease of the trigger ounting is smoothed by the noise amplitude in

the line, whi h was typi ally found to be around 2-3 mV during that spe i

measurement, and was obtained onsidering the threshold value variation needed

to in rease the trigger e ien y from 10% to 90%. Also, the maximum e ien y

is rea hed at threshold level values dierent from hannel to hannel, with a

spread of around 5 mV, resulting in a negligible pedestal spread between all

the 36 hannels. During forseen data taking operations, the observed spread

an, in prin iple, be ured tuning the dis riminator level hannel by hannel

using the forseen 4-bit threshold ner adjustment. At the moment, this feature

is not properly working in the released versions of the hip (SPIROC 1 and

SPIROC 2), and ould not be investigated.

8 Trigger Time Walk and Jitter

As mentioned in Se . 7, SPIROC is forseen to be used in auto-trigger mode

during ILC running onditions. It is ru ial therefore to investigate the size of

the main un ertainties whi h an ae t the trigger timing. Signals with dierent

amplitudes (and same peaking time) ross the dis riminator level at dierent

times, resulting in a time shift (trigger walk) of the generated pro essing trigger,

left panel of Fig. 16. On top of this un ertainty, the rossing of the dis riminator

level is varied in time (trigger jitter) by the noise in the analogue signal, right

panel of Fig. 16.

The trigger time walk and jitter were investigated inje ting a signal from

the pulse generator, and then measuring at the os illos ope the timing of the

oin iden e of the generated trigger in the hip with the main pulse generator

trigger. Dierent threshold values for the analogue signals were set (via the

LabView interfa e) at the 10-bit DAC dis riminator ( ommon to the 36 input

hannels) in the fast shaping line, and dierent harge values were inje ted, thus

allowing for the study of the time walk and jitter dependen e on the trigger

threshold level and on the amplitude of the input signal. The shift of the mean

14

Figure 17: The trigger signal (light blue) is measured in the os illos ope in

oin iden e with the pulse generator trigger (green). The shift of the mean and

the RMS value of the trigger distribution provide the measurement of the trigger

time walk and jitter, respe tively.

and the RMS value of the measured trigger distribution, whi h is shown for a

typi al setting in Fig. 17, provide the measurement of the trigger time walk and

jitter, respe tively. Typi al distributions of the trigger timing above des ribed

are presented in Fig. 18.

The results of the time walk measurements are shown in Fig. 19, for in reas-

ing values of the inje ted harge, from 0.08 up to 1.60 pC (equivalent to one

pixel and 20 ring pixels in an AHCAL SiPM, respe tively), and of the dis rim-

inator threshold level. The time walk values are presented with respe t to the

trigger timing orresponding to the largest inje ted harge. When setting the

threshold value above the pedestal the time walk appears to be up to 7 ns only

for the rst pixel peaks. For a larger number of ring pixels it is within one

nanose ond; this feature is observed also for a threshold at about half a mip

(SiPMs are ongured su h that on average 15 pixels should re due to a mip

energy deposition [3, thus orresponding to 1.2 pC input harge).

The trigger jitter dependen e on the inje ted harge, for dierent values of

the dis riminator threshold, is presented in Fig. 20. The jitter appears to be

up to 1.4 ns, at the smallest threshold values and for small values of inje ted

harge, while it is within 1.0 ns at a threshold of about half a mip.

Con erning the forseen operation of the hip in auto-trigger mode, resolving

single-pixel stru ture in the SiPM spe tra (i.e., in alibration mode) appears

to be not infeasible, due to the reasonably small measured trigger jitter and

time walk At the moment, the SiPM alibration is expe ted to be performed

15

Entries 66013

Mean 50.87

RMS 1.241

Trigger timing [ns]46 48 50 52 54 56 58 60

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4000

4500Entries 66013

Mean 50.87

RMS 1.241

Discriminator Threshold: 0.00pC

Injected Charge: 0.1pC Entries 6184

Mean 44.21

RMS 0.3916

Trigger timing [ns]40 42 44 46 48 50

Yie

ld

0

200

400

600

800

1000

1200Entries 6184

Mean 44.21

RMS 0.3916

Discriminator Threshold: 0.00pC

Injected Charge: 0.7pC

Figure 18: The trigger timing distribution is presented for the dis riminator

threshold value set above the pedestal, and for dierent values of the inje ted

harge in the SPIROC board.

Discriminator threshold at:

pedestal


0.16 pC


0.32 pC


0.64 pC

Injected Charge [pC]

Trigg

er T

ime W

alk [n

s]

0

2

4

6

8

10

12

14

16

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6

Figure 19: The trigger time walk is presented for dierent threshold values of

the 10-bit DAC dis riminator, and for in reasing values of the inje ted harge

in the SPIROC board.

via an LED system providing an external trigger to the ASIC readout. This

issue will be extensively presented in Se . 15. Instead, the small time walk and

jitter values observed at thresholds and input harges above half a mip, should

denitely allow the hip to properly operate in the physi s mode. The inuen e

of largely varying SiPM gain values, light generation and olle tion e ien y

16


pedestal


0.16 pC


0.32 pC


0.64 pC


Trigg

er Ji

tter [

ns]

0

0.2

0.4

0.6

0.8

1

1.2

1.4

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6

Figure 20: The trigger jitter is presented for dierent threshold values of the

10-bit DAC dis riminator, and for in reasing values of the inje ted harge in

the SPIROC board.

has not been studied in this work.

9 SiPM Voltage Adjustment

The hip is forseen to be onne ted to an external power supply and to provide

a ommon high voltage bias to all onne ted 36 SiPMs. Tuning of the applied

voltage, hannel by hannel, is a hieved using an 8-bit DAC HV adjustment

dedi ated to ea h dete tor power line, Fig. 21.

The alibration of the input HV DAC for all hannels is at the moment

performed via dedi ated LabView interfa e routines. The applied voltage ranges

approximately from 0 V to 4.5 V, varying from hannel to hannel, Fig. 22.

The measurements are linearly tted in the range 10-245 DAC units, and

the residual of ea h measurement to the resulted linear fun tion is al ulated.

A large hannel by hannel variation in the residuals size is observed, and two

extreme ases are reported in Fig. 23.

The results show a dierential non-linearity on average up to 70 mV, and

for some hannels up to 200 mV, Fig. 24, resulting in a relative gain hange of

approximatively 1.8% and 5.2% [4, respe tively, and thus providing a potential

systemati un ertainty of similar size to the energy alibration of the dete tor,

in ase the observed deviation annot be systemati ally reprodu ed.

To investigate the reprodu ibility of the voltage tuning applied to the ASIC

hannels, two series of DAC s ans (ve s an per series) were performed for one

hannel in separate periods hara terised by a temperature variation of three

degrees Celsius. Within ea h data set, the maximum deviation between the

17

50

100 nF

Ω10 pF

ASIC

DAC

amplifiershaper

SiPM

cable

100 nF

100k

+HV

Ω

Figure 21: Diagram of the SiPM onne tion to the ASIC board. The same line

is used for both power and signal. While a ommon voltage bias is provided by

an external power supply to all 36 SiPMs onne ted to the ASIC, ea h voltage

is tunable via a separate 8-bit DAC HV adjustment.

measured voltage values was al ulated for ea h DAC value, and is presented in

Fig. 25. As expe ted, for ea h series of measurements the spread in reases with

the DAC value, i.e. with the amount of urrent in the DAC swit h, resulting

in a maximum systemati al deviation up to one millivolt. As a onsequen e,

the observed large dierential non-linearity an be orre ted via a alibration of

hannel by hannel HV adjustment DAC.

Although a negligible deviation is observed among the measurements, when

ombining the two data sets the maximum spread of the measurements in reases

up to 10 mV. This an be possibly interpreted as due to the large variation of

the temperature (up to three Celsius degrees) measured during the systemati al

studies, resulting in a larger applied voltage value observed at a lower temper-

ature. In this ase, the observed hange of voltage adjustment value ould be


Minimum applicable voltage per channel [mV]0 50 100 150 200 250 300

Yie

ld

0

2

4

6

8

10

12

14 Entries 36Mean 90.39RMS 95.68

Figure 22: Distribution of the mini-

mum appli able voltage via the 8-bitDAC HV adjustment. Ea h en-

try represents the minimum volt-

age value measured in one SPIROC

hannel.

18

Voltage Adjustment Set [DAC]0 50 100 150 200 250

Me

as

ure

d V

olt

ag

e [

V]

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

5

Channel Nr. 5

0.00138±Offset: 4.49625

0.00001±Slope: -0.01690

Voltage Adjustment Set [DAC]0 50 100 150 200 250

Me

as

ure

d V

olt

ag

e [

V]

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

5

Channel Nr.16

0.00138±Offset: 4.41819

0.00001±Slope: -0.01639

Voltage Adjustment Set [DAC]0 50 100 150 200 250M

ea

su

red

Vo

lta

ge

Re

sid

ua

ls [

mV

]

-100

-80

-60

-40

-20

0

20

40

60

80

100

Channel Nr. 5

Voltage Adjustment Set [DAC]0 50 100 150 200 250M

ea

su

red

Vo

lta

ge

Re

sid

ua

ls [

mV

]

-100

-80

-60

-40

-20

0

20

40

60

80

100

Channel Nr.16

Figure 23: Upper Panels: Calibration of the high voltage DAC adjustment.

Lower Panels: The residuals of the measurements with respe t to the fun tion

obtained by a linear t.


Max residual per channel [mV]0 20 40 60 80 100 120 140 160 180 200

Yie

ld

0

0.5

1

1.5

2

2.5

3 Entries 36Mean 78.91RMS 39.92

Figure 24: Distribution of the de-

viation from linearity of the high

voltage adjustment. Ea h entry rep-

resents the maximum deviation ob-

served in one hannel.

19

Voltage Adjustment [DAC]0 50 100 150 200 250

Ma

xim

um

Vo

ltag

e D

evi

atio

n [

mV

]

0

2

4

6

8

10

12

CoData taken at T=33CoData taken at T=30

Combined data

Figure 25: The measured maximum deviation of the voltage adjustment applied

to the SPIROC hannels is presented for two separate DAC s ans performed at

dierent temperatures. When ombining the measurements of the two data sets

the spread in reases up to 10 mV.

orre ted via a proper alibration. The alibration might not be needed in ase

of small temperature gradient during data taking, sin e the observed 10 mV sys-

temati al spread is still small ompared to the overvoltage of SiPMs, typi ally

of 2-4 V for the devi es used in urrent AHCAL test beam operations [4. Thus,

this spread would orrespond to a gain hange below 1%.

10 Low Gain - High Gain Coupling

In ea h input hannel of the ASIC the low and high gain paths are ele tri ally

oupled, Fig 26. As a result, the harge sharing between the two paths is

inuen ed by the feedba k apa itan e value set.

In order to estimate the ee ts of the high-low gain oupling, the output

signal in one path was measured for dierent apa itan e values in the other

preamplier line. No signi ant ee t is observed in the output signal of the

high gain line while hanging the ampli ation in the other line. Instead, a

sizable ee t (up to 10%) is visible when measuring the output signal in physi s

mode and hanging the ampli ation in the high gain line. An example of the

observed orrelation is presented in Fig. 27 for dierent values of the harge

inje ted in the ASIC (using a 6.4 dB attenuator at the pulse generator output).

20

1.5 pF

Input

15 pF

Slow Shaper

Slow Shaper

50−100 ns

50−100 ns

0.1 − 1.5 pF

0.1 − 1.5 pF

Fast Shaper

15 ns

PreamplifierHigh Gain

Low GainPreamplifier

Figure 26: Ele tri al diagram of

the high gain and low gain paths

per single hannel in the ASIC

hip.

High Gain Feedback Capacitance [fF]0 100 200 300 400 500 600

Lo

w G

ain

Ou

tpu

t [A

DC

]

40

50

60

70

80 Input charge: 9.6 pC

LG shaping time: 50 ns

LG feedback capacitance: 400 fF










High Gain Feedback Capacitance [fF]0 100 200 300 400 500 600

Lo

w G

ain

Ou

tpu

t [A

DC

]

100

110

120

130

140

150Input charge: 19.1 pC












Figure 27: The output signal (in ADC units) is measured in the low gain path

while hanging the feedba k apa itan e value for the high gain amplier. Here

presented are two measurements obtained using dierent values of input harge

in the ASIC.

11 Cross Talk between Input Channels

The hip will handle 36 in oming signal lines. A ording to previous measure-

ments [2 the estimated ross-talk among the neighbouring hannels is below

0.3% for an inje ted harge of 15 pC. The measurement in [2 was presented for

few inje ted harge values only. This investigation of the ross-talk was done

performing a wider s an of inje ted harge. While in reasing the inje ted harge

in steps of 1 pC from one to 40 pC, orresponding approximately to the range

1−33 mips, the output signal (pedestal subtra ted) was measured in the neigh-

bouring hannels. The ASIC was run in low gain mode (physi s mode) at 50 ns

of shaping time, and 400 fF of feedba k apa itan e.

An example of the performed measurements is presented in Fig. 28. The

output signal in the line where the harge was inje ted is shown in the upper

21

5 10 15 20 25 30 35 40

Sig

na

l o

utp

ut

[mV

]

0

50

100

150

200

Charge injected in channel 5

5 10 15 20 25 30 35 40

Sig

na

l o

utp

ut

[mV

]

-2

-1.5-1

-0.50

0.51

1.52

Injected charge [pC]5 10 15 20 25 30 35 40

Cro

ss

Ta

lk [

%]

-2-1.5

-1-0.5

00.5

11.5

2

channel 4

channel 6

Figure 28: The measurement of the ross-talk is presented for the low gain mode

at 50 ns of shaping time, and 400 fF of feedba k apa itan e.

panel. The reason of the observed non-linearity was found in the tra k and hold

swit h (see Se . 12). In the neighbouring lines the measured signal is typi ally

within ±0.5 mV in the analysed input harge range (middle panel), onrming a

negligible harge leakage between the hannels. A small trend is visible, within

the ±0.5 mV range, moving from small to large inje ted harge. For ea h harge

value the ross-talk (bottom panel) in one hannel was al ulated dividing its

signal (held at its maximum amplitude) to the orresponding signal in the line

where the harge was inje ted. As expe ted by using this method, the ross-

talk inates at small input harge values. At the 15 pC of inje ted harge, the

measurement is lose to what reported in [2.

12 Tra k and Hold Swit h

The hip has to save the amplitude of the pre-amplied and shaped signal

at its peaking time (arrival time of signal maximum). This is a hieved using

the tra k and hold swit h, Fig. 29, whi h holds the signal at the amplitude

orresponding to a provided holding-trigger arrival, to be tuned to hold the

signal at its maximum amplitude.

The peaking time is not expe ted to depend on the amount of inje ted harge

(mainly depending instead on the shaper type [6), and the hoi e of the holding-

trigger should hold for all values of input harge. Surprisingly, it was observed

22

Figure 29: Ele tri al diagram of the

Tra k and Hold swit h.

that the peaking time varies with the harge. The signal amplitude was mea-

sured with the external ADC while performing a s an of the holding-trigger

arrival time, in both low and high gain modes, for 50 ns shaping time, and for

all possible values of the feedba k apa itan e. An example of these measure-

ments is shown in Fig. 30. In these test-ben h measurements the hold signal

is generated by the external voltage sour e. Its arrival time an be arbitrarily

varied to anti ipate or delay it with respe t to peaking amplitude of the inje ted

harge. The measurements show that the peaking time (displayed with a verti-

al line in ea h plot) in reases with in reasing inje ted harge (while remaining

onstant only after rea hing saturation), thus suggesting that either the peaking

time is harge dependent ( ontrary to the expe tations) or that the tra k and

hold swit h somehow interferes with the signal developing in time.

After investigation by the Orsay group, a possible explanation of the ob-

served feature in the small harge region was proposed [7. Due to the small

bias transistor size in the tra k and hold buer (bottom transistor in Fig. 29)

and to the large parasiti apa itan e at its output, small input harge will

make the buer enter the non-linear working region. The investigation with

simulations is on-going by the Orsay group.

13 Dynami Range, Linearity, and Gain of the

ASIC

During normal AHCAL data taking (low gain) the dynami range of the ASIC

should over the region between one mip and ≈ 77 mips (1156 pixels per SiPM

/ 15 pixels ring per mip), onsidering saturation ee ts in the SiPM due to the

limit number of pixels and to the pixel re overy time. Assuming a SiPM gain

of the order of 5 · 105( orresponding to 0.08 pC harge generated per pixel),

the overed dynami mips range orresponds to the region between 1.2 and

92.5 pC. It should be noted that this upper harge limit depends on the spe i

photodete tor gain (MEPhy/Pulsar devi es, onsidered here, have a pixel gain

23

0

100

200

300

400

500

0

200

400

600

800

1000

50 100 50 100

Outp

ut Si

gnal

[mV] Qinj: 10 pC

FC: 100 fF

Qinj: 20 pC Qinj: 30 pC

Outp

ut Si

gnal

[mV] Qinj: 40 pC Qinj: 50 pC

Hold Timing [ns]

Qinj: 60 pC

50 100

0

25

50

75

100

125

150

175

200

225

250

0

100

200

300

400

500

600

50 100 50 100

Outp

ut Si

gnal

[mV] Qinj: 10 pC

FC: 300 fF

Qinj: 20 pC Qinj: 30 pC

Outp

ut Si

gnal

[mV] Qinj: 40 pC Qinj: 50 pC

Hold Timing [ns]

Qinj: 60 pC

50 100

Figure 30: The output signal from the ASIC is measured in low gain mode for

50 ns shaping time and for dierent input harge values, while performing a

s an in the hold arrival time. No attenuator on the input line was used.

24

variation between 0.25 · 106and 1.00 · 106

).

The hip preamplier gain should be hosen su h to provide a linear response

in the whole energy range. On this purpose, a s an was performed over all

feedba k apa itan e values possible in low gain mode, while in reasing the

amount of inje ted harge. For ea h input harge, it was hosen the hold-

trigger timing orresponding to the maximum amplitude for the output signal

measured at the external ADC. This hoi e was motivated by the impossibility of

performing su h a time onsuming multi-parameter s an extra ting the proper

holding-time via the os illos ope, without an automatised pro edure (ea h single

point of the s an was systemati ally measured several times). Systemati ee ts

arising by the tra k and hold swit h, as dis ussed in Se . 12, might ae ts the

results.

The results of this s an, presented in the upper panel of Fig. 31 for 50 ns

shaping time, indi ate that the minimum feedba k apa itan e value needed to

over the required SiPM dynami range (77 mips) is 400 fF. Above this value

the maximum expe ted mip signal an be pro essed before the ASIC runs into

saturation. As a referen e, the values of the inje ted harge are also reported

in terms of equivalent AHCAL mips values.

The sets of data were linearly t in the range 10-30 pC and the residuals to

the linearity were al ulated dividing the deviation of the measured points from

the t results over the t values. A non linearity up to 20% is observed with

in reasing inje ted harge, bottom panel of Fig. 31. The region where the ASIC

saturation appears (anyway not relevant for the forseen operation of the hip)

shows a onsistent drop of the residuals.

Similar measurements were performed operating the hip in high gain mode,

Fig. 32. In this mode, used for alibration, it is preferable to use the largest

(smaller) gain (feedba k apa itan e) to investigate the SiPM single-pixel spe -

tra. The results show that for 100 fF of feedba k apa itan e the saturation

is rea hed for values of input harge above 10 pC, orresponding to a dynami

range up to ≈ 8 mips, enough for performing the alibrations. Note that here

the linear t was performed in the range 1-3 pC.

The observed non linearity is mainly due to the mentioned features of the

tra k and hold swit h, whi h are under investigation and will be possibly ured

in the next generation of the hip. In addition to the observed inje ted harge

dependen e of the peaking time, it was also observed that the peaking amplitude

obtained via the tra k and hold swit h is typi ally larger than what observed

when the signal is not held.

The gain of the hip was al ulated out of the same data a ording to the

formula GASIC =Voutput

Qinput(in

mVpC

units), and is presented in Fig. 33 for dierent

values of the feedba k apa itan e CFC in both low and high gain modes at 50ns shaping time.

In the low (high) gain mode the hip ampli ation fa tor was measured

for 30 pC (3 pC) of inje ted harge, a value not sizably ae ted by the non-

linearity indu ed by the tra k and hold swit h. The expe ted 1/CFC fun tional

dependen e of the gain [5 is observed, quantitatively in agreement with the

25

FC: 100 fF

FC: 300 fF

FC: 500 fF

FC: 700 fF

FC: 1000 fF

FC: 1500 fF

Shaping time: 50 ns Low Gain


Outp

ut A

SIC

[mV]

Equivalent mips

0

200

400

600

800

1000

0 50 100 150 200 250 300

0 25 50 75 100 125 150 175 200 225 250

FC: 100 fF

FC: 300 fF

FC: 500 fF

FC: 700 fF

FC: 1000 fF

FC: 1500 fF

Shaping time: 50 ns

Low Gain


Resid

uals

to li

near

ity [%

]

Equivalent mips

-60

-40

-20

0

20

40

0 25 50 75 100 125 150 175 200 225 250

0 20 40 60 80 100 120 140 160 180 200

-10

-5

0

5

10

0 20 40

Figure 31: The output signal from the ASIC is measured in low gain mode for

50 ns shaping time and for dierent input harge values. Upper panel: Results

obtained using dierent feedba k apa itan e values are ompared. Bottom

Panel: Residuals to linearity al ulated as des ribed in the text.

measurements presented in [2 and [8.

26

FC: 100 fF

FC: 300 fF

FC: 500 fF

FC: 700 fF

FC: 1000 fF

FC: 1500 fF

Shaping time: 50 ns High Gain


Outp

ut A

SIC

[mV]

Equivalent mips

0

200

400

600

800

1000

1200

1400

0 10 20 30 40

0 5 10 15 20 25 30 35

FC: 100 fF

FC: 300 fF

FC: 500 fF

FC: 700 fF

FC: 1000 fF

FC: 1500 fF

Shaping time: 50 ns

High Gain


Resid

uals

to li

near

ity [%

]

Equivalent mips

-60

-40

-20

0

20

40

0 5 10 15 20 25 30 35 40 45

0 5 10 15 20 25 30 35

-5

0

5

0 5

Figure 32: The output signal from the ASIC is measured in high gain mode for

50 ns shaping time and for dierent input harge values. Upper panel: Results

obtained using dierent feedba k apa itan e values are ompared. Bottom

Panel: Residuals to linearity al ulated as des ribed in the text. A 20 dB

attenuator at the input line was used during these measurements.

27

Shaping time: 50 ns

Low Gain

Qinj: 30 pC

Feedback Capacitance [fF]

Gain

[mV/

pC]

0

2

4

6

8

10

12

14

16

18

20

0 200 400 600 800 1000 1200 1400 1600

Shaping time: 50 ns

High Gain

Qinj: 3 pC

Feedback Capacitance [fF]

Gain

[mV/

pC]

0

20

40

60

80

100

120

0 200 400 600 800 1000 1200 1400 1600

Figure 33: The gain of the ASIC is measured in both low and high gain modes

for 50 ns shaping time and for 30 pC and 3 pC of inje ted harge, respe tively.

14 Amplitude Dependen e on Shaping Time

The ee t of the shaping time value on the measured signal peaking amplitude

was investigated. The amplitude was measured operating the ASIC in low gain

mode for dierent values of the shaping time and for the feedba k apa itan e

value of 400 fF, Fig. 34. Dierently from what presented in Fig. 31, here a 20 dB

28

Shaping Time: 50 ns

Shaping Time: 75 ns

Shaping Time: 100 ns


Feedback Capacitance: 400 fF Low Gain


Outp

ut A

SIC

[mV]

Equivalent mips

0

50

100

150

200

250

300

0 5 10 15 20 25 30 35 40

0 5 10 15 20 25 30

Shaping Time: 50 ns

Shaping Time: 75 ns



Feedback Capacitance: 400 fF Low Gain


Resid

uals

to li

near

ity [%

]

Equivalent mips

-100

-80

-60

-40

-20

0

20

40

60

80

100

0 5 10 15 20 25 30 35 40

0 5 10 15 20 25 30

Figure 34: Upper panel: The output signal from the ASIC is measured in low

gain mode for 400 fF feedba k apa itan e, and for dierent values of inje ted

harge and of shaping time. Bottom Panel: Residuals to linearity al ulated as

des ribed in the text. A 20 dB attenuator (10−1X) at the input line was used

during these measurements.

29

attenuator was used, to present results at small inje ted harge in ner binning.

Also, results are presented for harge values down to 1 pC.

The signal peaking amplitude appears to in rease with de reasing shaping

time, in agreement with simulations. The sets of data were linearly t in the

range 1-4 pC and the residuals to the linearity were al ulated dividing the

deviation of the measured points from the t results over the t values. A non

linearity up to 40% is observed for in reasing inje ted harge, bottom panel

of Fig. 34. In this region of inje ted harge values the non-linearity response

(due to the tra k and hold swit h) appears to be weakly dependent on the

hosen shaping time. Note that a dire t omparison with the results presented

in the bottom panel of Fig. 31 annot be done, being dierent both the region

onsidered in the linear t and the smallest values of inje ted harge onsidered

in these measurements.

15 SiPM Single-Pixel Spe tra

The possibility to operate the ASIC in auto-trigger mode during alibrations

was shown to be feasible due to the low trigger jitter time walk, smaller than 1and 7 ns, respe tively (see Se . 8). That possibility is onrmed by the followingmeasurement of the single-pixel spe trum.

A SiPM, ashed by an LED, was onne ted to the board, and the pro essed

output signal was investigated. The devi e was operated at overvoltage larger

(+1.7 V) than the nominal value, to in rease the ross-talk between the pixels

(whi h is, on the other side, not desirable for physi s mode operations). The

SiPM signal was measured using the auto-trigger mode des ribed in Se .7. After

properly setting a dis riminator threshold value, the generated trigger was used

to trigger an external pulse generator (HP 8082A). One signal from the pulser

was then used to open the gate of the external ADC module, and a se ond signal

was input to the SPIROC board to hold the analogue signal from the SiPM at

its peaking amplitude.

When the dis riminator threshold is set above the pedestal the ontribution

of the thermal noise dominates the measured spe trum, Fig. 35, due to its large

rate (typi ally around MHz).

In order to observe the ontribution of LED light indu ed events in the

spe trum, the dis riminator threshold was set to 480 DAC units, orresponding

to a value approximately above 3 pixels for a measured gain of 13 mV per

pixel (operating the SiPM at 64.7 V), Fig. 36. Also, the rate of the LED

ashes was in reased to 30 kHz from the initial 1 kHz. Although the thermal

noise ontribution appears to be still sizable in this experimental onguration

(dominating the spe trum rst peaks), the LED signal appears in the spe trum

at large amplitude values, and is also presented in the zoomed panel of the

pi ture. The results show the single-pixel stru ture, and suggest that a t of

the spe trum (either the thermal noise or the signal ontribution) might be

possible, although its quality annot be quantied at this stage of the analysis.

The above results were obtained for a quite large gain of the SiPM. To see

30

/ ndf 2χ 359.4 / 50Prob 0p0 41.2± 6699 p1 0.0± 12.6 p2 0.013± 2.676 p3 29.2± 3445 p4 0.02± 25.13 p5 0.027± 3.153 p6 18.2± 1497 p7 0.04± 38.03 p8 0.057± 3.545 p9 11.2± 668.5 p10 0.09± 51.16 p11 0.116± 3.733 p12 8.2± 312 p13 0.16± 64.54 p14 0.229± 4.529

Amplitude [mV]0 10 20 30 40 50 60 70 80 90 100

Yiel

d

0

1000

2000

3000

4000

5000

6000

7000 / ndf 2χ 359.4 / 50Prob 0p0 41.2± 6699 p1 0.0± 12.6 p2 0.013± 2.676 p3 29.2± 3445 p4 0.02± 25.13 p5 0.027± 3.153 p6 18.2± 1497 p7 0.04± 38.03 p8 0.057± 3.545 p9 11.2± 668.5 p10 0.09± 51.16 p11 0.116± 3.733 p12 8.2± 312 p13 0.16± 64.54 p14 0.229± 4.529

p.e.0 1 2 3 4 5

SiPM 711

: 12.8 mVp.e.

<gain>

DAC: 565

Voltage Bias: 64.7 V

Figure 35: Single-pixel spe trum for the thermal noise obtained by operating

the SiPM in high gain (13 mV per pixel) and for the dis riminator threshold

level above the pedestal. Superimposed is the gaussian t to the peak stru ture

of the spe trum.

the ee ts of a lower pixel gain value, the voltage bias applied to the devi e was

de reased to 63.0 V resulting in a gain around 8 mV per pixel, whi h orresponds

Amplitude [mV]0 50 100 150 200 250 300 350 400

Yiel

d

0

20

40

60

80

100

120

140

160

180310×

Amplitude [mV]160 180 200 220 240 260 280 300

Yiel

d

13000

13500

14000

14500

15000

15500

16000

16500

17000

SiPM 711 : 13.0 mVp.e.

<gain>

DAC: 480 Voltage Bias: 64.7 V

Figure 36: Single-pixel spe trum obtained by ashing the SiPM with LED light.

The devi e was operated in high pixel gain (13 mV per pixel) setting the SPIROC

dis riminator threshold level above the third pixel peak, and running the ASIC

in auto-trigger mode. The ontribution from the thermal noise and the LED

events dominates the rst peaks and the high tail of the spe trum, respe tively.

The peak stru ture of part of the spe trum for LED driven events is also pre-

sented in the zoomed panel for better visibility.

31

Amplitude [mV]0 20 40 60 80 100 120 140 160 180 200

Yiel

d

0

20

40

60

80

100

120

140

160

180310×

SiPM 711

: 8.0 mVp.e.

<gain>

DAC: 480



The devi e was operated in low pixel gain (8 mV per pixel) setting the SPIROC

dis riminator threshold level above the fth pixel peak, and running the ASIC

in auto-trigger mode. Due to the lower devi e gain and to the high dis rimi-

nator threshold value the ontribution from the thermal noise is here strongly

suppressed, and the spe trum is mainly populated by LED driven events.

to approximately half a million ele trons. The dis riminator threshold value was

kept un hanged, orresponding at about ve pixels at this low pixel gain. The

resulting spe trum is presented in Fig. 37. Due to the lower devi e gain and to

the high dis riminator threshold value the ontribution from the thermal noise is

here strongly suppressed, and the spe trum is mainly populated by LED driven

events.

To see the quality of the noise spe trum for this low SiPM gain, the threshold

was set above the pedestal, Fig. 38. At this low pixel gain value, the single-pixel

stru ture of the thermal noise spe trum appears to be deteriorated, ompli ating

the possibility to perform a t of the pixel stru ture to alibrate the devi e. This

ompli ation might be over ome by operating the SiPM with a larger gain, as

shown in Fig. 35 .

As a omparison, the measurement was repeated using an external trigger to

hold the peaking amplitude and to open the gate of the ADC module, operating

the SiPM at low pixel gain and setting the dis riminator threshold value above

the pedestal. The LED intensity was de reased to have a lower number of pixels

ring, similarly to what is usually done alibrating a SiPM with an LED system.

The single-pixel spe trum, now without any ontribution from the thermal noise,

is presented in Fig. 39. The peaks appear to be well separated, allowing the

alibration of the devi e using an external light sour e system. Potentially, the

alibration of the photodete tor might be also performed running the SPIROC

in auto-trigger mode by analysing the thermal noise. In this ase, during the

alibration the SiPM should be operated at larger pixel gains, as shown above.

32

Amplitude [mV]0 20 40 60 80 100 120 140 160 180

Yiel

d

0

100

200

300

400

500

600

310×

Amplitude [mV]50 60 70 80 90 100 110 120

Yiel

d

25000

30000

35000

40000

45000

50000

55000

SiPM 711 : 8.0 mVp.e.

<gain>

DAC: 560 Voltage Bias: 63.0 V


The devi e was operated in low pixel gain (8 mV per pixel) setting the SPIROC

dis riminator threshold level above the pedestal, and running the ASIC in auto-

trigger mode. The ontribution from the thermal noise and the LED events

dominates the rst peaks and the high tail of the spe trum, respe tively. The

peak stru ture of part of the spe trum for LED driven events is also presented

in the zoomed panel for better visibility.

Amplitude [mV]0 20 40 60 80 100 120 140

Yiel

d

0

10000

20000

30000

40000

50000

60000

SiPM 711

: 8.0 mVp.e.

<gain>

DAC: 575


External Trigger

Figure 39: Typi al SiPM single-pixel spe tra obtained by ashing the SiPM

with LED light. The devi e was operated in low pixel gain (8 mV per pixel)

setting the SPIROC dis riminator threshold level above the pedestal. Here, the

signal is held at its peaking amplitude by an external trigger given by the main

pulse generator.

33

16 Towards Real Data Taking Conditions

When the measurements presented in this note have been performed, the soft-

ware to operate the hip in auto-trigger mode (see Se . 7) was not fully im-

plemented. This limitation ould be somehow bypassed using the following

pro edure, thus testing the apability and the e ien y of the hip to perform

measurements in both physi s and auto-trigger mode at dierent trigger thresh-

old values, Fig. 40.

These measurements were performed using the signal from a SiPM (SiPM

number 758), thus simulating, as mu h as possible, real data taking onditions.

Spe tra suitable for tting the single-pixel stru ture of the signal were obtained

operating the high voltage supply at 64.6 V, orresponding to 59.4 V voltage

bias measured at the dynodes of SiPM by setting the input HV DAC tuning

to zero units (see Se . 9). Note that the nominal operation voltage for this

SiPM is 59.3 V, as de lared in the SiPM database. The main pulse generator

triggered the generation of a negative voltage pulse (via a Hewlett Pa kard

8130A pulse generator providing width, leading and trailing edges tunable down

to the nanose ond level) to an LED, opti ally oupled to a SiPM whose signal

was then dire tly input to the ASIC board, using the same high voltage line,

Fig. 21. The intensity of the LED, and in turns of the SiPM signal, ould be

then regulated by the hained pulser.

During test-ben h measurements the signal to open the ADC module gate

is typi ally provided by the pulse generator, for every generated voltage pulse.

A essing the trigger allows instead to generate the open-gate signal only in ase

ADC module

CAEN V785N

bufferamplifier1x or 9x

VME CAEN 8002

hold

ASICSiPM

+HV

pulse generator

STS DG 535

pulse generatortrigger

HP 8130A

generatorgate

STS DG 535

pulse generator

Figure 40: Test ben h setup used at DESY for the investigation of the e ien y

of the SPIROC 1B hip to perform measurements in physi s and auto-trigger

mode at dierent trigger threshold values.

34

DAC value Suppressed peak number

530 3510 4490 5470 6450 7430 8410 9390 10

Table 1: DAC values applied at the

signal dis riminator to suppress spe-

i peaks in the SiPM spe trum.

The obtained DAC values refer to

the hip operated in high gain mode

at 25 ns shaping time and 100 fF

feedba k apa itan e. One DAC

units orresponds to ≈ 1.9 mV in

the fast shaping line.

a pro essed signal (either from the thermal noise or from the LED) overshoots a

hosen threshold value in the dis riminator. The generated trigger was therefore

used as an external trigger to an additional pulse generator, whi h in turns

generated the signal to open the ADC module gate at a suitable time. The hold

signal was provided by the main pulser used to swit h the LED on.

As a rst step, the hip was operated in high gain mode in parallel with

low intensity LED light, while applying dierent threshold DAC values via the

LabView interfa e (the larger is the DAC value set, the smaller is the applied

threshold level value). Using the trigger only to open the ADC gate, but holding

the signal peaking amplitude via the external primary pulse generator allowed to

easily t the single-pixel stru ture of the spe trum orresponding to LED events,

for the purpose of this measurement, Fig. 41- 42. In ase a signal indu ed by

thermal noise overshoots the dis riminator threshold level then the ADC gate

is still opened by the generated trigger but the pro essed signal is not any more

syn hronised with the hold signal generated by the main pulser. This results in

deteriorating the single-pixel stru ture of the thermal noise ontribution, and

populating the spe trum towards the pedestal region (the re orded signal ampli-

tude is lower than the real peaking amplitude). This ontribution from thermal

noise to the spe trum is in reasingly suppressed with in reasing the threshold

value, as learly visible in Fig. 41. Although the number of suppressed peaks in

the spe trum in reases by in reasing the threshold level, the measurements show

that a remaining small ontribution from the peaks expe ted to be suppressed

is still present. This feature, possibly due to the experimental setup, has not

been furtherly investigated at this stage of the analysis, being not relevant for

the measurement presented here.

From the above measurements the threshold values to ut spe i spe trum

peaks an be determined resulting in approximative 20 DAC units per peak,

Tab. 1. This orresponds to a step of ≈ 37 mV in the fast shaping line (see

Fig. 14).

As a ross he k, a similar spe trum was taken using the pulse generator

to open the ADC gate, obtaining the same single-pixel peak lo ations, Fig. 43.

With the same setup, a mip signal was tentatively obtained tuning the LED

amplitude su h that the SiPM spe trum shows a maximum around the 15 pixel

peak amplitude, Fig. 44. Keeping the same LED amplitude, the mip-like signal

35

/ ndf 2χ 396 / 402Prob 0.5756p0 3.4± 306.1 p1 0.12± 20.55 p2 0.323± 4.078 p3 22.4± 254.2 p4 0.18± 29.15 p5 0.187± -2.443 p6 19.2± 291.3 p7 0.25± 36.18 p8 0.439± -3.118 p9 15.5± 253.7 p10 0.32± 44.34 p11 0.598± 3.423 p12 41.4± 113.3 p13 0.45± 51.68 p14 0.456± 2.558 p15 3.4± 190.2 p16 0.74± 59.38 p17 1.078± 6.613

Amplitude [mV]20 30 40 50 60 70 80 90 100 110

Yie

ld

0

100

200

300

400

500

600 / ndf 2χ 396 / 402

Prob 0.5756p0 3.4± 306.1 p1 0.12± 20.55 p2 0.323± 4.078 p3 22.4± 254.2 p4 0.18± 29.15 p5 0.187± -2.443 p6 19.2± 291.3 p7 0.25± 36.18 p8 0.439± -3.118 p9 15.5± 253.7 p10 0.32± 44.34 p11 0.598± 3.423 p12 41.4± 113.3 p13 0.45± 51.68 p14 0.456± 2.558 p15 3.4± 190.2 p16 0.74± 59.38 p17 1.078± 6.613

p.e.2 3 4 5 6 7 8

SiPM 758

: 7.4 mVp.e.

<gain>

DAC: 570


/ ndf 2χ 424.5 / 402Prob 0.2112p0 3.6± 346.1 p1 0.09± 21.52 p2 0.198± 3.875 p3 16.0± 368.3 p4 0.11± 29.76 p5 0.118± -2.397 p6 20.7± 397.4 p7 0.16± 36.63 p8 0.243± -2.866 p9 34.0± 356.6 p10 0.28± 44.56 p11 0.385± 3.553 p12 40.7± 135.6 p13 0.28± 52.37 p14 0.318± -2.424 p15 3.9± 262 p16 0.82± 59.53 p17 1.420± 7.497

Amplitude [mV]20 30 40 50 60 70 80 90 100 110

Yie

ld

0

100

200

300

400

500

600 / ndf 2χ 424.5 / 402

Prob 0.2112p0 3.6± 346.1 p1 0.09± 21.52 p2 0.198± 3.875 p3 16.0± 368.3 p4 0.11± 29.76 p5 0.118± -2.397 p6 20.7± 397.4 p7 0.16± 36.63 p8 0.243± -2.866 p9 34.0± 356.6 p10 0.28± 44.56 p11 0.385± 3.553 p12 40.7± 135.6 p13 0.28± 52.37 p14 0.318± -2.424 p15 3.9± 262 p16 0.82± 59.53 p17 1.420± 7.497

p.e.2 3 4 5 6 7 8

SiPM 758

: 7.4 mVp.e.

<gain>

DAC: 560


/ ndf 2χ 418.6 / 402Prob 0.2736p0 3.4± 326.9 p1 0.09± 21.17 p2 0.188± 3.871 p3 8.2± 453.5 p4 0.06± 29.72 p5 0.08± -2.43 p6 8.2± 518.9 p7 0.08± 36.67 p8 0.080± -2.707 p9 35.4± 449.8 p10 0.11± 44.31 p11 0.127± 3.309 p12 29.5± 177 p13 0.14± 51.89 p14 0.170± 2.498 p15 3.0± 334.1 p16 0.59± 59.11 p17 1.04± -8.06

Amplitude [mV]20 30 40 50 60 70 80 90 100 110

Yie

ld

0

100

200

300

400

500

600 / ndf 2χ 418.6 / 402

Prob 0.2736p0 3.4± 326.9 p1 0.09± 21.17 p2 0.188± 3.871 p3 8.2± 453.5 p4 0.06± 29.72 p5 0.08± -2.43 p6 8.2± 518.9 p7 0.08± 36.67 p8 0.080± -2.707 p9 35.4± 449.8 p10 0.11± 44.31 p11 0.127± 3.309 p12 29.5± 177 p13 0.14± 51.89 p14 0.170± 2.498 p15 3.0± 334.1 p16 0.59± 59.11 p17 1.04± -8.06

p.e.2 3 4 5 6 7 8

SiPM 758

: 7.4 mVp.e.

<gain>

DAC: 550


/ ndf 2χ 394.6 / 402Prob 0.5942p0 3.2± 275.7 p1 0.11± 20.83 p2 0.295± 4.261 p3 13.5± 534.8 p4 0.1± 30 p5 0.088± 2.427 p6 20.0± 782.8 p7 0.11± 37.09 p8 0.138± 2.708 p9 16.7± 788.3 p10 0.10± 44.56 p11 0.237± 3.064 p12 69.9± 434.8 p13 0.24± 51.58 p14 0.245± -2.725 p15 5.9± 567.3 p16 0.38± 59.73 p17 0.573± 6.151

Amplitude [mV]20 30 40 50 60 70 80 90 100 110

Yie

ld

0

200

400

600

800

1000 / ndf 2χ 394.6 / 402

Prob 0.5942p0 3.2± 275.7 p1 0.11± 20.83 p2 0.295± 4.261 p3 13.5± 534.8 p4 0.1± 30 p5 0.088± 2.427 p6 20.0± 782.8 p7 0.11± 37.09 p8 0.138± 2.708 p9 16.7± 788.3 p10 0.10± 44.56 p11 0.237± 3.064 p12 69.9± 434.8 p13 0.24± 51.58 p14 0.245± -2.725 p15 5.9± 567.3 p16 0.38± 59.73 p17 0.573± 6.151

p.e.2 3 4 5 6 7 8

SiPM 758

: 7.4 mVp.e.

<gain>

DAC: 540


/ ndf 2χ 425.4 / 412Prob 0.3143p0 1.61± 88.64 p1 0.20± 20.26 p2 0.428± 5.235 p3 4.5± 157.7 p4 0.09± 30.42 p5 0.098± 2.304 p6 5.2± 301.5 p7 0.09± 37.61 p8 0.116± 2.658 p9 11.1± 332.1 p10 0.13± 44.91 p11 0.181± 2.836 p12 5.0± 236.8 p13 0.45± 61.06 p14 0.490± 5.373 p15 28.9± 236 p16 0.17± 52.17 p17 0.324± 3.225

Amplitude [mV]20 30 40 50 60 70 80 90 100 110

Yie

ld

0

100

200

300

400

500

600 / ndf 2χ 425.4 / 412

Prob 0.3143p0 1.61± 88.64 p1 0.20± 20.26 p2 0.428± 5.235 p3 4.5± 157.7 p4 0.09± 30.42 p5 0.098± 2.304 p6 5.2± 301.5 p7 0.09± 37.61 p8 0.116± 2.658 p9 11.1± 332.1 p10 0.13± 44.91 p11 0.181± 2.836 p12 5.0± 236.8 p13 0.45± 61.06 p14 0.490± 5.373 p15 28.9± 236 p16 0.17± 52.17 p17 0.324± 3.225

p.e.2 3 4 5 6 7 8

SiPM 758

: 7.5 mVp.e.

<gain>

DAC: 530


/ ndf 2χ 420.8 / 392Prob 0.1519p0 1.69± 84.12 p1 0.17± 20.49 p2 0.419± 3.551 p3 3.0± 101.6 p4 0.21± 30.46 p5 0.337± 3.065 p6 8.8± 305.6 p7 0.13± 38.28 p8 0.156± 2.613 p9 14.6± 434.4 p10 0.15± 45.59 p11 0.219± 2.787 p12 48.2± 371.5 p13 0.19± 52.58 p14 0.315± -2.841 p15 5.3± 373 p16 0.32± 60.91 p17 0.663± 4.378

Amplitude [mV]20 30 40 50 60 70 80 90 100 110

Yie

ld

0

100

200

300

400

500

600 / ndf 2χ 420.8 / 392

Prob 0.1519p0 1.69± 84.12 p1 0.17± 20.49 p2 0.419± 3.551 p3 3.0± 101.6 p4 0.21± 30.46 p5 0.337± 3.065 p6 8.8± 305.6 p7 0.13± 38.28 p8 0.156± 2.613 p9 14.6± 434.4 p10 0.15± 45.59 p11 0.219± 2.787 p12 48.2± 371.5 p13 0.19± 52.58 p14 0.315± -2.841 p15 5.3± 373 p16 0.32± 60.91 p17 0.663± 4.378

p.e.2 3 4 5 6 7 8

SiPM 758

: 7.5 mVp.e.

<gain>

DAC: 520


Figure 41: The spe trum from SiPM nr.758 is measured in high gain mode ap-

plying dierent threshold DAC values at the signal dis riminator lo ated along

the fast shaping line. The hip is operated in high gain mode at 25 ns shaping

time and 100 fF feedba k apa itan e.

was then measured using the low gain mode of the hip, Fig. 45, for a shaping

time of 50 ns.

36

/ ndf 2χ 386.4 / 392Prob 0.5706p0 1.58± 79.15 p1 0.28± 20.25 p2 0.630± 4.267 p3 4.56± 73.28 p4 0.25± 30.24 p5 0.338± 2.917 p6 5.6± 302.6 p7 0.15± 38.95 p8 0.179± 2.907 p9 18.7± 499.5 p10 0.11± 45.83 p11 0.142± 2.433 p12 66.9± 459.4 p13 0.14± 52.38 p14 0.275± -2.814 p15 5.1± 503.5 p16 0.3± 60.9 p17 0.782± 4.994

Amplitude [mV]20 30 40 50 60 70 80 90 100 110

Yie

ld

0

100

200

300

400

500

600

/ ndf 2χ 386.4 / 392Prob 0.5706p0 1.58± 79.15 p1 0.28± 20.25 p2 0.630± 4.267 p3 4.56± 73.28 p4 0.25± 30.24 p5 0.338± 2.917 p6 5.6± 302.6 p7 0.15± 38.95 p8 0.179± 2.907 p9 18.7± 499.5 p10 0.11± 45.83 p11 0.142± 2.433 p12 66.9± 459.4 p13 0.14± 52.38 p14 0.275± -2.814 p15 5.1± 503.5 p16 0.3± 60.9 p17 0.782± 4.994

p.e.2 3 4 5 6 7 8

SiPM 758

: 7.5 mVp.e.

<gain>

DAC: 510


/ ndf 2χ 426.8 / 396Prob 0.1379p0 1.67± 75.36 p1 0.16± 20.41 p2 0.313± 3.047 p3 1.58± 67.76 p4 0.19± 29.54 p5 0.350± 3.204 p6 4.2± 215.7 p7 0.18± 39.44 p8 0.190± 3.015 p9 21.0± 494.3 p10 0.10± 46.15 p11 0.108± 2.292 p12 36.0± 627.1 p13 0.15± 52.94 p14 0.216± 3.005 p15 7.8± 659.5 p16 0.19± 61.42 p17 0.369± 4.012

Amplitude [mV]20 30 40 50 60 70 80 90 100 110

Yie

ld

0

100

200

300

400

500

600

700

/ ndf 2χ 426.8 / 396Prob 0.1379p0 1.67± 75.36 p1 0.16± 20.41 p2 0.313± 3.047 p3 1.58± 67.76 p4 0.19± 29.54 p5 0.350± 3.204 p6 4.2± 215.7 p7 0.18± 39.44 p8 0.190± 3.015 p9 21.0± 494.3 p10 0.10± 46.15 p11 0.108± 2.292 p12 36.0± 627.1 p13 0.15± 52.94 p14 0.216± 3.005 p15 7.8± 659.5 p16 0.19± 61.42 p17 0.369± 4.012

p.e.2 3 4 5 6 7 8

SiPM 758

: 7.6 mVp.e.

<gain>

DAC: 500


/ ndf 2χ 266.5 / 249Prob 0.2135p0 7.5± 460.1 p1 0.14± 47.08 p2 0.105± -3.043 p3 40.1± 719.8 p4 0.12± 53.75 p5 0.121± -2.411 p6 109.8± 717.4 p7 0.2± 60.2 p8 0.313± 3.073 p9 12.9± 773.7 p10 0.38± 68.83 p11 0.796± 4.916

Amplitude [mV]30 40 50 60 70 80 90 100 110

Yie

ld

0

100

200

300

400

500

600

700

800

900

/ ndf 2χ 266.5 / 249Prob 0.2135p0 7.5± 460.1 p1 0.14± 47.08 p2 0.105± -3.043 p3 40.1± 719.8 p4 0.12± 53.75 p5 0.121± -2.411 p6 109.8± 717.4 p7 0.2± 60.2 p8 0.313± 3.073 p9 12.9± 773.7 p10 0.38± 68.83 p11 0.796± 4.916

p.e.4 5 6 7 8

SiPM 758

: 7.7 mVp.e.

<gain>

DAC: 490


/ ndf 2χ 224.2 / 249Prob 0.8686p0 9.4± 320.3 p1 0.21± 47.43 p2 0.148± 2.806 p3 17.5± 797 p4 0.09± 54.28 p5 0.13± -2.57 p6 82.9± 711.2 p7 0.12± 60.57 p8 0.180± -2.559 p9 6.3± 1078 p10 0.19± 68.74 p11 0.43± -5.57

Amplitude [mV]40 50 60 70 80 90 100 110

Yie

ld

0

200

400

600

800

1000

1200

/ ndf 2χ 224.2 / 249Prob 0.8686p0 9.4± 320.3 p1 0.21± 47.43 p2 0.148± 2.806 p3 17.5± 797 p4 0.09± 54.28 p5 0.13± -2.57 p6 82.9± 711.2 p7 0.12± 60.57 p8 0.180± -2.559 p9 6.3± 1078 p10 0.19± 68.74 p11 0.43± -5.57

p.e.5 6 7 8 9

SiPM 758

: 7.7 mVp.e.

<gain>

DAC: 480


/ ndf 2χ 222.8 / 234Prob 0.6896p0 24.1± 244.9 p1 0.35± 62.06 p2 0.291± 2.571 p3 56.1± 410.9 p4 0.18± 69.11 p5 0.439± 3.057 p6 7.7± 461.6 p7 0.89± 83.44 p8 1.838± 6.836 p9 124.8± 249.1 p10 0.43± 75.77 p11 0.528± 2.649

Amplitude [mV]60 70 80 90 100 110

Yie

ld

0

100

200

300

400

500

600

/ ndf 2χ 222.8 / 234Prob 0.6896p0 24.1± 244.9 p1 0.35± 62.06 p2 0.291± 2.571 p3 56.1± 410.9 p4 0.18± 69.11 p5 0.439± 3.057 p6 7.7± 461.6 p7 0.89± 83.44 p8 1.838± 6.836 p9 124.8± 249.1 p10 0.43± 75.77 p11 0.528± 2.649

p.e.7.5 8 8.5 9 9.5 10 10.5 11 11.5

SiPM 758

: 7.6 mVp.e.

<gain>

DAC: 450


/ ndf 2χ 219.9 / 181Prob 0.02573p0 12.2± 203 p1 0.23± 70.43 p2 0.214± 3.142 p3 37.6± 189.3 p4 0.17± 76.64 p5 0.218± -2.232 p6 4.0± 438.7 p7 0.17± 84.53 p8 0.6± 5.7

Amplitude [mV]65 70 75 80 85 90 95 100 105 110

Yie

ld

0

100

200

300

400

500

600

/ ndf 2χ 219.9 / 181Prob 0.02573p0 12.2± 203 p1 0.23± 70.43 p2 0.214± 3.142 p3 37.6± 189.3 p4 0.17± 76.64 p5 0.218± -2.232 p6 4.0± 438.7 p7 0.17± 84.53 p8 0.6± 5.7

p.e.8.5 9 9.5 10 10.5 11

SiPM 758

: 7.7 mVp.e.

<gain>

DAC: 430


Figure 42: The spe trum from SiPM nr.758 is measured in high gain mode ap-

plying dierent threshold DAC values at the signal dis riminator lo ated along

the fast shaping line. The hip is operated in high gain mode at 25 ns shaping

time and 100 fF feedba k apa itan e.

Using again the generated trigger to open the ADC gate, and applying dif-

ferent threshold DAC values, the trigger e ien y with respe t to the signal

37

/ ndf 2χ 532.3 / 516

Prob 0.3006

Amplitude [mV]0 20 40 60 80 100

Yie

ld

0

100

200

300

400

500

600 / ndf 2χ 532.3 / 516

Prob 0.3006

p.e.0 2 4 6 8 10

SiPM 758

: 7.7 mVp.e.

<gain>

DAC: 400


Peak 0: -0.89 +- 0.070Peak 1: 6.46 +- 0.051Peak 2: 14.19 +- 0.054Peak 3: 21.80 +- 0.058Peak 4: 29.36 +- 0.082Peak 5: 37.15 +- 0.088Peak 6: 44.36 +- 0.154Peak 7: 53.01 +- 0.232








Figure 43: The SiPM single pixel

spe trum obtained operating the

hip in high gain mode at 25 ns

shaping time and 100 fF feedba k

apa itan e, and using the main ex-

ternal pulse generator to open the

ADC gate.

Amplitude [mV]20 40 60 80 100 120 140 160 180 200 220

Yie

ld

0

50

100

150

200

250

300

350

400

450

500

p.e.5 10 15 20 25

SiPM 758


Figure 44: A mip-like signal mea-

sured operating the hip in high gain

mode at 25 ns shaping time and

100 fF feedba k apa itan e.

dis rimination level was investigated for two values of the feedba k apa itan e,

Fig. 46. In the plots, the threshold DAC values are presented in terms of num-

ber of photo-ele tron peaks whi h are ut by the sele ted threshold, a ording

to Tab. 1. By in reasing the DAC value (de reasing the trigger threshold) the

number of triggers generated by the noise in reases, resulting in a larger on-

tribution of pedestal events to the overall a umulated events in the spe tra.

Already at half a mip threshold the fra tional ontribution of SiPM signal events

is almost 100%, for both the investigated ASIC ongurations.

The preliminary results presented here verify the possibility to operate the

ASIC in auto-trigger mode (after the mentioned improvement of the tra k and

hold swit h) pro essing the physi s events at half a mip ut on the trigger

threshold, as forseen in the ILC appli ations.

38

Amplitude [ADC]

1100 1120 1140 1160 1180 1200

Yiel

d

0

20

40

60

80

100310×

SiPM 758


mip-like signal

Amplitude [ADC]

1100 1120 1140 1160 1180 1200

Yiel

d

0

50

100

150

200

250

300

350

400310×

pedestal

Figure 45: A mip-like signal (left panel) and the pedestal (right panel) are

measured operating the hip in low gain mode at 50 ns shaping time and 200 fF

feedba k apa itan e.

Amplitude [ADC]1130 1140 1150 1160 1170 1180 1190 1200

Yie

ld

0

50

100

150

200

250

300

350

400310×

SiPM 758

50 ns shaping time

200 fF feedb. capacitance

Fraction of mip events2.0 p.e.: 0.159

3.5 p.e.: 0.4445.0 p.e.: 0.832

7.5 p.e.: 0.98611.0 p.e.: 0.999

12.0 p.e.: 1.000

2.0 p.e.: 0.159

3.5 p.e.: 0.4445.0 p.e.: 0.832

7.5 p.e.: 0.98611.0 p.e.: 0.999

12.0 p.e.: 1.000

2.0 p.e.: 0.159

3.5 p.e.: 0.4445.0 p.e.: 0.832

7.5 p.e.: 0.98611.0 p.e.: 0.999

12.0 p.e.: 1.000

2.0 p.e.: 0.159

3.5 p.e.: 0.4445.0 p.e.: 0.832

7.5 p.e.: 0.98611.0 p.e.: 0.999

12.0 p.e.: 1.000

2.0 p.e.: 0.159

3.5 p.e.: 0.4445.0 p.e.: 0.832

7.5 p.e.: 0.98611.0 p.e.: 0.999

12.0 p.e.: 1.000

2.0 p.e.: 0.159

3.5 p.e.: 0.4445.0 p.e.: 0.832

7.5 p.e.: 0.98611.0 p.e.: 0.999

12.0 p.e.: 1.000

Amplitude [ADC]1130 1140 1150 1160 1170 1180 1190 1200

Yie

ld

0

50

100

150

200

250

300

350

400310×

SiPM 758

50 ns shaping time

400 fF feedb. capacitance

Fraction of mip events2.0 p.e.: 0.158

3.5 p.e.: 0.4445.0 p.e.: 0.832

7.5 p.e.: 0.98510.0 p.e.: 0.998

12.0 p.e.: 0.999

2.0 p.e.: 0.158

3.5 p.e.: 0.4445.0 p.e.: 0.832

7.5 p.e.: 0.98510.0 p.e.: 0.998

12.0 p.e.: 0.999

2.0 p.e.: 0.158

3.5 p.e.: 0.4445.0 p.e.: 0.832

7.5 p.e.: 0.98510.0 p.e.: 0.998

12.0 p.e.: 0.999

2.0 p.e.: 0.158

3.5 p.e.: 0.4445.0 p.e.: 0.832

7.5 p.e.: 0.98510.0 p.e.: 0.998

12.0 p.e.: 0.999

2.0 p.e.: 0.158

3.5 p.e.: 0.4445.0 p.e.: 0.832

7.5 p.e.: 0.98510.0 p.e.: 0.998

12.0 p.e.: 0.999

2.0 p.e.: 0.158

3.5 p.e.: 0.4445.0 p.e.: 0.832

7.5 p.e.: 0.98510.0 p.e.: 0.998

12.0 p.e.: 0.999

Figure 46: The e ien y in dete ting a mip-like signal is measured at dierent

threshold values (in SiPM photo-ele tron units) operating the hip in low gain

mode at 50 ns shaping time, 200 fF and 400 fF feedba k apa itan e, left and

right panel, respe tively.

17 Con lusions

During 2008 and 2009 systemati studies have been performed to hara terise

the analogue omponent of the SPIROC ASIC, designed for the readout of the

analogue hadroni alorimeter for the international linear ollider proje t. The

more signi ant results are presented and des ribed in this report showing the

39

fullled requirements and the features whi h should be xed in the next ver-

sion of the hip. These measurements have been done on the SPIROC version

SPIROC 1B, whi h has the analogue pro essing of signals almost fully imple-

mented.

The ASIC was shown to handle the dynami range overed by the SiPMs

whi h are expe ted to be readout in both alibration mode for the maximum

ampli ation at 100 fF feedba k apa itan e, and physi s mode for values of

feedba k apa itan e above 400 fF, resulting non-saturated up to ≈ 80 and ≈ 8mips, respe tively. The values reported here refer to a SiPM with pixel gain of

order 0.5 ·106. In ase of SiPMs with highly varying pixel gain (as for the SiPMs

used in the past AHCAL test beam operations), the dynami range overed

by the photodete tor hanges, and the operation mode of the hip should be

hanged a ordingly, resulting in a hange of the signal over noise ratio.

The data a quisition is forseen to run in auto-trigger mode, being a tivated

by the SiPM signals, and the hip appears to full this requirement in the physi s

mode, rea hing 100% trigger e ien y for trigger threshold values above half

a mip. For these values the trigger time walk and jitter were found to be less

than 3 and 1 ns, respe tively. Quite remarkable, is the observed possibility to

t the thermal noise, opening the potentiality of self- alibrating the devi e.

The ele troni noise was investigated and found to be typi ally within one

millivolt, depending on the spe i shaping time and ampli ation setting. The

most sizable additional ontribution to the noise is indu ed by swit hing on the

tra k and hold omponent, approximately doubling the noise. When oupled to

an external signal sour e the noise dependen e on varying the oupling apa i-

tan e (as for real SiPMs) was found to be within 20% in the range 10-100 pF.

Comparing the 36 input hannels, the pedestals showed a spread of 2 mV,

and their deviation due to ross-talk was measured to be within ±0.5 mV in the

investigated range from one to 33 mips (40 pC).

Ea h input SiPM high voltage an be individually tuned via a DAC HV

adjustment dedi ated to ea h dete tor line. The DAC to volt alibration was

performed for all hannels showing a hannel to hannel average variation of

100 mV, and an average maximum deviation to linearity of 80 mV (for some

hannels up to 200 mV). The observed deviation from linearity appears to be

systemati ally reprodu ible, and ould be orre ted for via a proper alibration.

The high-low gain path oupling was studied and a sizable dependen e (up

to 10%) on the high gain ampli ation setting was measured for the physi s

mode readout.

Probably the most surprising feature of the hip was the observed in rease

of the signal peaking time with in reasing inje ted harge, related to properties

of the used tra k and hold swit h. Investigation with simulations by the hip

designers in Orsay is on-going, and a possible ure of the shown feature should

be available in the next generations of the ASIC.

The investigation of the digital omponent of the ASIC, implemented in the

version SPIROC 2, is on going and will be presented in a separate future note.

40

A knowledgments

We are deeply grateful to S. Callier, C. De La Taille, and L. Raux

of the OMEGA group at Orsay, and to F. Sefkow and E. Garutti at

DESY for useful dis ussions and suggestions.

Referen es

[1 J. Brau et al., International Linear Collider Referen e Design Report,

ILC-REPORT-2007-001 (2007).

[2 M. Bou hel et al., Pro . of the IEEE 2008 Nu lear S ien e Symposium,

Dresden, Germany, O tober 2008.

[3 M. Groll, Constru tion and Commissioning of a Hadroni Test-Beam

Calorimeter to Validate the Parti le-Flow Con ept at the ILC, PhD Thesis

2007, DESY-THESIS-2007-018.

[4 N. Feege, Sili on Photomultipliers: Properties and Appli ation in a Highly

Granular Calorimeter, Diploma Thesis 2008, DESY-THESIS-2008-050.

[5 W. R. Leo, Te hniques for Nu lear and Parti le Physi s Experiments,

Springer-Verlag.

[6 E. Kowalski, Nu lear Ele troni s, Springer Verlag.

[7 L. Raux, private ommuni ations.

[8 L. Raux, SPIROC ASIC Measurement, Presentation given at CALICE

ELECTRONICS meeting, Mar h 11, 2008.

41

Documents

W. Shen arXiv:0911.1566v1 [physics.ins-det] 8 Nov …azusa.shinshu-u.ac.jp/~coterra/EBUreferences/Spiroc/0911...y/Pulsar, MEPh tical iden to the devices used in AHCAL test b eam op