Adloff, C.

Chefdeville, M.

Espargilière, A.

Gaglione, R.

HAL Université de Savoie

Calibration of Electronic Read-out chains for theMICROMEGAS chambersC. Adloff, M. Chefdeville, A. Espargilie`re, R. GaglioneTo cite this version:C. Adloff, M. Chefdeville, A. Espargilie`re, R. Gaglione. Calibration of Electronic Read-outchains for the MICROMEGAS chambers. 2009, pp.11. <in2p3-00400295v2>HAL Id: in2p3-00400295http://hal.in2p3.fr/in2p3-00400295v2Submitted on 2 Jul 2009HAL is a multi-disciplinary open accessarchive for the deposit and dissemination of sci-entific research documents, whether they are pub-lished or not. The documents may come fromteaching and research institutions in France orabroad, or from public or private research centers.L’archive ouverte pluridisciplinaire HAL, estdestine´e au de´poˆt et a` la diffusion de documentsscientifiques de niveau recherche, publie´s ou non,e´manant des e´tablissements d’enseignement et derecherche franc¸ais ou e´trangers, des laboratoirespublics ou prive´s.   LAPP-TECH-2009-02 March 2009           Calibration of Electronic Read-out chains for the MICROMEGAS chambers    C. Adloff, M. Chefdeville, A. Espargilière, R. Gaglione  LAPP - Université de Savoie - CNRS/IN2P3 BP. 110 F-74941 Annecy-le-Vieux Cedex, FRANCE    Calibration of Electronic Read-out chains for theMICROMEGAS chambersC. Adloff – M. Chefdeville – A. Espargilie`re – R. Gaglioneversion 0.530 juin 20091 CAEN V550This is a CRAM unit coupled to a 10-bit ADC. Its differential inputs are 50 Ω adapted. The gaincan be selected among 4 values. Our setting is 1023 ADU1 for 1.5 V. Two sets of measures have beenperformed, with a DC power supply as input signal. The module tested here is module 4, channel 1. Thesequencer is auto-triggered by acquisition software. The manual indicates that it is a 10-bit ADC with1.5 V dynamic, which leads to 1500/(210 − 1) =1.466 mV/ADU or 0.682 ADU/mV.1.1 Calibration with common mode signal1.1.1 SetupSetup is shown in fig. 1. The signal+ is monitored with a precision voltmeter.+gain controlCRAM+ADC-+signal+50 Ω50 ΩADC−inADC+inCAEN V551BFigure 1 – V550 ADC in common mode1.1.2 Resultssignal+ (mV) ADU0 10150 105250 167500 3261000 6451500 963The corresponding conversion ratio is 1.574 mV/ADU or 0.635 ADU/mV.1Analog to Digital Unit11.2 Calibration with differential mode signal1.2.1 SetupSetup is shown in fig. 2. The signal+, signal− and signal = signal+ − signal− are monitored witha precision voltmeter.+gain controlCRAM+ADC-+signal+50 Ω50 Ω+ADC−inADC+insignal− CAEN V551BFigure 2 – V550 ADC in differential mode1.2.2 Resultssignal+ (mV) signal− (mV) signal (mV) ADU0 0 0 9150 -150 300 200300 -300 600 390500 -500 1000 645750 -750 1500 962The corresponding conversion ratio is 1.574 mV/ADU or 0.635 ADU/mV.The conversion ration of CAEN V550 is 1.574 mV/ADU or 0.635 ADU/mV, either in single-ended or indifferential mode.2 Gassiplex boardFigure 3 shows the general architecture of Gassiplex board, from CEA/IRFU, equipped with 6 Gassi-plex 0.7-3 chip from CERN (only one channel is represented), thus providing 96 analog readout channels.The gain of these chips (and chips only, Vout), in gaseous detector mode, is 3.675 mV/fC (from Gassiplex-+CprotGtestGinCtestint50 ΩRpolGASSIPLEX BOARDG−outG+outCHIPVoutFigure 3 – Gassiplex board2documentation). The board itself has a differential output stage which doubles the signal. The theoricalboard gain is 7.35 mV/fC. In order to measure the gain of these boards, we use an HP pulse generatorwith a precision attenuator (Wavetek). With a ∆V of 400 mV on a 50 Ω resistor, the injected chargesthrough a 1 pF capacitor are :Attenuation (dB) Injected charge (fC)0 400-10 126.5-20 40-30 12.65-40 4-50 1.2652.1 Calibration with internal capacitor2.1.1 SetupEach channel has its own test capacitor Ctestint ≃ 1 pF. Exact value is not very well known, butmatching from channel to channel must be very good. The pulse generator is connected to the test input(Gtest) of Gassiplex board through the attenuator. The relevant differential output voltage (G+out−G−out)is measured on 2 channels of the oscilloscope.0 VG+outG−outsignal+signal−pedestalbaseline−baseline+pedestal−pedestal+ch0 ch3ch2ch1Figure 4 – Gassiplex board differential output signals2.1.2 ResultsThe following results are for board number 42, channel number 3, with 40 fC input charge accordingto fig. 4. The differential output signal on Gout = G+out −G−out. The pedestal, also differential, is definedas pedestal = pedestal+ − pedestal−2. The measure is signal = signal+ − signal− = Gout − pedestal =(G+out − pedestal+)− (G−out − pedestal−). The following table gives the experimental points in mV.2For Catherine : pedestal+ + pedestal− should be equal to zero, but in reality, it is equal to offset.3Qinj (fC) G+out pedestal+ G−out pedestal− signal+ signal− signal40 194 34 -198 -37 160 -161 321The corresponding board gain is 8.025 mV/fC.2.2 Calibration with external capacitor2.2.1 SetupAnother test has been performed with an injection test box (fig. 5), connected at the Gin input ofa Gassiplex board (board 42, channel 3). The Ctestext capacitor in the box has been carefuly measuredat 1.038 pF±1%@1 MHz with a HP4284A LCR meter. The capacitance seems to decrease vs frequency.The pulse from thess generator involves high frequency (several 100 MHz), so it is possible that actualcapacitance is slightly lower.50 ΩCtestextBOXFigure 5 – External injection capacitor in its box2.2.2 ResultsExperimental points are in mV :Qinj (fC) G+out pedestal+ G−out pedestal− signal+ signal− signal41.52 182 35 -186 -39 147 -147 294The corresponding gain is 7.08 mV/fC.2.3 Gassiplex chip gain verificationTo check the chip gain only, the response to a 41.52 fC signal through Ctestext has been measuredwith a 10× passive probe on a Vout node. The following table presents the results.Qinj (fC) Vout (mV) pedestal (mV) signal (mV)41.52 -114 22 -136The corresponding gain is 3.27 mV/fC for the chip only (only one channel tested).2.4 Gassiplex board + CAEN V550 ADCThe theorical gain of a Gassiplex board is 7.35 mV/fC and the theorical conversion factor of theCAEN V550 ADC is 0.682 ADU/mV, thus giving a theorical conversion factor of 5.01 ADU/fC.A similar evaluation can be made with measured values : the measured Gassiplex board gain is7.08 mV/fC and the measured CAEN V550 ADC convertion ratio is 0.635 ADU/mV, giving a conversionfactor of 4.49 ADU/fC.42.5 SetupThe Micromegas detector are polarized with their working high voltage. As the gain of the Gassiplexboards as been verified with an external capacitor, the internal capacitor will be used for these tests.The pulse generator and attenuator values given in 2 have been used. The Gassiplex boards are read byCAEN V550 ADCs. Several NIM counters are used to select the Gassiplex channel to be excited, and togenerate 1 000 pulses for each input charge, i.e. 126.5, 40 and 12.65 fC. For each charge, the ADC counthistogram is fitted with a gaussian and the mean is plotted versus injected charge and a linear functionfitted to the measured points, which gives the conversion ratio (fig. 6).fC20 40 60 80 100 120ADU100200300400500600Figure 6 – ADC Unit versus input charge for one Gassiplex channel (anode readout)2.6 ResultsThe mean conversion ratio over 384 channels (4 boards) is 4.85±0.25 ADU/fC with a standard de-viation of 0.07 ADU/fC. The conversion ratio distribution of one board (96 channels) is given fig. 7.2.7 Important noteAccording to the Gassiplex documentation, a chip gain of 3.675 mV/fC has been performed withan external capacitor, while a similar test with the internal capacitors gives a gain of 3.8 mV/fC. Isuggest to substract 3.29% to 4.85 ADU/fC, the convertion ratio obtained with internal capacitor tomatch the convertion ratio obtained with external capacitor. Thus, the 4.85±0.25 ADU/fC becomes4.69±0.25 ADU/fC.The conversion ratio of a Gassiplex board on a CAEN V550 ADC is 4.69±0.25 ADU/fC3 ORTEC 142C3.1 Theorical valueThe gain of the ORTEC 142C charge preamplifier given in units of MeVin Si is 20 mV/MeV. With anionization potential of 3.6 eV, the charge deposited in Si is about 44.2 fC/MeV, the gain of the preamplifer5GainEntries  96Mean    4.876RMS    0.09631ADU/fC4 4.2 4.4 4.6 4.8 5 5.2 5.4 5.6 5.8 6Counts0510152025Figure 7 – Gain distribution for one Gassiplex boardshould then be 452.5 µV/fC.3.2 SetupBe careful ! The E output of the 142C charge preamplifier is 93 Ω adapted : it must be loadedby an ORTEC spectroscopy amplifier like the ORTEC 570. Additionaly, the T output must be 50 Ωadapted, even if unused (please read the manual). Setup is presented in fig. 8. The accuracy of the 570spectroscopy amplifier gain setting has been verified. Two sets of measures have been performed, eitherwith the regular Oin input associated with the so-called box (containing the external capacitor), eitherwith a pulser directly connected to the Otest test input. In the latter case, the voltage is monitored withan oscilloscope, as the pulse generator is no longer adapted.ORTEC 142CTEOtest93.1 ΩCtestintOin50 Ωgain controlCRAM+ADC-+50 Ω50 ΩCAEN V550ORTEC 570gainV142CV5701 MΩSCOPE1 MΩADC+inpeaking timeFigure 8 – Calibration of the ORTEC 142C charge preamplifier63.3 ResultsWith external capacitor :Qin (fC) ∆V142C (mV) ∆V570 (mV) ADU0 0 0 941.2 14.6 145 100131.3 46 460 298412 146 1440 924With internal capacitor :Qin (fC) ∆V142C (mV) ∆V570 (mV) ADU0 0 0 933.6 12.7 125 88105.6 40.2 394 259336 126 1244 8011048 400 3900 –Experimental data have been fitted with straight line, as shown in fig. 9.3.4 SummaryGain with Cext Gain with Cint142C 0.351±0.004 mV/fC 2.849±0.032 fC/mV 0.378±0.021 mV/fC 2.645±0.147 fC/mV570 3.480±0.071 mV/fC 0.287±0.006 fC/mV 3.713±0.342 mV/fC 0.269±0.024 fC/mVV550 2.359±0.137 ADU/fC 0.424±0.025 fC/ADU 2.199±0.026 ADU/fC 0.455±0.005 fC/ADUThe conversion ratio of the ORTEC 142C+570 and CAEN V550 ADC is 2.199±0.026ADU/fC.4 Detector with 55FeAll subsequent measurements have been performed with the same chamber (β2), gas mixture (Ar-CO2 90-10) and operating voltage (mesh@-510 V and drift@100 V/cm), and are intended for checkingthe measured calibration constants of the ORTEC and Gassiplex chains. They are realized by reading out55Fe signals from the mesh (through the ORTEC chain) and the chamber pads (through the Gassiplexchain) and measuring the charge that corresponds to the photopeak of the 55Fe spectrum. The time T1has been adjusted for each case.4.1 Gassiplex+V550 spectrumThe 55Fe source X-rays convert mainly above 4 adjacent pads. The photopeak position averaged overthe 4 pads is estimated to be at 781.3±1ADU and the pedestal to be at 20ADU (fig. 10). The ADCcount distribution is plotted vs input charge, fitted with a gaussian, and the corresponding means havebeen fitted with y = p0 ·x + p1. With a gain of 4.85±0.25 ADU/fC (Cint), the peak corresponds to157 fC. With a gain of 4.69±0.25 ADU/fC (Cint corrected), the peak corresponds to 162 fC.74.2 142C+570+V550 spectrumThe peak position of the corresponding spectrum is estimated to be at 377.1±1.4ADU and thepedestal to be at 9ADU (fig. 10). With a gain of 2.199±0.026 ADU/fC (Cint), the peak corresponds to167 fC. With a gain of 2.359±0.137ADU/fC (Cext), the peak corresponds to 156 fC.4.3 142C+570+scope spectrumA gain of 3.480±0.07 mV/fC has been formerly established. With the 142C+570+oscilloscope, wehave obtained a peak around 600 mV (fig. 11), i.e. 172.4 fC.The three peak positions in charge are in very good agreement with preceding measurements.8Input charge (fC)0 50 100 150 200 250 300 350 400Ouput voltage (mV)020406080100120140 / ndf 2χ 0.01895 / 2p0        0.00453± 0.3512 p1            0±     0  / ndf 2χ 0.0112 / 2p0        0.02193± 0.3779 p1            0±     0 InternalExternal(a) 142C preamplifierInput charge (fC)0 50 100 150 200 250 300 350 400Ouput voltage (mV)0200400600800100012001400 / ndf 2χ 0.08604 / 1p0        0.0712±  3.48 p1        4.863± 0.6791  / ndf 2χ 0.002609 / 1p0        0.342± 3.713 p1        18.88± 0.3763 InternalExternal(b) 570 amplifierInput charge (fC)0 50 100 150 200 250 300 350 400ADC code (ADU)02004006008001000 / ndf 2χ 0.03442 / 3p0        0.02655± 2.199 p1            0±     9  / ndf 2χ 0.002407 / 3p0        0.1366± 2.359 p1            0±     9 InternalExternal(c) V550 Analog to Digital ConverterFigure 9 – Experimental data and fit results for mesh readout9ADC counts200 400 600 800 1000110210Pads readoutMesh readoutFigure 10 – 55Fe spectrum measured on mesh (ORTEC chain) and pad (Gassiplex) readoutFigure 11 – 55Fe spectrum measured with an oscilloscope10

Calibration of Electronic Read-out chains for the MICROMEGAS chambers

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