Ciobanu, M.

Deppe, H.

Deppner, I.

Flemming, H.

Frühauf, J.

Herrmann, N.

Kis, M.

Koch, K.

Linev, S.

Loizeau, P.-A.

Manz, S.

Simon, C.

Xiang, C.

GSI Repository

Characterization of the GET4 v1.0 TDC ASIC with detector signals ∗P.-A. Loizeau1, N. Herrmann1, I. Deppner1, C. Simon1, C. Xiang1,2, M. Ciobanu3, H. Deppe3, H.Flemming3, J. Fru¨hauf3, M. Kisˇ3, K. Koch3, S. Linev3, S. Manz4, and the CBM ToF working group1Physikalisches Institut, Universita¨t Heidelberg, Germany; 2Institute of Particle Physics, Central China NormalUniversity, China; 3GSI, Darmstadt, Germany; 4IRI Goethe Universita¨t, Frankfurt, GermanyA free-streaming readout chain is planned for the CBMTime-of-Flight (TOF) wall. The first element in this read-out chain with a difference to usual triggered systems isthe Time to Digital Converter (TDC). The GET4 ASIC is afree-streaming TDC developed for the CBM TOF wall. Af-ter tests with a first version called GET4 Proto, the GET4v1.0 became available at the end of 2012 [1]. It was testedwith pulser first alone [3] and then in conjunction with thePADI-6 pre-amplifier and discriminator ASIC [2].Another interesting option for the TDC in the CBM TOFreadout chain is the development of FPGA-TDCs. A firstprototype for those is the VFTX board. A cosmic irradia-tion test campaign was performed throughout 2013 in Hei-delberg using our last MRPC prototype, PADI-6 cards andVFTX boards to validate the detector design and this TDCoption. Two plastics scintillators readout on both ends byphoto-multipliers provide the efficiency and time reference.Results of the VFTX readout chain are presented in [5]. Inthe current VFTX readout chain, splitter boards are usedbetween the PADI output and the VFTX input to ensureproper LVDS levels of the signals. As pictured in Fig. 1,the GET4 readout chain was connected in parallel for someof the data taking periods using the second output of thesplitters. The GET4 readout chain is composed of 8 GET4v1.0 chips, a Syscore v2 Readout Controller and an ABBPCI-E board for the optical readout. The analysis chain insoftware is the same as in the VFTX case.Figure 1: Connection scheme of the setup used for the cos-mic rays test of GET4 v1.0.A measurement was done with the systems running inparallel at an RPC High Voltage of 11.5 kV. At this highvoltage, the RPC efficiency relative to coincidences of theplastic scintillators reaches 97.5 % in the GET4 system.The system time resolution obtained after all calibrationsis 82 ps. This can, however, be separated into two classesof events: those with multiple TDC hits on at least one RPCchannel, for which the resolution is 90 ps, and those withonly single TDC hits, for which the resolution is 76 ps.∗Work supported by EU/FP7-Hadron Physics 3/WP19, BMBF05PRVHFC7 and DFG GRK 1039This stresses the importance of a proper matching betweenthe components in a free-streaming TOF system to reducefake data from reflexions, noise and cross-talk. When tak-ing only single hit events, a time resolution of 49 ps can beextracted for the RPC and its electronics, by subtracting thecontribution of the reference system. Similar results wereobtained both when using a synchronization signal fromthe triggered system and in free-streaming mode.In parallel to the trigger on coincidences of the two plas-tics, triggers on the OR of the PMTs and on the OR ofthe RPC strips were used to prevent buffer overflows in theVFTX system. This provides the opportunity to extract thetime resolution of the GET4 system in real conditions withquite good statistics. As the time resolution of the VFTXsystems and of the splitter boards are known, this can bedone by comparing the time measured in the VFTX sys-tem to the one measured in the GET4 system. As the timeframes of the two systems are independent, one actuallyneeds to compare the value of time differences measuredin both the VFTX and GET4 systems (Eq. 1).Δt = (tA − tB)GET4 − (tA − tB)V FTX (1)Assuming the jitters of the VFTX, GET4 and splitter areindependent and Gaussian, the GET4 resolution can be ex-tracted for each pair (A,B) of signals (Eq. 2). This pro-cedure was done for the left-right time differences of bothplastics and of the equipped RPC strips. The counts foreach left-right pairs are used to obtain a mean time resolu-tion. The values of time resolution for the other elementsare σV FTX = 12 ps [4] and σSplitter = 10 ps. The meantime resolution for GET4 v1.0 channels on different daugh-ter boards and with RPC signals is then σGET4 = 24 ps.σGET4 channel =√12σ2Δt − σ2V FTX − σ2Splitter (2)These value are within the CBM TOF specifications, butneed to be tested with higher particle fluxes.References[1] H. Flemming et al., CBM Progress Report 2012, Darmstadt2013, p. 70[2] P.-A. Loizeau et al., CBM Progress Report 2012, Darmstadt2013, p. 66[3] J. Fru¨hauf et al., CBM Progress Report 2012, Darmstadt2013, p. 67[4] J. Fru¨hauf et al., CBM Progress Report 2012, Darmstadt2013, p. 71[5] C. Simon et al., “RPC prototype test with cosmic irradiation”,this reportNQM-CBM-24 GSI SCIENTIFIC REPORT 201340 doi:10.15120/GR-2014-1-NQM-CBM-24

Characterization of the GET4 v1.0 TDC ASIC with detector signals

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Characterization of the GET4 v1.0 TDC ASIC with detector signals

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