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2 | \subsection{Smart-photodetector electronics} |
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3 | \label{sec:photo} |
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4 | % |
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5 | The coverage of large areas (around 17,500 m$^2$ for MEMPHYS) with |
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6 | photodetectors at lowest cost implies a readout integrated electronics |
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7 | circuit (called ASIC). This makes it possible to integrate: high-speed |
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8 | discriminator on the single photoelectron (pe), the |
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9 | digitisation of the charge on 12 bits ADC to provide numerical signals |
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10 | on a large dynamical range (200~pe), the digitisation of time on 12 |
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11 | bits TDC to provide time information with a precision of 1~ns, and |
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12 | channel-to-channel gain adjustment to homogenize the response of the |
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13 | photomultipliers and to thus use a common high voltage. Such an ASIC |
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14 | for readout electronics allows moreover a strong reduction of the |
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15 | costs, as well as external components (high-voltage units, cables of |
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16 | great quality...) since the electronics and the High Voltage may be |
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17 | put as close as possible to the PMTs and the generated numerical |
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18 | signals are directly usable by trigger logical units and |
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19 | the data acquisition computers (Fig.~\ref{fig:MEMPHYSPMTS}). |
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20 | % |
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21 | |
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22 | The main difficulty in associating very fast analog electronics and |
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23 | digitization on a broad dynamic range does not make it possible yet to |
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24 | integrate all these functions in only one integrated circuit, but |
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25 | certain parts were already developed separately as for example in the |
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26 | OPERA Read Out Channel \cite{Lucotte:2004mi} |
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27 | (Fig.~\ref{fig:OPERAROC}). The evolution of integrated technologies, |
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28 | in particular BiCMOS SiGe 0.35$\mu$m, now make it possible to consider |
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29 | such circuits and has triggered a new campaign of research and |
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30 | development. |
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31 | |
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32 | \begin{figure}[htb] |
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33 | \begin{minipage}[c]{0.44\textwidth} |
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34 | \centering |
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35 | \includegraphics[width=0.85\textwidth]{./figures/ModuleArriere.eps} |
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36 | \caption{\label{fig:MEMPHYSPMTS} |
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37 | \it Sketch of a possible photosensor basic module composed of a matrix |
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38 | of $4\times4$ 12" PMTs with the electronic box containing the High |
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39 | Voltage unit and the Readout chip.} |
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40 | \end{minipage} |
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41 | % |
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42 | \begin{minipage}[c]{0.04\textwidth} |
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43 | ~ |
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44 | \end{minipage} |
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45 | % |
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46 | \begin{minipage}[c]{0.44\textwidth} |
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47 | \centering |
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48 | \includegraphics[width=\textwidth]{./figures/electronic.eps} |
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49 | \caption{\label{fig:OPERAROC} |
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50 | \it Sketch of the existing Read Out electronics developed for the |
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51 | OPERA Target Tracker and that is intented to be extended for MEMPHYS |
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52 | by integrating the ADC and TDC.} |
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53 | \end{minipage} |
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54 | \end{figure} |
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55 | % |
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56 | |
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57 | \newpage |
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58 | |
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59 | |
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