source: trunk/MagicSoft/TDAS-Extractor/Introduction.tex@ 5708

\section{Introduction}

\begin{itemize}
\item{Short description of the MAGIC read-out system}
\end{itemize}

Figure~\ref{fig:MAGIC_read-out_scheme} shows a sketch of the MAGIC read-out scheme, including the PMT camera, 
the analog-optical link, the majority trigger logic and 
FADCs. The used PMTs provide a very fast 
response to the input light signal. The response of the PMTs to sub-ns input light pulses shows a FWHM of 
1.0 - 1.2 ns and rise and fall times of 600 and 700 ps correspondingly \cite{Magic-PMT}. By modulating VCSEL 
type laser diodes in amplitude, the fast analogue signals from the PMTs are transferred via 162\,m long, 
50/125\,$\mu$m diameter optical fibers to the counting house \cite{MAGIC-analog-link-2}. After transforming the 
light back to an electrical signal, the original PMT pulse has a FWHM of about 2.2 ns and rise and fall 
times of about 1\,ns. % was 2.2 ns

%an analog optical link \ci
%te{MAGIC-analog-link-2} to the counting house.


\begin{figure}[h!]
\begin{center}
\includegraphics[width=\textwidth]{Magic_readout_scheme1.eps}
\end{center}
\caption[Current MAGIC read-out scheme.]{Current MAGIC read-out scheme: the analog PMT signals are 
transferred via an analog optical link to the counting house where after the trigger decision the signals 
are digitized by using a 300 MHz FADCs system and written to the hard disk of a DAQ PC.} 
\label{fig:MAGIC_read-out_scheme}
\end{figure}

 

%After modulating VCSEL type laser diodes, after traveling through 162m of multi-mode graded index fiber of 50/125 $\mu$m diameter and.


In order to sample this pulse shape with the used 300 MSamples/s FADC system, the pulse is shaped to a 
FWHM greater than 6\,ns 
(the original pulse is folded with a stretching function of 6ns). Because the MAGIC FADCs have a 
resolution of 8 bit only, the signals are split into two branches with gains differing by a factor 10. 
One branch is delayed by 55\,ns and then both branches are multiplexed and consecutively read-out by one FADC.
Figure~\ref{fig:pulpo_shape_high} shows a typical average of identical input signals.
% The maximum sustained trigger rate could be 1 kHz. The FADCs feature a FIFO memory which allows a significantly higher short-time rate.
% Obviously by doing this, more LONS is integrated and thus the performance of the telescope on the analysis level is degraded. 

\par

\ldots {\textit{STILL MISSING:} \ldots
\begin{itemize}
\item DAQ jumps
\item clock noise
\end{itemize}

} \ldots


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