TIBTIDNotes/TIBTIDIntNote/SiStripComponents.tex

\section{The Integration Components}
\label{sec:Components}

\subsection{The Silicon Module}

The TIB and TID module\ref{table:modules} consist of a carbon fiber support
frame that holds a single silicon
sensor~\cite{ref:mask}\cite{ref:sensors} and the front-end electronics
hybrid circuit\cite{ref:hybrid}. 
These detectors are produced from individual, 320~$\mu$m thick, sensors.
All silicon strip sensors are of the 
single-sided ``p-on-n'' type
with integrated decoupling capacitors, aluminium readout strips 
and polysilicon bias resistors.
The sensor is aligned with respect to the same frame 
aluminum insets that are used to fix the module the ledges in such a
way the sensor positioning is guaranteed with respect to the support
structure~\cite{ref:assembly}.\\
Double-sided detectors are built by simply assembling two independent
single-sided modules (``R-Phi'' and ``Stereo'') back to back.
The double-sided TIB layers and TID rings are equipped with module
sandwiches capable of a space point measurement and obtained by
coupling back-to-back a $r\phi$ module and a special ``stereo''
module with the sensor tilted by $100\mrad$.
The stereo sensor and electronics are identical to the R-Phi ones, the only
difference being in the support mechanics and pitch adapters. \\


%The stereo module just
%differ from the $r\phi$ one in the details needed to cope with the
%different sensor orientation.
\begin{table}[!htb]
\begin{center}
\caption[smallcaption]{Details on the different TIB/TID modules. }
\label{table:modules}
%\begin{tabular}{|l||c|c|c|c|c|c|c|}
\begin{tabular}{|l|ccccc|}
\hline
 Module & pitch ($\mu$m) &   Assembly &Active area & \# of APVs  & \# of channels    \\  
 type   &                &   type     &$cm^2$      &             & per module        \\
 \hline
% \hline
TIB Layer 1-2 $r-/phi$  & 80      & DS & 35 & 6 & 768 \\
TIB Layer 1-2 stereo    & 80      & DS & 35 & 6 & 768 \\
TIB Layer 3-4 $r-/phi$  & 120     & SS & 35 & 4 & 512 \\
TID Ring 1 $r-/phi$     & 81-119  & DS & 85 & 6 & 768 \\
TID Ring 1 stereo       & 81-119  & DS & 85 & 6 & 768 \\
TID Ring 2 $r-/phi$     & 81-119  & DS & 88 & 6 & 768 \\
TID Ring 2 stereo       & 81-119  & DS & 88 & 6 & 768 \\
TID Ring 3 $r-/phi$     & 123-158 & SS & 79 & 4 & 512 \\
\hline 
\end{tabular} 
\end{center}
\end{table}

%%{\bf FIX ME: descrizione/tabella dei vari tipi di moduli.}

%The readout chip
%pitch (44$\mu$m) is matched to the sensor pitch via an aluminum deposited glass substrate
%fanout circuit (pitch
%adapter). The hybrid circuit, which houses the front-end chips and ancillary
%electronics, is realized using kapton multilayer technology integrating the power and 
%signal cables. \\

A single sided module of the TID ring 3 and a TIB double-sided module 
are shown in Fig.~\ref{fig:moduleds}.

%\begin{figure}[!htb]
%\begin{center}
%  \includegraphics[width=0.60\textwidth]{Figs/moduless.pdf}
%\end{center}
%\caption{A 4 chips TIB single sided module mounted on its transportation carrier.}
%\label{fig:moduless}       % Give a unique label
%\end{figure}

\begin{figure}[!htb]
\begin{center}
  \includegraphics[width=0.3\textwidth, height=0.45\textwidth,angle=90]{Figs/module-R1.pdf}
\hskip 5mm
  \includegraphics[height=0.3\textwidth, width=0.45\textwidth]{Figs/moduleds.pdf}
\end{center}
\caption{A ring 3 TID module (left panel). A TIB double-sided module,
  the ``stereo'' module is visible reflected by a mirror (rigth panel).}
\label{fig:moduleds}       % Give a unique label
\label{fig:moduletid}      
\end{figure}

%\subsection{The Front-end Electronics}
The multilayer kapton hybrid circuit holds the module front-end
electronics consisting of four main components: the readout chips
(APV25) and three ASICs (the Multiplexer, the PLL and the DCU). All
devices are addressed and controlled by a I$^2$C serial bus.\\
The signals coming from each strip are processed by four or six front-end 
readout chips, connected to the silicon sensor strips by means of a glass
substrate pitch-adapter. The APV25~\cite{ref:apv}
is a 128 channel chip built in radiation tolerant 0.25 $\mu$m 
CMOS technology~\cite{ref:radtol}. Each channel consists of a
preamplifier coupled to a CR-RC 50ns shaper. The shaper output is sampled at 40MHz into 
a 192 cells pipeline that allows trigger latencies up to 4$\mu$s.\\
The APV25 can operate in {\it peak mode} or in {\it deconvolution
  mode}. In the former the shaping time is $50\ns$; in the latter, by
  using a deconvolution filter~\cite{ref:deconvolution}, the 
  effective shaping time is 25ns. In addition, there is also the
  possibility to switch on or off an inverter stage which slightly 
  decreases the common mode noise contribution.
%  Standard operation mode for Silicon Sensor is with
%  inverter on.  
%%{\bf FIX ME: ma serve??? Nel seguito non si fa mai menzione dei vari
%%  modi di funzionamento dell'APV - forse da aggiungere nela
%%  descrizione del ped-noi run?}

On receiving a level 1 trigger the APV25 sends out serially
%, at 20MHz rate, 
the 128 analogue signals together with information about the
pipeline address and the chip error status; two APV25 are multiplexed
on a differential line by the Multiplexer chip~\cite{ref:mux}. 
In absence of data to stream out, for synchronization purposes, the
APV issues a 25ns pulse called ``tick mark''
with a period of 70 clock cycles.\\
The PLL chip\cite{ref:pll} allows the clock to be delayed by 1.04ns 
steps, to
compensate for path differences of control signals and for any
electronics delay. The PLL also decodes the trigger signals that are
encoded on the clock line.\\
The Detector Control Unit (DCU) contains an eight-channel ADC,
two constant current sources and a temperature sensor. It
monitors two sets of thermistors, one on the sensor
and one on the hybrid, its own internal temperature, the
silicon sensor bias current and the two (1.25 V and
2.5 V) low voltages. Each DCU has a unique hardware identification 
number (called \textit{DCU Hardware ID}) that can also be read through
the $I^2C$ interface. By means of this number each module has an
unique identification.

\subsection{The Analog Opto Hybrid}

The Analog-Opto Hybrids~\cite{ref:aoh} (AOH) performs the
electrical-to-optical conversion of the electrical signals of the two
or three APV25 pairs, depending on the module type, by means of
radiation hard lasers~\cite{Gill:2005ui}. There is one AOH 
per module, sitting on a ledge glued on the cooling pipe very close to
the front-end hybrid. Multi-mode optical fibers~\cite{ref:opto}
transport the signal to the counting room where the FEDs~\cite{ref:fed} 
convert back the signal to an electrical one and digitize it. 
Each AOH has two or three two meter long pig-tail
optical fibres ending with an optical plug.\\
The electrical signals arrive to the AOH through front-end hybrid 
kapton cable. The AOH is powered by the same cable.
By means of the AOH control logic the laser working parameters GAIN
and BIAS can be set via $I^2C$  control registers.
The GAIN parameter can be used to compensate the loss of signal
on the optical link to the FED input. The GAIN parameter has four
possible values, 0, 1, 2, 3, corresponding to a nominal
gain value of 0.5, 0.75, 1, 1.25, respectively. 
During normal operation, if no damage was done to the line and
ideal connections, it is normally set to 1. 
The BIAS parameter regulates the current threshold for the laser
diodes and can be set in the range 0$\div$127. The optimal value
strongly depends on temperature and also on irradiation.

\subsection{The Control Ring}
\label{fig:ctrlring} 

The control of the modules front-end electronic is implemented by means of a
hierarchical structure organized in groups of modules~\cite{ref:dohm}. Each group is 
controlled by a Communication and Control Unit (CCU) taht represents a
``node'' in a ``token-ring'' formed by several daisy-chained CCUs and
known as {\it control ring}. The control ring is mastered by a Front End
Controller, FEC~\cite{ref:opto}, located outside the experiment by
means of optical signals. The entire TIB and TID contains a total of 110
Control Rings.

\begin{description}
\item[Digital Opto Hybrid Module] The FEC optical signals are converted into electrical signals by two DOHs 
(Digital Opto-Hybrid) that send clock, trigger, and control signals to
the token ring of CCUs. The DOHs are physically located on a board,
Digital Opto Hybrid Module~\cite{ref:dohm} (DOHM), that provides up to
15 ports (7 on the main DOHM board plus 8 on its
secondary extension or AUX) to implement the token ring. Each port
connects the DOHM to a CCU located on the Mother Cable head
via a 26 poles flat cable. 
To cope with possible CCU failures that would affect the entire ring, the
control ring features the so called {\it redundancy} by means of
a  {\it double path} layout, shown in Fig.~\ref{fig:redundancy}.
This design exploits the
two input/output replicas of the CCUs: each CCU is connected to the
two nearby CCUs through the primary circuit (``A'') and to the second
next CCUs through the secondary circuit (``B'') by which a failing CCU
can be bypassed. To cope with the failure either of the last
CCU or of the primary DOH (A), the DOHM holds a ``dummy CCU'' and a
spare DOH (B).
\begin{figure}
\begin{center}
  \includegraphics[width=0.85\textwidth]{Figs/default_redundancy.pdf}
\end{center}
\caption{Scheme of primary and secondary circuit of the ring. }
\label{fig:redundancy}
\end{figure}
If no CCU is connected to a given DOHM port, a special loop-back plug
must be  inserted in order to ensure the continuity of the primary
and secondary control circuits. 
%The redundancy properties of the system 
%are preserved by observing two ``rules'', i.e. a) if an even number of plugs is needed,
%plugs must be organized in  pairs, each pair having the two plugs inserted in consecutive ports, b) 
%if  an odd number of plugs is needed, one plug must be placed in the last DOHM port 
%(before the dummy CCU), and the remaining ones following the previous rule.
\item[CCU] The CCU serves a group of modules and performs the following tasks:
distributes the clock/trigger and the hard reset to the modules;
dispatches the instructions received from the 
FEC to the modules APV25s and the other ASICS via $I^2C$ or
vice-versa, i.e. addresses the readings from the $I^2C$ devices to the FEC.
Each CCU device sits on a CCU-Module (or CCUM) which carries also
buffering chips and a DCU. Each CCU has an hardware address
configurable by means of appropriate solder pads on the CCUM board to
be shorted or not by a SMD pull up resistor. 
%either directed to themselves or to the devices connected to them. The first case is used
%for example to read the Status Register of the CCU or to raise its output PIA reset lines.
%While in the latter case
%commands are translated to the $I^2C$ protocol and forwarded to the 
%other devices located on the sensor modules or AOH; in case of
%a reply from the $I^2C$ device, the reverse process is done by the CCU, which addresses the
%information to the FEC.
\end{description}

\subsection{The Mother Cable}
The  electrical connections between a group of modules served by the
same CCU are done by the {\it Mother Cable}~\cite{ref:mc}, a
multi-layer kapton copper circuit. An example is shown in
Fig.~\ref{fig:fotomc}. The mother cable is mounted on the carbon fiber
support structure underneath the modules. 
The mother cable holds a CCUM and distributes the $I^2C$ serial data (SDA)
and clock (SCL) lines, the hard reset (PIA reset) line and the
clock/trigger to each module.
The mother cable is connected to a Power Supply unit via two sockets
located at the edge and feeds the modules with low voltages (1.25~V,
2.5~V) and the high voltage.

In the TIB the mother cable coincides
with the string, i.e. six modules
(three double sides assemblies) in L1 and L2 and three modules in L3
and L4. In the TID each mother cable serves a 90-degrees sector,
i.e. six modules (three double-sided assemblies) in R1 and R2 and
five modules in R3.

\begin{figure}
\begin{center}
  \includegraphics[width=0.85\textwidth]{Figs/mothercable.pdf}
\end{center}
\caption{A TIB mother cable with module connectors and CCU (top); 
details of the CCU and the connectors at the edge of the MC
(middle); three module assembled string (bottom).}
\label{fig:fotomc}
\end{figure}

Revision:	1.5
Committed:	Mon Apr 27 14:27:03 2009 UTC (16 years ago) by carlo
Content type:	application/x-tex
Branch:	MAIN
Changes since 1.4:	+71 -34 lines
Log Message:	* empty log message *
#	User	Rev	Content
1	carlo	1.5	\section{The Integration Components}
2	sguazz	1.1	\label{sec:Components}
3	lino	1.2
4	sguazz	1.4	\subsection{The Silicon Module}
5	lino	1.2
6	carlo	1.5	The TIB and TID module\ref{table:modules} consist of a carbon fiber support
7	sguazz	1.4	frame that holds a single silicon
8			sensor~\cite{ref:mask}\cite{ref:sensors} and the front-end electronics
9	carlo	1.5	hybrid circuit\cite{ref:hybrid}.
10			These detectors are produced from individual, 320~$\mu$m thick, sensors.
11			All silicon strip sensors are of the
12			single-sided ``p-on-n'' type
13			with integrated decoupling capacitors, aluminium readout strips
14			and polysilicon bias resistors.
15			The sensor is aligned with respect to the same frame
16	sguazz	1.4	aluminum insets that are used to fix the module the ledges in such a
17			way the sensor positioning is guaranteed with respect to the support
18	carlo	1.5	structure~\cite{ref:assembly}.\\
19			Double-sided detectors are built by simply assembling two independent
20			single-sided modules (``R-Phi'' and ``Stereo'') back to back.
21	sguazz	1.4	The double-sided TIB layers and TID rings are equipped with module
22			sandwiches capable of a space point measurement and obtained by
23			coupling back-to-back a $r\phi$ module and a special ``stereo''
24			module with the sensor tilted by $100\mrad$.
25	carlo	1.5	The stereo sensor and electronics are identical to the R-Phi ones, the only
26			difference being in the support mechanics and pitch adapters. \\
27
28	sguazz	1.4
29			%The stereo module just
30			%differ from the $r\phi$ one in the details needed to cope with the
31			%different sensor orientation.
32	carlo	1.5	\begin{table}[!htb]
33			\begin{center}
34			\caption[smallcaption]{Details on the different TIB/TID modules. }
35			\label{table:modules}
36			%\begin{tabular}{\|l\|\|c\|c\|c\|c\|c\|c\|c\|}
37			\begin{tabular}{\|l\|ccccc\|}
38			\hline
39			Module & pitch ($\mu$m) & Assembly &Active area & \# of APVs & \# of channels \\
40			type & & type &$cm^2$ & & per module \\
41			\hline
42			% \hline
43			TIB Layer 1-2 $r-/phi$ & 80 & DS & 35 & 6 & 768 \\
44			TIB Layer 1-2 stereo & 80 & DS & 35 & 6 & 768 \\
45			TIB Layer 3-4 $r-/phi$ & 120 & SS & 35 & 4 & 512 \\
46			TID Ring 1 $r-/phi$ & 81-119 & DS & 85 & 6 & 768 \\
47			TID Ring 1 stereo & 81-119 & DS & 85 & 6 & 768 \\
48			TID Ring 2 $r-/phi$ & 81-119 & DS & 88 & 6 & 768 \\
49			TID Ring 2 stereo & 81-119 & DS & 88 & 6 & 768 \\
50			TID Ring 3 $r-/phi$ & 123-158 & SS & 79 & 4 & 512 \\
51			\hline
52			\end{tabular}
53			\end{center}
54			\end{table}
55	sguazz	1.4
56	carlo	1.5	%%{\bf FIX ME: descrizione/tabella dei vari tipi di moduli.}
57	sguazz	1.4
58			%The readout chip
59			%pitch (44$\mu$m) is matched to the sensor pitch via an aluminum deposited glass substrate
60			%fanout circuit (pitch
61			%adapter). The hybrid circuit, which houses the front-end chips and ancillary
62			%electronics, is realized using kapton multilayer technology integrating the power and
63			%signal cables. \\
64
65	carlo	1.5	A single sided module of the TID ring 3 and a TIB double-sided module
66			are shown in Fig.~\ref{fig:moduleds}.
67	sguazz	1.4
68			%\begin{figure}[!htb]
69			%\begin{center}
70			% \includegraphics[width=0.60\textwidth]{Figs/moduless.pdf}
71			%\end{center}
72			%\caption{A 4 chips TIB single sided module mounted on its transportation carrier.}
73			%\label{fig:moduless} % Give a unique label
74	lino	1.2	%\end{figure}
75
76	sguazz	1.1	\begin{figure}[!htb]
77			\begin{center}
78	sguazz	1.4	\includegraphics[width=0.3\textwidth, height=0.45\textwidth,angle=90]{Figs/module-R1.pdf}
79			\hskip 5mm
80			\includegraphics[height=0.3\textwidth, width=0.45\textwidth]{Figs/moduleds.pdf}
81	sguazz	1.1	\end{center}
82	carlo	1.5	\caption{A ring 3 TID module (left panel). A TIB double-sided module,
83	sguazz	1.4	the ``stereo'' module is visible reflected by a mirror (rigth panel).}
84	sguazz	1.1	\label{fig:moduleds} % Give a unique label
85	lino	1.2	\label{fig:moduletid}
86			\end{figure}
87
88	lino	1.3	%\subsection{The Front-end Electronics}
89	carlo	1.5	The multilayer kapton hybrid circuit holds the module front-end
90			electronics consisting of four main components: the readout chips
91			(APV25) and three ASICs (the Multiplexer, the PLL and the DCU). All
92	sguazz	1.4	devices are addressed and controlled by a I$^2$C serial bus.\\
93	carlo	1.5	The signals coming from each strip are processed by four or six front-end
94			readout chips, connected to the silicon sensor strips by means of a glass
95	sguazz	1.4	substrate pitch-adapter. The APV25~\cite{ref:apv}
96	carlo	1.5	is a 128 channel chip built in radiation tolerant 0.25 $\mu$m
97	sguazz	1.4	CMOS technology~\cite{ref:radtol}. Each channel consists of a
98			preamplifier coupled to a CR-RC 50ns shaper. The shaper output is sampled at 40MHz into
99			a 192 cells pipeline that allows trigger latencies up to 4$\mu$s.\\
100			The APV25 can operate in {\it peak mode} or in {\it deconvolution
101			mode}. In the former the shaping time is $50\ns$; in the latter, by
102			using a deconvolution filter~\cite{ref:deconvolution}, the
103			effective shaping time is 25ns. In addition, there is also the
104	carlo	1.5	possibility to switch on or off an inverter stage which slightly
105			decreases the common mode noise contribution.
106			% Standard operation mode for Silicon Sensor is with
107			% inverter on.
108			%%{\bf FIX ME: ma serve??? Nel seguito non si fa mai menzione dei vari
109			%% modi di funzionamento dell'APV - forse da aggiungere nela
110			%% descrizione del ped-noi run?}
111	sguazz	1.4
112			On receiving a level 1 trigger the APV25 sends out serially
113			%, at 20MHz rate,
114			the 128 analogue signals together with information about the
115			pipeline address and the chip error status; two APV25 are multiplexed
116			on a differential line by the Multiplexer chip~\cite{ref:mux}.
117			In absence of data to stream out, for synchronization purposes, the
118			APV issues a 25ns pulse called ``tick mark''
119			with a period of 70 clock cycles.\\
120	carlo	1.5	The PLL chip\cite{ref:pll} allows the clock to be delayed by 1.04ns
121			steps, to
122	sguazz	1.4	compensate for path differences of control signals and for any
123			electronics delay. The PLL also decodes the trigger signals that are
124			encoded on the clock line.\\
125			The Detector Control Unit (DCU) contains an eight-channel ADC,
126	sguazz	1.1	two constant current sources and a temperature sensor. It
127			monitors two sets of thermistors, one on the sensor
128			and one on the hybrid, its own internal temperature, the
129	lino	1.3	silicon sensor bias current and the two (1.25 V and
130	sguazz	1.4	2.5 V) low voltages. Each DCU has a unique hardware identification
131			number (called \textit{DCU Hardware ID}) that can also be read through
132			the $I^2C$ interface. By means of this number each module has an
133			unique identification.
134
135			\subsection{The Analog Opto Hybrid}
136
137			The Analog-Opto Hybrids~\cite{ref:aoh} (AOH) performs the
138			electrical-to-optical conversion of the electrical signals of the two
139			or three APV25 pairs, depending on the module type, by means of
140			radiation hard lasers~\cite{Gill:2005ui}. There is one AOH
141			per module, sitting on a ledge glued on the cooling pipe very close to
142	carlo	1.5	the front-end hybrid. Multi-mode optical fibers~\cite{ref:opto}
143			transport the signal to the counting room where the FEDs~\cite{ref:fed}
144			convert back the signal to an electrical one and digitize it.
145			Each AOH has two or three two meter long pig-tail
146	sguazz	1.4	optical fibres ending with an optical plug.\\
147	carlo	1.5	The electrical signals arrive to the AOH through front-end hybrid
148	sguazz	1.4	kapton cable. The AOH is powered by the same cable.
149			By means of the AOH control logic the laser working parameters GAIN
150			and BIAS can be set via $I^2C$ control registers.
151			The GAIN parameter can be used to compensate the loss of signal
152			on the optical link to the FED input. The GAIN parameter has four
153			possible values, 0, 1, 2, 3, corresponding to a nominal
154	carlo	1.5	gain value of 0.5, 0.75, 1, 1.25, respectively.
155			During normal operation, if no damage was done to the line and
156	sguazz	1.4	ideal connections, it is normally set to 1.
157			The BIAS parameter regulates the current threshold for the laser
158			diodes and can be set in the range 0$\div$127. The optimal value
159			strongly depends on temperature and also on irradiation.
160	lino	1.2
161	sguazz	1.4	\subsection{The Control Ring}
162	sguazz	1.1	\label{fig:ctrlring}
163	lino	1.3
164	sguazz	1.4	The control of the modules front-end electronic is implemented by means of a
165			hierarchical structure organized in groups of modules~\cite{ref:dohm}. Each group is
166			controlled by a Communication and Control Unit (CCU) taht represents a
167			``node'' in a ``token-ring'' formed by several daisy-chained CCUs and
168			known as {\it control ring}. The control ring is mastered by a Front End
169			Controller, FEC~\cite{ref:opto}, located outside the experiment by
170	carlo	1.5	means of optical signals. The entire TIB and TID contains a total of 110
171	sguazz	1.4	Control Rings.
172
173			\begin{description}
174			\item[Digital Opto Hybrid Module] The FEC optical signals are converted into electrical signals by two DOHs
175			(Digital Opto-Hybrid) that send clock, trigger, and control signals to
176			the token ring of CCUs. The DOHs are physically located on a board,
177			Digital Opto Hybrid Module~\cite{ref:dohm} (DOHM), that provides up to
178			15 ports (7 on the main DOHM board plus 8 on its
179	sguazz	1.1	secondary extension or AUX) to implement the token ring. Each port
180	sguazz	1.4	connects the DOHM to a CCU located on the Mother Cable head
181			via a 26 poles flat cable.
182			To cope with possible CCU failures that would affect the entire ring, the
183			control ring features the so called {\it redundancy} by means of
184	carlo	1.5	a {\it double path} layout, shown in Fig.~\ref{fig:redundancy}.
185			This design exploits the
186	sguazz	1.4	two input/output replicas of the CCUs: each CCU is connected to the
187			two nearby CCUs through the primary circuit (``A'') and to the second
188			next CCUs through the secondary circuit (``B'') by which a failing CCU
189			can be bypassed. To cope with the failure either of the last
190			CCU or of the primary DOH (A), the DOHM holds a ``dummy CCU'' and a
191			spare DOH (B).
192	sguazz	1.1	\begin{figure}
193			\begin{center}
194			\includegraphics[width=0.85\textwidth]{Figs/default_redundancy.pdf}
195			\end{center}
196			\caption{Scheme of primary and secondary circuit of the ring. }
197			\label{fig:redundancy}
198			\end{figure}
199	sguazz	1.4	If no CCU is connected to a given DOHM port, a special loop-back plug
200			must be inserted in order to ensure the continuity of the primary
201			and secondary control circuits.
202			%The redundancy properties of the system
203			%are preserved by observing two ``rules'', i.e. a) if an even number of plugs is needed,
204			%plugs must be organized in pairs, each pair having the two plugs inserted in consecutive ports, b)
205			%if an odd number of plugs is needed, one plug must be placed in the last DOHM port
206			%(before the dummy CCU), and the remaining ones following the previous rule.
207			\item[CCU] The CCU serves a group of modules and performs the following tasks:
208			distributes the clock/trigger and the hard reset to the modules;
209			dispatches the instructions received from the
210			FEC to the modules APV25s and the other ASICS via $I^2C$ or
211			vice-versa, i.e. addresses the readings from the $I^2C$ devices to the FEC.
212			Each CCU device sits on a CCU-Module (or CCUM) which carries also
213			buffering chips and a DCU. Each CCU has an hardware address
214			configurable by means of appropriate solder pads on the CCUM board to
215			be shorted or not by a SMD pull up resistor.
216			%either directed to themselves or to the devices connected to them. The first case is used
217			%for example to read the Status Register of the CCU or to raise its output PIA reset lines.
218			%While in the latter case
219			%commands are translated to the $I^2C$ protocol and forwarded to the
220			%other devices located on the sensor modules or AOH; in case of
221			%a reply from the $I^2C$ device, the reverse process is done by the CCU, which addresses the
222			%information to the FEC.
223			\end{description}
224
225			\subsection{The Mother Cable}
226			The electrical connections between a group of modules served by the
227	carlo	1.5	same CCU are done by the {\it Mother Cable}~\cite{ref:mc}, a
228	sguazz	1.4	multi-layer kapton copper circuit. An example is shown in
229			Fig.~\ref{fig:fotomc}. The mother cable is mounted on the carbon fiber
230			support structure underneath the modules.
231			The mother cable holds a CCUM and distributes the $I^2C$ serial data (SDA)
232			and clock (SCL) lines, the hard reset (PIA reset) line and the
233			clock/trigger to each module.
234			The mother cable is connected to a Power Supply unit via two sockets
235			located at the edge and feeds the modules with low voltages (1.25~V,
236			2.5~V) and the high voltage.
237
238			In the TIB the mother cable coincides
239			with the string, i.e. six modules
240			(three double sides assemblies) in L1 and L2 and three modules in L3
241			and L4. In the TID each mother cable serves a 90-degrees sector,
242			i.e. six modules (three double-sided assemblies) in R1 and R2 and
243			five modules in R3.
244	sguazz	1.1
245	sguazz	1.4	\begin{figure}
246			\begin{center}
247			\includegraphics[width=0.85\textwidth]{Figs/mothercable.pdf}
248			\end{center}
249	carlo	1.5	\caption{A TIB mother cable with module connectors and CCU (top);
250			details of the CCU and the connectors at the edge of the MC
251			(middle); three module assembled string (bottom).}
252	sguazz	1.4	\label{fig:fotomc}
253			\end{figure}
254	sguazz	1.1