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\author{Carlos Gil Soriano\\BE-CO-HT\\
\href{mailto:carlos.gil.soriano@cern.ch}{\textbf{\textit{carlos.gil.soriano@cern.ch}}}}
\title{\textbf{{\LARGE Blocking Output Shape for CTDAH board}}}
\date{\today}

\begin{document}

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\paragraph{System Description and Purpose}
The aim of this document is defining the Blocking output shape of the Pulse
Converter Unit. This shape is compatible with previous versions, depending
upon its use.

\pagebreak

{\Large \textbf{History of changes}}\\

This document version has been checked by:\\

This document version has been approved by:\\
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\textbf{Date} & \textbf{Pages} & \textbf{Changes}\\ 
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 \today & All & Initial submission\\
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&&\\
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&&\\
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\section{Boards and compatibility}

Five Pulse Conversion boards from TTL and inverted-TTL -a.k.a. /TTL- to Blocking
are known be working at CERN. Three of them were reported and studied by W. Heinze
\cite{HeinzeReport}\footnote{In this document $t_P$ of the Level Adapter is said
to be the same as the input signal. This is wrong, as it is fixed at 1
$\mu{}s$ \cite{ClaudeDoc}.}. Apart from these three boards, two more are
actually running in CERN facilities: an 8 channel repeater and a 16 channel one.

The table below shows the main parameters of the repetitors:
\begin{center}
\begin{tabular}{|c|c|c|}
\hline
\textbf{Board} & \textbf{Input Level} & \textbf{Output Level}\\
\hline
& TTL &\\
8 Channel Repeater & inverted-TTL & high level: 24V or 30V\\
& high level: 10V to 30V & $t_P$ $\in$ [1.2 $\mu${}$s$, 1.4 $\mu${}$s$]\\
\hline
\hline
& TTL &\\
16 Channel Repeater & inverted-TTL & high level: 24V or 30V\\
& high level: 10V to 30V& $t_P$ $\in$ [1.2 $\mu{}s$, 1.4 $\mu{}s$]\\
\hline
\hline
LASB-TTL-BLO & TTL &high level: 11V or 23V\\
& inverted-TTL & $t_P$ $\approx$ 1.5 $\mu{}s$\\
\hline
\hline
& &high level: 18V or 35V\\
LAPF-TTL-BLO & TTL & $t_P$ $\geq$ 3.5 $\mu{}s$\\
& inverted-TTL & \textbf{SAC/LAF boards}\\
&& \textbf{requirement}\\
\hline
\hline
Level Adapter & TTL & high level: 18V or 35V\\
& inverted-TTL & $t_P$ = 1$\mu{}s$\\
\hline
\end{tabular}
\end{center}

None of the boards specify the design value of the rise time. Only the trailing
edge is reported for LAPF when the circuit is unloaded \cite{HeinzeLAPF}: 0.3
$ms$. Measurements on both 8 and 16 Channel Repeater show a worst rise/fall time
of 120 $\mu{}s$ when the outputs are loaded with 50 \Omega.

\subsection{Uses of boards}
The boards are used as:
\begin{itemize}
  \item \textbf{Repetitors}
  The 8 and 16 Channel Repeaters, LASB and Level Adapter are used as repetitors.
  \item \textbf{Control signal}
  LAPF is intended to interface VME SAC/LAF boards.
\end{itemize}

\pagebreak
\section{Definition of Output shape: Blocking signal}
As it was shown in the previous section, a wide variety of output shapes are
running together. Two types of output shapes will be defined to set a reference
for the design of the new CTDAH board.
\subsection{Criteria}
The criteria employed to define the output shape is as follows:
\begin{center}
\textit{A board designed for a specific use should be backwards compatible with
existing boards so as to avoid interoperability failure.}
\end{center}
As two uses are reported, two specifications are defined.

\subsubsection{Repetitor Boards}
Both \textbf{8 and 16 channel repeaters} are underpinned in the same individual
channel repetitor circuit. This circuit can accept TTL, inverter-TTL and high level
pulses. The main limitation resides in the \textbf{high level of the input
pulse}: it must be \textbf{higher than 10V}.

To comply with previous designs, the definition for this kind of boards,
\textbf{loaded with 50 $\Omega{}$}, is as follows:
\begin{center}
\begin{tabular}{|c|c|c|}
\hline
\textbf{Parameter} & \textbf{Name} &\textbf{Value} \\
\hline
\hline
$v_{i,H}$ & High level & 24V \pm 1V\\
\hline
\hline
$t_{P_{min}}$&\textit{Minimum pulse width} & 1 $\mu{}s$\\
\hline
$t_{P}$&\textit{Typical pulse width} & 1.2 $\mu{}s$\\
\hline
$t_{P_{max}}$&\textit{Maximum pulse width} & 10 $\mu{}s$\\
\hline
\hline
$t_{r}$&\textit{Rise time} & 100 $ns$ \pm 50 $ns$\\
\hline
\hline
$t_{f}$&\textit{Fall time} & 100 $ns$ \pm 50 $ns$\\
\hline

\end{tabular}
\end{center}

\subsubsection{SAC/LAF interfacing boards}
If a board has to interface with a SAC or LAF board, a requirement of the pulse
width longer than 3.5 $\mu{}s$ exists:
\begin{center}
\begin{tabular}{|c|c|c|}
\hline
\textbf{Parameter} & \textbf{Name} &\textbf{Value} \\
\hline
\hline
$v_{i,H}$ & High level & 24V \pm 1V\\
\hline
\hline
$t_{P_{min}}$&\textit{Minimum pulse width} & 3.5 $\mu{}s$\\
\hline
$t_{P}$&\textit{Typical pulse width} & 4.5 $\mu{}s$\\
\hline
$t_{P_{max}}$&\textit{Maximum pulse width} & 10 $\mu{}s$\\
\hline
\hline
$t_{r}$&\textit{Rise time} & 200 $ns$ \pm 50 $ns$\\
\hline
\hline
$t_{f}$&\textit{Fall time} & 200 $ns$ \pm 50 $ns$\\
\hline
\end{tabular}
\end{center}

\pagebreak
\section{Circuit topology chosen}
The circuit topology must be able to be:
\begin{itemize}
  \item Adjusted for use as Repetitor Board.
  \item Adjusted for use as SAC/LAC interfacing Board.
  \item Easily repairable.
\end{itemize}
Considering the three aspects, a monostable blocking oscillator is a worse
option than a flyback topology because of the following reasons:

\subsection{Ease of replacement}
Firstly, the blocking oscillator requires a three winding
transformer, that it is more difficult to replace and more expensive than the
1:1 flyback's one.

Secondly, for obtaining an optimal low-to-high edge of around one tenth of the
pulse rise \cite{BlockingDoc}, a specific turns-ratio transformer must be
used. This design requirement adds more difficulties in the task of choosing a
suitable candidate in case the transformer is no longer produced.

\subsection{Power considerations}
A Power MOSFET \cite{FlybackDoc} is able to better handle the pulsed
power than a BJT.

\subsection{Pulse Shaping}
Lastly, the monostable behaviour of blocking oscillator is not a plus for CTDAH
board. CTDAH is intended to be more customizable in terms of pulse shaping than
previous boards. As the blocking oscillator can only be triggered by a control
signal to produce a pulse of fixed width, the lack of flexibility is
evident.\\
On the other hand, the flyback circuit relies on a control signal that
shapes the pulse width of the output pulse. Thanks to this signal, a CTDAH
channel can be set to work as a repetitor or to provide a control
signal for a SAC or LAF board. It must be noted that, parameters such as the
rise and fall times, rely on physical constraints not modifiable by a control
signal. This is the case of the leakage inductance of a transformer, which slows
down both the rise and falling edges. Transformers with smaller values of
primary inductance will typically have less leakage inductance, hence, they will
be better as repetitors. Transformers with higher values of primary inductance
will be able to produce wider pulses without reaching the its saturation
current. Thus, this second type of transformers should be used when interfacing
with SAC and LAF boards.

\pagebreak
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