EV6_HW_Imp/doc/reflection/main.tex

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\title{
    Reflection experiment\linebreak
    \large{EV6 - Hardware Implementation}
}

\author{
    van Iterson, Arne\\
    Student Nr: 1798423
    \and
    Selier, Tom\\
    Student Nr: 1808444
}

\makeindex

\begin{document}
\maketitle

\begin{abstract}
    This document describes the process of, and measurements taken during the reflection experiment; Part of the EV6 Hardware Implementation course at the University of applied sciences Utrecht.
\end{abstract}

\noindent\makebox[\linewidth]{\rule{\linewidth}{0.4pt}}
\setlist[itemize]{itemjoin=\hspace*{\fill},itemjoin*=\hspace*{\fill}}

\begin{multicols}{2}
    \section{Introduction}
    Signals travel over transmission lines, these lines can be as simple as a wire or as complex as a PCB trace. Any transmission line has a characteristic impedance, when the line is not terminated properly, reflections will occur. 
    These reflections can cause signal integrity issues, and can even damage the transmission hardware. 
    However, the effect can also be used to our advantage, by putting a pulse on the line and measuring the time it takes for the reflection to return, we can roughly calculate the length of the transmission line or a fault in the cable.

    Different termination methods and values have different effects on the reflections. 

    \subsection{Objective}
    The purpose of the experiment is to learn the importance of proper termination of transmission lines. The results should include the effects of various different termination methods and the estimated length of an un-terminated transmission line of unknown length. 
    
    \section{Methodology}
    The experiment requires a pulse to be generated on the line and a way to measure any reflections, the equipment used is as follows:
    \begin{itemize}[beginpenalty=10000]
        \item Rigol DG 2041A Function/Arbritrary Waveform Generator
        \begin{itemize}
            \item Setup according to the method described in the lab manual:
            \begin{itemize}
                \item Pulse 0 to 5 Volts
                \item Frequency 1 kHz
                \item Pulse width 12 ns, edge time 5 ns
                \item Output impedance 50 Ohm
            \end{itemize}
        \end{itemize}

        \item DPO 2012 Oscilloscope
        \begin{itemize}
            \item Using default settings
        \end{itemize}
        \item Multiple 1 meter BNC cables with a characteristic impedance of 50 Ohm
        \begin{itemize}
            \item One for trigger output, three for the experiment itself
        \end{itemize}
        \item BNC cable of unknown length with a characteristic impedance of 75 Ohm
        \item 50 Ohm terminator
        \item Various BNC connectors
        \begin{itemize}
            \item T-connectors
            \item Male to male connectors
        \end{itemize}
    \end{itemize}

    \subsection{Setup}
    All measurements will be taken using the setup in Figure \ref*{fig:setup}.
    \begin{figure}[H]
        \includegraphics[width=\linewidth]{./img/setup.png}
        \caption{Measurement setup}
        \label{fig:setup}
    \end{figure}

    In initial tests, it was found that using a single BNC cable between the terminator and the function generator would produce a reflection, however it would overlap with the original signal, making it difficult to take any measurements. Therefore the setup was built using three cables instead of one in order to delay the reflection to a point where it can be measured. The cables were connected using BNC male to male connectors, making the total cable length about 3 meters. 

    \subsection{Measurements to be taken}
    The following scenarios will be tested:
    \begin{itemize}
        \item Open termination
        \item Short termination
        \item Matched termination
    \end{itemize}
    For each scenario, the full dataset of the oscilloscope will be saved to CSV and analysed at a later moment using Python. 

    \section{Expected results}
    We expect the following results for the different termination methods:
    \begin{description}
        \item[Open termination]
        The reflected signal will be equal in amplitude to the input signal.
        \begin{figure}[H]
            \includegraphics[width=\linewidth]{./img/Graph - Expected - Unterminated.png}
            \caption{Expectation for open termination}
            \label{fig:expected_open}
        \end{figure}

        \item[Short termination]
        The reflected signal will be equal in amplitude to the input signal, but inverted.
        \begin{figure}[H]
            \includegraphics[width=\linewidth]{./img/Graph - Expected - Terminated 0 Ohm.png}
            \caption{Expectation for short termination}
            \label{fig:expected_short}
        \end{figure}
        
        \item[Matched termination]
        The reflected signal will not exist. 
        \begin{figure}[H]
            \includegraphics[width=\linewidth]{./img/Graph - Expected - Terminated 50 Ohm.png}
            \caption{Expectation for matched termination}
            \label{fig:expected_matched}
        \end{figure}

    \end{description}
    \section{Results}
    First, the pulse itself was measured without any cable to ensure that the pulse matched the settings of the function generator. 

    \begin{figure}[H]
        \includegraphics[width=\linewidth]{./img/Graph - Probe Only.png}
        \caption{Pulse measurement, no cable}
        \label{fig:probe_only}
    \end{figure}

    \subsection{Open termination}
    \begin{figure}[H]
        \includegraphics[width=\linewidth]{./img/Graph - Unterminated End.png}
        \caption{Result for open termination}
        \label{fig:actual_open}
    \end{figure}

    \subsection{Short termination}
    \begin{figure}[H]
        \includegraphics[width=\linewidth]{./img/Graph - Terminated 0 Ohm.png}
        \caption{Result for short termination}
        \label{fig:actual_short}
    \end{figure}

    \subsection{Matched termination}
    \begin{figure}[H]
        \includegraphics[width=\linewidth]{./img/Graph - Terminated 50 Ohm.png}
        \caption{Result for matched termination}
        \label{fig:actual_matched}
    \end{figure}

    \subsection{Unknown cable length}
    \begin{figure}[H]
        \includegraphics[width=\linewidth]{./img/Graph - 75 Ohm cable.png}
        \caption{Result for unknown cable}
        \label{fig:unknown_cable}
    \end{figure}

    \section{Conclusion}
    Reflection = bad, termination = good.
\end{multicols}
\end{document}