OK now need to do working out for the final two stages
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@ -35,6 +35,11 @@ Not a document to be proof read.
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Proof of analysis concept.
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Proof of analysis concept.
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Function $fm$ applied to a component returns its failure modes.
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Function $fm$ applied to a component returns its failure modes.
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The circuits specified are not typical saftey critical circuitry which usually
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has both redundancy and self~checking and/or diagnostic features build in.
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These are examples of the FMMD methodology being applied to some standard electronic circuits.
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\end{abstract}
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\end{abstract}
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\maketitle
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\maketitle
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\tableofcontents
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\tableofcontents
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@ -457,7 +462,7 @@ We merely have to choose a top level event and work down using $XOR$ gates.
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This circuit performs poorly from a safety point of view.
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This circuit performs poorly from a safety point of view.
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Its failure modes could be indistinguishable from valid readings (especially
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Its failure modes could be indistinguishable from valid readings (especially
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wihen it becomes a V2 follower).
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when it becomes a V2 follower).
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\begin{figure}[h]
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\begin{figure}[h]
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\centering
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\centering
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@ -773,10 +778,20 @@ This circuit is described in the Analog Applications Journal~\cite{bubba}.
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The circuit uses four 45 degree phase shifts, and an inverting amplifier to provide
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The circuit uses four 45 degree phase shifts, and an inverting amplifier to provide
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gain and the final 180 degrees of phase shift (making a total of 360 degrees of phase shift).
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gain and the final 180 degrees of phase shift (making a total of 360 degrees of phase shift).
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We identifiy three functional groups, the inverting amplifer (analysed in section~\ref{fig:invamp}),
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From a fault finding perspective this circuit is less than ideal.
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a 45 degree phase shifter (a {$10k\Omega$} resistor and a $10nF$ capacitor) and a noninverting buffer
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The signal path is circular (its a positive feedback circuit) and most failures would simply cause the output to stop oscillating.
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However, FMMD is a bottom -up analysis methodology and we can therefore still identify
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{\fgs} and apply analysis from a failure mode perspective.
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If we were to analyse this circuit without modularisation, we have 14 components with
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($4.4 +10.2 = 36$) failure modes . Applying equation~\ref{eqnrd2} gives a complexity comparison figure of $13.36=468$.
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The reduce the complexity required to analyse this circuit we apply FMMD and start by determining {\fgs}.
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We identify three types functional groups, an inverting amplifier (analysed in section~\ref{fig:invamp}),
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a 45 degree phase shifter (a {$10k\Omega$} resistor and a $10nF$ capacitor) and a non-inverting buffer
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amplifier. We can name these $INVAMP$, $PHS45$ and $NIBUFF$ respectively.
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amplifier. We can name these $INVAMP$, $PHS45$ and $NIBUFF$ respectively.
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We can use these {\fgs} to describe the circuit in block diagram form, as in figure ~\ref{fig:bubbablock}.
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We can use these {\fgs} to describe the circuit in block diagram form, see figure ~\ref{fig:bubbablock}.
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\begin{figure}[h]
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\begin{figure}[h]
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\centering
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\centering
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@ -838,7 +853,7 @@ $$ fm(NIBUFF) = fm(OPAMP) = \{L\_{up}, L\_{dn}, Noop, L\_slew \} $$
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% describe what we are doing, a buffered 45 degree phase shift element
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% describe what we are doing, a buffered 45 degree phase shift element
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\subsection{Bringing the functional Groups Together: The `Bubba' Oscillator.}
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\subsection{Bringing the functional Groups Together: FMMD model of the `Bubba' Oscillator.}
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We could at this point bring all the {\dcs} together into one large functional
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We could at this point bring all the {\dcs} together into one large functional
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group (see figure~\ref{fig:poss1finalbubba})
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group (see figure~\ref{fig:poss1finalbubba})
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@ -848,7 +863,9 @@ The capactior and 180 degree inverting amplifier, form a {\fg}
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providing an amplified 225 degree phase shift, which we can call $PHS225AMP$.
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providing an amplified 225 degree phase shift, which we can call $PHS225AMP$.
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%
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%
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We could also merge the $NIBUFF$ and $PHS45$
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We could also merge the $NIBUFF$ and $PHS45$
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{\dcs} into a {\fg} and the resulant derived component from this we could call a $BUFF45$, and then with those three, form a $PHS135BUFFERED$ functional group -- with the remaining $PHS45$ and the $INVAMP$ in a second group $PHS225AMP$,
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{\dcs} into a {\fg} and the resulant derived component from this we could call a $BUFF45$,
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and then with those three, form a $PHS135BUFFERED$
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functional group---with the remaining $PHS45$ and the $INVAMP$ (re-used from section~\ref{sec:invamp})in a second group $PHS225AMP$---
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and then merge $PHS135BUFFERED$ and $PHS225AMP$ in a final stage (see figure~\ref{fig:poss2finalbubba})
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and then merge $PHS135BUFFERED$ and $PHS225AMP$ in a final stage (see figure~\ref{fig:poss2finalbubba})
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@ -1239,7 +1256,14 @@ in component ${c_i}$, is given by
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\end{equation}
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\end{equation}
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This can be simplified if we can determine the total number of failure modes in the system $K$, (i.e. $ K = \sum_{n=1}^{|G|} {|fm(c_n)|}$);
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This can be simplified if we can determine the total number of failure modes in the system $K$, (i.e. $ K = \sum_{n=1}^{|G|} {|fm(c_n)|}$);
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equation~\ref{eqn:CC} becomes $$ CC(\FG) = K.(|\FG|-1).$$
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equation~\ref{eqn:CC} becomes
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%$$
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\begin{equation}
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\label{eqn:rd2}
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CC(\FG) = K.(|\FG|-1).
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\end{equation}
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%$$
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%Equation~\ref{eqn:rd} can also be expressed as
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%Equation~\ref{eqn:rd} can also be expressed as
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%
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%
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% \begin{equation}
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% \begin{equation}
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@ -5,7 +5,7 @@
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\usepackage{tikz}
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\usepackage{tikz}
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\usetikzlibrary{shapes,snakes}
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\usetikzlibrary{shapes,snakes}
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\usetikzlibrary{shapes.gates.logic.US,trees,positioning,arrows}
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\usetikzlibrary{shapes.gates.logic.US,trees,positioning,arrows}
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\usepackage{subfigure}
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%\usepackage{subfigure}
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\usepackage{amsfonts,amsmath,amsthm}
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\usepackage{amsfonts,amsmath,amsthm}
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\usepackage{algorithm}
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\usepackage{algorithm}
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\usepackage{algorithmic}
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\usepackage{algorithmic}
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