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[dmems12.git] / dmems12.tex

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@@ -71,24 +71,95 @@
 
 \section{Introduction}
 
 
 \section{Introduction}
 

-Cantilevers  are  used  inside  atomic  force  microscope  which  provides  high
+Cantilevers  are  used  inside  atomic  force  microscope (AFM) which  provides  high

 resolution images of  surfaces.  Several technics have been  used to measure the
 displacement  of cantilevers  in litterature.   For example,  it is  possible to
 resolution images of  surfaces.  Several technics have been  used to measure the
 displacement  of cantilevers  in litterature.   For example,  it is  possible to

-determine  accurately   the  deflection  with   optic  interferometer~\cite{CantiOptic89},
-pizeoresistor~\cite{CantiPiezzo01}                 or                 capacitive
-sensing~\cite{CantiCapacitive03}.
-%% blabla +
+determine  accurately  the  deflection  with different  mechanisms. 
+In~\cite{CantiPiezzo01},   authors  used   piezoresistor  integrated   into  the
+cantilever.   Nevertheless this  approach  suffers from  the  complexity of  the
+microfabrication  process needed  to  implement the  sensor  in the  cantilever.
+In~\cite{CantiCapacitive03},  authors  have  presented an  cantilever  mechanism
+based on  capacitive sensing. This kind  of technic also  involves to instrument
+the cantiliver which result in a complex fabrication process.
+
+In this  paper our attention is focused  on a method based  on interferometry to
+measure cantilevers' displacements.  In  this method cantilevers are illuminated
+by  an optic  source. The  interferometry produces  fringes on  each cantilevers
+which enables to  compute the cantilever displacement.  In  order to analyze the
+fringes a  high speed camera  is used. Images  need to be processed  quickly and
+then  a estimation  method is  required to  determine the  displacement  of each
+cantilever.  In~\cite{AFMCSEM11},  the authors have  used an algorithm  based on
+spline to estimate the cantilevers' positions.
+
+   The overall  process gives
+accurate results  but all the computation  are performed on  a standard computer
+using labview.  Consequently,  the main drawback of this  implementation is that
+the computer is a bootleneck in the overall process. In this paper we propose to
+use a  method based on least  square and to  implement all the computation  on a
+FGPA.
+
+The remainder  of the paper  is organized as  follows. Section~\ref{sec:measure}
+describes  more precisely  the measurement  process. Our  solution based  on the
+least  square   method  and   the  implementation  on   FPGA  is   presented  in
+Section~\ref{sec:solus}.       Experimentations      are       described      in
+Section~\ref{sec:results}.  Finally  a  conclusion  and  some  perspectives  are
+presented.
+
+
+

 %% quelques ref commentées sur les calculs basés sur l'interférométrie
 
 \section{Measurement principles}
 \label{sec:measure}
 
 %% quelques ref commentées sur les calculs basés sur l'interférométrie
 
 \section{Measurement principles}
 \label{sec:measure}
 

+
+
+
+
+
+
+

 \subsection{Architecture}
 \label{sec:archi}
 %% description de l'architecture générale de l'acquisition d'images
 %% avec au milieu une unité de traitement dont on ne précise pas ce
 %% qu'elle est.
 
 \subsection{Architecture}
 \label{sec:archi}
 %% description de l'architecture générale de l'acquisition d'images
 %% avec au milieu une unité de traitement dont on ne précise pas ce
 %% qu'elle est.
 

+In order to develop simple,  cost effective and user-friendly cantilever arrays,
+authors   of    ~\cite{AFMCSEM11}   have   developped   a    system   based   of
+interferometry. In opposition to other optical based systems, using a laser beam
+deflection scheme and  sentitive to the angular displacement  of the cantilever,
+interferometry  is sensitive  to  the  optical path  difference  induced by  the
+vertical displacement of the cantilever.
+
+The system build  by authors of~\cite{AFMCSEM11} has been  developped based on a
+Linnick     interferomter~\cite{Sinclair:05}.    It     is     illustrated    in
+Figure~\ref{fig:AFM}.  A  laser diode  is first split  (by the splitter)  into a
+reference beam and a sample beam  that reachs the cantilever array.  In order to
+be  able to  move  the cantilever  array, it  is  mounted on  a translation  and
+rotational hexapod  stage with  five degrees of  freedom. The optical  system is
+also fixed to the stage.  Thus,  the cantilever array is centered in the optical
+system which  can be adjusted accurately.   The beam illuminates the  array by a
+microscope objective  and the  light reflects on  the cantilevers.  Likewise the
+reference beam  reflects on a  movable mirror.  A  CMOS camera chip  records the
+reference and  sample beams which  are recombined in  the beam splitter  and the
+interferogram.   At the  beginning of  each  experiment, the  movable mirror  is
+fitted  manually in  order to  align the  interferometric  fringes approximately
+parallel  to the cantilevers.   When cantilevers  move due  to the  surface, the
+bending of  cantilevers produce  movements in the  fringes that can  be detected
+with    the    CMOS    camera.     Finally    the    fringes    need    to    be
+analyzed. In~\cite{AFMCSEM11}, the authors used a LabView program to compute the
+cantilevers' movements from the fringes.
+
+\begin{figure}    
+\begin{center}
+\includegraphics[width=\columnwidth]{AFM}
+\end{center}
+\caption{schema of the AFM}
+\label{fig:AFM}   
+\end{figure}
+
+

 %% image tirée des expériences.
 
 \subsection{Cantilever deflection estimation}
 %% image tirée des expériences.
 
 \subsection{Cantilever deflection estimation}


@@ -162,6 +233,29 @@ $3000$ operations.
 
 \subsection{FPGA constraints}
 
 
 \subsection{FPGA constraints}
 

+A field-programmable gate  array (FPGA) is an integrated  circuit designed to be
+configured by  the customer.  A hardware  description language (HDL)  is used to
+configure a  FPGA. FGPAs are  composed of programmable logic  components, called
+logic blocks.  These blocks can be  configured to perform simple (AND, XOR, ...)
+or  complex  combinational  functions.    Logic  blocks  are  interconnected  by
+reconfigurable  links. Modern  FPGAs  contains memory  elements and  multipliers
+which enables to simplify the design and increase the speed. As the most complex
+operation operation on FGPAs is the  multiplier, design of FGPAs should not used
+complex operations. For example, a divider  is not an available operation and it
+should be programmed using simple components.
+
+FGPAs programming  is very different  from classic processors  programming. When
+logic block are programmed and linked  to performed an operation, they cannot be
+reused anymore.  FPGA  are cadenced slowly than classic  processors but they can
+performed pipelined as  well as pipelined operations. A  pipeline provides a way
+manipulate data quickly  since at each clock top to handle  a new data. However,
+using  a  pipeline  consomes more  logics  and  components  since they  are  not
+reusable,  nevertheless it  is probably  the most  efficient technique  on FPGA.
+Parallel  operations   can  be  used   in  order  to  manipulate   several  data
+simultaneously. When  it is  possible, using  a pipeline is  a good  solution to
+manipulate  new  data  at  each  clock  top  and  using  parallelism  to  handle
+simultaneously several data streams.
+

 %% contraintes imposées par le FPGA : algo pipeline/parallele, pas d'op math complexe, ...
 
 
 %% contraintes imposées par le FPGA : algo pipeline/parallele, pas d'op math complexe, ...
 
 


@@ -334,9 +428,9 @@ Finally, the whole summarizes in an algorithm (called LSQ in the following) in t
 
 \subsubsection{Comparison}
 
 
 \subsubsection{Comparison}
 

-\subsection{VDHL design paradigms}
+\subsection{VHDL design paradigms}

 
 

-\subsection{VDHL implementation}
+\subsection{VHDL implementation}

 
 \section{Experimental results}
 \label{sec:results}
 
 \section{Experimental results}
 \label{sec:results}