\documentclass{article}
    \usepackage{tikz}
        \usetikzlibrary{%
            automata,%
            positioning%
        }
    \usepackage{pgfplots}
\begin{document}
    \begin{tikzpicture}

        \begin{axis}[
            at={(5cm,2cm)},         % if you don't want it at (0,0)
            anchor=south west,      % with the corresponding anchor
            %
            width=7cm,
            xtick=\empty,
           % ytick=\empty,
            name=plot
        ]
            \addplot+[blue,ycomb] coordinates { (0,0) (1,1) };
        \end{axis}

        \node[state,xshift=2cm,above=of plot.north]
            (IR320)   {Impulsantwort ($F_s = 320$ MHz)};

        \draw [ultra thick, red] (IR320.center) -- (plot.center);
        \draw [ultra thick,green]            (IR320)        -- (plot);     % why to plot.outer north west?

    \end{tikzpicture}

\makeatletter
\pgfpointborderrectangle{\pgf@x =0.0pt \pgf@y =164.66724pt }{\pgfqpoint {174.01279pt}{127.18533pt}}
\message{it is \the\pgf@x,\the\pgf@y^^J}%

\end{document}

