%!tikz editor 1.0
\documentclass{article}
\usepackage{tikz}
\usepackage[graphics, active, tightpage]{preview}
\usepackage{circuitikz}
\PreviewEnvironment{tikzpicture}

%!tikz preamble begin
%\usetikzlibrary{circuits.logic.US, positioning}
\usepackage{circuitikz}
\usepackage[utf8]{inputenc}
%!tikz preamble end


\begin{document}
%!tikz source begin
\begin{tikzpicture}[scale=6,transform shape]
\ctikzset{
    logic ports=ieee,
    logic ports/scale=1,
%    logic ports/fill=lightgray
	% Koordinaten für Kreuzpunkte
 }
\coordinate (A) at (2.75,0.5);
	\fill (A) circle (1.5pt);
	
	% Eingangsvariablen
	\node (x2) at (0.15,0.225) {b};
	\node (x1) at (0.15,0.775) {a};
		
	% Ausgangsvariable
	\node (y) at (6,0.5) {out};
	
	% Gatter
	\node[nand port] at (1.5,0.5) (n1) {};
	\node[nand port] at (4,0.5) (n2) {};

        \draw(x1) --  (n1.in 1);
        \draw(x2) --  (n1.in 2);	
        \draw(n1.out) --  (A);
 	    \draw(A) |- (n2.in 2);
        \draw(A) |- (n2.in 1);       
        \draw(n2.out) --  (y);

\end{tikzpicture}
%!tikz source end

\end{document}