feedback1d
\documentclass{standalone} \usepackage{tikz} \usetikzlibrary{shapes,positioning} \usetikzlibrary{narrow} \tikzset{block/.style={draw, rectangle, line width=2pt, minimum height=3em, minimum width=3em, outer sep=0pt}} \tikzset{sumcircle/.style={draw, circle, outer sep=0pt, label=center:{{$\sum$}}, minimum width=2em}} \tikzset{every picture/.style={auto, line width=1pt, >=narrow,font=\small}} \begin{document} \begin{tikzpicture} \node[block](G1){$G_1$}; \node[block,above=7 mm of G1](G4){$G_4$}; \node[sumcircle,right=10mm of G1](sum2){}; \node[block,right=10mm of sum2](G2){$G_2$}; \node[block,below=9mm of sum2](G3){$G_3$}; \node[sumcircle,left=12mm of G1](sum){}; \node[coordinate, left=15mm of sum](ref){}; \node[coordinate, left=6mm of sum](fork){}; \draw[->](ref)--node[xshift=-4mm](){$R$}(sum); \draw[->](sum)--node[xshift=-1mm](){$E$}(G1); \draw[->](G1)--(sum2); \draw[->](sum2)--(G2); \draw[->](fork)|-(G4); \draw[->](G4)-|(sum2); \node[coordinate, right=12mm of G2](output){}; \draw[->](G2)--node[xshift=0mm](Y){$Y$}(output); \draw[->](Y)|-(G3); \draw[->](G3)-|(sum); \end{tikzpicture} \end{document}