Keywords
amsmath amssymb begin blox bXBloc bXInput cfrac document G_H_ H_G_ math more stalone tikz tikzpicture
\documentclass{standalone}
\usepackage{amsmath} % For math
\usepackage{amssymb} % For more math
\usepackage{blox}
\usepackage{tikz}
\begin{document}
\begin{tikzpicture}
\bXInput{A}
\bXBloc[4]{C}{$\cfrac{G_3(G_2+H_1)}{1+G_2H_2+H_3G_3(G_2+H_1)}$}{A}
\bXOutput[4]{E}{C}
\bXLink[$R(s) \quad $]{A}{C}
\bXLink[$\quad C(s)$]{C}{E}
\end{tikzpicture}
\end{document}