\RequirePackage{luatex85}
\documentclass{standalone}

\usepackage{fontspec}

\usepackage{tikz}
\usetikzlibrary{graphs}
\usetikzlibrary{nef}
\usetikzlibrary{quotes}

\begin{document}
\begin{tikzpicture}[nef]
    \graph {
        input [ext] -> gate [ens] -> integrator/$x$ [ens] -> output [ext];
        integrator -> [bend right, "$-1$"] gate;
        integrator -> [recurrent] integrator;
        store -> [inhibit] gate;
    };
\end{tikzpicture}
\end{document}

.
