\tikzset{block/.default={0.8cm}{0.6cm}}
\tikzset{addb/.append style={scale=0.7}}
\tikzset{node distance=0.6}
\def\cdist{0.7}

\definecolor{T}{rgb}{0.230, 0.299, 0.754}%
\definecolor{S}{rgb}{0.706, 0.016, 0.150}%
\begin{tikzpicture}
  % Blocs
  \node[block] (G) {$G$};

  \node[addb, left=of G] (addi) {};
  \node[block, above left=0.5 and 0.2 of addi] (deltai) {$\Delta_I$};
  \node[block, left=of deltai] (wi) {$w_I$};

  % Connections and labels
  \draw[->] ($(G.west)+(-4, 0)$)coordinate[](start) node[branch]{} |- (wi.west);
  \draw[->] ($(start)+(-\cdist, 0)$) -- (addi.west);
  \draw[->] (wi.east) -- (deltai.west);
  \draw[->] (deltai.east) -| (addi.north);
  \draw[->] (addi.east) -- (G.west);
  \draw[->] (G.east) -- ++(0.8, 0);

  \node[fit={(start|-wi.north) (G.south east)}, inner sep=10pt, draw, dashed, color=gray, label={$G_p$}] (Gp) {};
\end{tikzpicture}