% ---------------------------------------------------------------
% Sistema de controle em malha fechada com realimentação negativa.
% ---------------------------------------------------------------
\begin{tikzpicture}[>=Latex, line width=0.9pt, node distance=1.6cm,
  bloco/.style={draw, minimum width=2.2cm, minimum height=1.1cm, fill=blue!8},
  soma/.style={draw, circle, minimum size=0.7cm, inner sep=0pt},
  seta/.style={->}]

  \node (r) at (0,0) {$r(t)$};
  \node[soma, right=1.1cm of r]  (sum) {};
  \node[bloco, right=1.4cm of sum] (c) {$C(s)$};
  \node[bloco, right=of c]        (g) {$G(s)$};
  \node[right=1.4cm of g] (y) {$y(t)$};
  \node[bloco, below=1.3cm of c]  (h) {$H(s)$};

  \draw[seta] (r) -- (sum);
  \draw[seta] (sum) -- node[above, font=\small]{$e(t)$} (c);
  \draw[seta] (c) -- node[above, font=\small]{$u(t)$} (g);
  \draw[seta] (g) -- (y);
  \draw[seta] (g.south) |- (h.east);
  \draw[seta] (h.west) -| (sum.south);

  \node[font=\small] at ($(sum.north west)+(-0.15,0.15)$) {$+$};
  \node[font=\small] at ($(sum.south west)+(-0.15,-0.15)$) {$-$};

\end{tikzpicture}