% ---------------------------------------------------------------
% Álgebra de blocos: associação em série (cascata).
% ---------------------------------------------------------------
\begin{tikzpicture}[>=Latex, line width=0.9pt, node distance=1.3cm,
  bloco/.style={draw, minimum width=1.8cm, minimum height=1.0cm, fill=blue!8},
  seta/.style={->}]

  \node (x) at (0,0) {$X(s)$};
  \node[bloco, right=of x] (g1) {$G_1(s)$};
  \node[bloco, right=of g1] (g2) {$G_2(s)$};
  \node[right=of g2] (y) {$Y(s)$};
  \draw[seta] (x) -- (g1);
  \draw[seta] (g1) -- (g2);
  \draw[seta] (g2) -- (y);

  \node[font=\Large, right=1.1cm of y] (eq) {$\equiv$};

  \node[right=1.1cm of eq] (x2) {$X(s)$};
  \node[bloco, right=of x2, minimum width=2.6cm] (geq) {$G_1(s)\,G_2(s)$};
  \node[right=of geq] (y2) {$Y(s)$};
  \draw[seta] (x2) -- (geq);
  \draw[seta] (geq) -- (y2);

\end{tikzpicture}