\documentclass[tikz]{standalone}


\usetikzlibrary{arrows}
\tikzstyle{dspsquare}=[rectangle, thick, draw=black, fill=gray!10, minimum size=1cm]
\tikzstyle{dspcircle}=[circle, thick, draw=black, fill=gray!10, minimum size=1cm]
\tikzstyle{dspjoint}=[fill,draw=black,shape=circle,minimum size=3pt, inner sep=0]

\begin{document}

\begin{tikzpicture}[>=triangle 45]
\matrix(m1) [row sep=2.5mm, column sep=5mm]
{
	\node					(m00)	{$x(n)$};		        &
	\node[dspsquare]		        (m01)	{0,5};		                &
	\node[dspcircle]		        (m02)	{$+$};			        &
	\node[dspjoint]			        (m03)	{};				&
	\node					(m04)	{$y(n)$};		       \\
	%------------------------------------------------------------------------------
	\node					(m10) 	{};				&
	\node					(m11)	{};				&
	\node					(m12)	{};				&
	\node					(m23)	{};				&
	\node					(m24)	{};		               \\
	%------------------------------------------------------------------------------
	\node					(m20) 	{};				&
	\node					(m21)	{};				&
	\node[dspsquare]		        (m22)	{0,5};		                &
	\node[dspsquare]		        (m23)	{$z^{-1}$};		        &
	\node					(m24)	{};			       \\
	%------------------------------------------------------------------------------
	\node					(m30) 	{};				&
	\node					(m31)	{};				&
	\node					(m32)	{};				&
	\node					(m33)	{};				&
	\node					(m34)	{};			       \\	
	%------------------------------------------------------------------------------
};
\draw		(m33) node[below] {$y(n-1)$};
\draw[->]	(m00) -- (m01);
\draw[->]	(m01) -- (m02);
\draw[->]	(m02) -- (m04);
\draw[->]	(m03) -- (m23);
\draw[-]	(m23) |- (m32);
\draw[->]	(m33) -| (m22);
\draw[->]	(m22) -- (m02);
\end{tikzpicture}

\end{document}