\documentclass[tikz]{standalone}

\usetikzlibrary{shapes.geometric, 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{dsptriangle}=[isosceles triangle, thick, draw=black, fill=gray!10, minimum size=1cm]
\tikzstyle{dspjoint}=[fill, draw=black, shape=circle, minimum size=3pt, inner sep=0]
\tikzstyle{dspio}=[draw=black, shape=circle, minimum size=5pt, inner sep=0]



\begin{document}

\begin{tikzpicture}[>=triangle 45]
\matrix(m1) [row sep=2.5mm, column sep=5mm]
{
    \node[dspio, label=left:$x(n)$]             (m00)   {};                     &
    \node[dspcircle]                            (m01)   {$+$};                  &
    \node                                       (m02)   {};                     &
    \node                                       (m03)   {};                     &
    \node[dspjoint]                             (m04)   {};                     &
    \node[dsptriangle]                          (m05)   {$b_0$};                &
    \node                                       (m06)   {};                     &
    \node[dspcircle]                            (m07)   {$+$};                  &
    \node[dspio, label=right:$y(n)$]            (m08)   {};                     \\
    %------------------------------------------------------------------------------
    \node                                       (m10)   {};                     &
    \node                                       (m11)   {};                     &
    \node                                       (m12)   {};                     &
    \node                                       (m13)   {};                     &
    \node[dspsquare]                            (m14)   {$z^{-1}$};             &
    \node                                       (m15)   {};                     &
    \node                                       (m16)   {};                     &
    \node                                       (m17)   {};                     &
    \node                                       (m18)   {};                     \\
    %------------------------------------------------------------------------------
    \node                                       (m20)   {};                     &
    \node                                       (m21)   {};                     &
    \node                                       (m22)   {};                     &
    \node[dsptriangle, shape border rotate=180] (m23)   {$a_1$};                &
    \node[dspjoint]                             (m24)   {};                     &
    \node[dsptriangle]                          (m25)   {$b_1$};                &
    \node                                       (m26)   {};                     &
    \node                                       (m27)   {};                     &
    \node                                       (m28)   {};                     \\
    %------------------------------------------------------------------------------
    \node                                       (m30)   {};                     &
    \node                                       (m31)   {};                     &
    \node                                       (m32)   {};                     &
    \node                                       (m33)   {};                     &
    \node                                       (m34)   {};                     &
    \node                                       (m35)   {};                     &
    \node                                       (m36)   {};                     &
    \node                                       (m37)   {};                     &
    \node                                       (m38)   {};                     \\
    %------------------------------------------------------------------------------
    \node                                       (m40)   {};                     &
    \node                                       (m41)   {};                     &
    \node                                       (m42)   {};                     &
    \node                                       (m43)   {};                     &
    \node                                       (m44)   {};                     &
    \node                                       (m45)   {};                     &
    \node                                       (m46)   {};                     &
    \node                                       (m47)   {};                     &
    \node                                       (m48)   {};                     \\
    %------------------------------------------------------------------------------
    \node                                       (m50)   {};                     &
    \node                                       (m51)   {};                     &
    \node                                       (m52)   {};                     &
    \node                                       (m53)   {};                     &
    \node[dspsquare]                            (m54)   {$z^{-1}$};             &
    \node                                       (m55)   {};                     &
    \node                                       (m56)   {};                     &
    \node                                       (m57)   {};                     &
    \node                                       (m58)   {};                     \\
    %------------------------------------------------------------------------------
    \node                                       (m60)   {};                     &
    \node                                       (m61)   {};                     &
    \node                                       (m62)   {};                     &
    \node[dsptriangle, shape border rotate=180] (m63)   {$a_N$};                &
    \node[dspjoint]                             (m64)   {};                     &
    \node[dsptriangle]                          (m65)   {$b_N$};                &
    \node                                       (m66)   {};                     &
    \node                                       (m67)   {};                     &
    \node                                       (m68)   {};                     \\
    %------------------------------------------------------------------------------
};

\draw[->]   (m00) -- (m01);
\draw[->]   (m01) -- (m05);
\draw[->]   (m04) -- (m14);
\draw[->]   (m05) -- (m07);
\draw[-]    (m07) -- (m08);

\draw[->]   (m23) -- (m22.west) -- (m01);
\draw[->]   (m24) -- (m23);
\draw[->]   (m24) -- (m25);
\draw[->]   (m25) -- (m26.east) -- (m07);
\draw[-]    (m14) -- (m24);

\draw[->, densely dashed]   (m24) -- (m54);

\draw[->]   (m63) -- (m62.west) -- (m01);
\draw[->]   (m64) -- (m63);
\draw[->]   (m64) -- (m65);
\draw[->]   (m65) -- (m66.east) -- (m07);
\draw[-]    (m54) -- (m64);
\end{tikzpicture}

\end{document}