\documentclass[11pt, a4paper]{article}
\usepackage[a4paper,left=20mm,right=20mm,top=25mm,bottom=25mm]{geometry}

\usepackage{svg}

% TikZ
\usepackage{tikz}
\usetikzlibrary{shapes, arrows, shadows, arrows.meta}
\usetikzlibrary{fit}

\usepackage{calc}

% Conditionals in TikZ
\usepackage{ifthen}

% Lists
\usepackage{enumitem}

% Math
\usepackage{amsmath, bm}
\usepackage{mathrsfs}
\usepackage{textcomp} % Get rid of gensymb warnings
\usepackage{gensymb} % For the degree symbol
\usepackage{siunitx} % SI Units

% Color
\usepackage{xcolor}
\definecolor{light_blue}{RGB}{222,235,247}

\begin{document}
    %===================================================================================
    % TIKZ PX4 CONTROLLERS
    %===================================================================================

    \begin{figure}[h]
      \centering

      % Define distances
      \def\blockheight{7em}
      \def\largeblockheight{1.45*\blockheight}
      \def\blockwidth{3.9em}
      \def\nodesep{1.15*\blockwidth}

      \footnotesize
      \begin{tikzpicture}[>={Stealth[inset=0pt,length=3pt,angle'=60,round]},
          simple_block/.style = {draw, fill=light_blue, text centered, inner sep=0pt, text width=\blockwidth, minimum height=\blockheight},
          larger_block/.style = {draw, fill=light_blue, text centered, inner sep=0pt, text width=\blockwidth, minimum height=\largeblockheight, anchor=north},
          no_border_block/.style = {text centered, inner ysep=0.5em},
          frame_block/.style = {draw, text centered, inner ysep=2.25em, inner xsep=0.5em, dashed}
      ]
        \hspace{-1.05cm}
        %===================================================================================

        % Reference
        \node (ref) [] {};

        % Position controller
        \path (ref.east)+(0.85*\nodesep,0) node (pos_ctrl) [simple_block] {Position Control};
        \path (pos_ctrl.north)+(0,0) node (pos_ctrl_text) [no_border_block, anchor=south] {\textbf{P}};
        \path (pos_ctrl.south)+(0.65*\nodesep, -0.075*\blockheight) node (pos_ctrl_freq_text) [no_border_block, anchor=north] {50 Hz};

        % Velocity controller
        \path (pos_ctrl.east)+(0.85*\nodesep,0) node (vel_ctrl) [simple_block] {Velocity Control};
        \path (vel_ctrl.north)+(0,0) node (vel_ctrl_text) [no_border_block, anchor=south] {\textbf{PID}};

        % Acceleration to Attitude
        \path (vel_ctrl.north east)+(1.1*\nodesep,0) node (force_2_att) [larger_block, text width=5.6em] {Acceleration and Yaw to Attitude};

        % Inertial Frame
        \node[fit=(pos_ctrl) (vel_ctrl)] (inertial) [frame_block] {};
        \path (inertial.south)+(0,0) node (inertial_text) [no_border_block, anchor=north] {Inertial Frame};

        % Angle controller
        \path (force_2_att.north east)+(0.95*\nodesep,0) node (angle_ctrl) [simple_block, anchor=north] {Angle Control};
        \path (angle_ctrl.north)+(0,0) node (angle_ctrl_text) [no_border_block, anchor=south] {\textbf{P}};
        \path (angle_ctrl.south)+(0, -0.075*\blockheight) node (angle_ctrl_freq_text) [no_border_block, anchor=north] {250 Hz};

        % Angular Rate controller
        \path (angle_ctrl.east)+(0.9*\nodesep,0) node (ang_vel_ctrl) [simple_block] {Angular Rate Control};
        \path (ang_vel_ctrl.north)+(0,0) node (ang_vel_ctrl_text) [no_border_block, anchor=south] {\textbf{PID}};
        \path (ang_vel_ctrl.south)+(0, -0.075*\blockheight) node (ang_vel_ctrl_freq_text) [no_border_block, anchor=north] {1 kHz};

        % Mixer
        \path (ang_vel_ctrl.north east)+(\nodesep,0) node (mixer) [larger_block, text width=3em] {Mixer};

        % Body Frame
        \node[fit=(angle_ctrl) (ang_vel_ctrl)] (body) [frame_block] {};
        \path (body.south)+(0,0) node (body_text) [no_border_block, anchor=north] {Body Frame};

        \path (mixer.east)+(0.5*\nodesep,0) node (cmd) [] {};

        %===================================================================================

        \path[draw,->] (ref.east) -- node[anchor=south, pos=0.05, align=left] {$\bm{X}_\text{sp}$} (pos_ctrl.west);

        \path[draw,->] (pos_ctrl.east) -- node[anchor=south] {$\bm{V}_\text{sp}$} (vel_ctrl.west);

        \path[draw,->] (vel_ctrl.east) -- node[anchor=south, pos=0.65] {$\bm{A}_\text{sp}$} (vel_ctrl.east -| force_2_att.west);
        \path[draw,->] ([yshift=-0.25*\largeblockheight]force_2_att.west -| ref.east) -- node[anchor=south, pos=0] {$\psi_\text{sp}$} ([yshift=-0.25*\largeblockheight]force_2_att.west);

        \path[draw,->] (force_2_att.east |- angle_ctrl.west) -- node[anchor=south, pos=0.4] {$\bm{q}_\text{sp}$} (angle_ctrl.west);
        \path[draw,->] ([yshift=-0.25*\largeblockheight]force_2_att.east) -- node[text centered, inner sep=2pt, anchor=south, pos=0.915] {$\delta_{T_\text{sp}}$} ([yshift=-0.25*\largeblockheight]mixer.west);

        \path[draw,->] (angle_ctrl.east) -- node[anchor=south] {$\bm{\Omega}_\text{sp}$} (ang_vel_ctrl.west);

        \path[draw,->] ([yshift=0.25*\blockheight]ang_vel_ctrl.east) -- node[text centered, inner sep=2pt, anchor=south, pos=0.6] {$\delta_{A_\text{sp}}$} ([yshift=0.25*\blockheight]ang_vel_ctrl.east -| mixer.west);
        \path[draw,->] (ang_vel_ctrl.east) -- node[text centered, inner sep=2pt, anchor=south, pos=0.6] {$\delta_{E_\text{sp}}$} (ang_vel_ctrl.east -| mixer.west);
        \path[draw,->] ([yshift=-0.25*\blockheight]ang_vel_ctrl.east) -- node[text centered, inner sep=2pt, anchor=south, pos=0.6] {$\delta_{R_\text{sp}}$} ([yshift=-0.25*\blockheight]ang_vel_ctrl.east -| mixer.west);

        \path[draw,->] (mixer.east) -- node[text centered, inner sep=5pt, anchor=south] {$\bm{T}_\text{sp}$} (cmd.west);

      \end{tikzpicture}
    \end{figure}

    \clearpage

    %===================================================================================
    % TIKZ ANGULAR RATE CONTROL
    %===================================================================================

    \begin{figure}[ht]
      \centering

      % Define distances
      \def\blockheight{2.2em}
      \def\blockwidth{2.2em}
      \def\nodesep{1.5*\blockwidth}

      \begin{tikzpicture}[>={Stealth[inset=0pt,length=3pt,angle'=60,round]},
        simple_block/.style = {draw, fill=light_blue, text centered, inner sep=0pt, minimum width=\blockwidth, minimum height=\blockheight},
        frame_block/.style = {draw, text centered, inner ysep=1.25em, inner xsep=1.25em, dashed},
        port/.style = {inner sep=0pt, font=\tiny},
        sum/.style n args = {4}{draw, circle, minimum size=1.5em, alias=sum,
          append after command = {
            node at (sum.north) [port, below=1pt] {$#1$}
            node at (sum.west) [port, right=1pt] {$#2$}
            node at (sum.south) [port, above=1pt] {$#3$}
            node at (sum.east) [port, left=1pt] {$#4$}
          }
        },
        sat_block/.style = {draw, minimum width=\blockwidth, minimum height=\blockheight, path picture =
          {
          % Get the width and height of the path picture node
          \pgfpointdiff{\pgfpointanchor{path picture bounding box}{north east}}%
              {\pgfpointanchor{path picture bounding box}{south west}}
          \pgfgetlastxy\x\y
          % Scale the x and y vectors so that the range
          % -1 to 1 is slightly shorter than the size of the node
          \tikzset{x=\x*.4, y=\y*.4}
          %
          % Draw annotation
          \draw (-1,0) -- (1,0) (0,-1) -- (0,1);
          \draw (-1,-.6) -- (-.6,-.6) -- (.6,.6) -- (1,.6);
          }
        },
        sat_block_int/.style = {draw, minimum width=\blockwidth, minimum height=\blockheight, path picture =
          {
          % Get the width and height of the path picture node
          \pgfpointdiff{\pgfpointanchor{path picture bounding box}{north east}}%
              {\pgfpointanchor{path picture bounding box}{south west}}
          \pgfgetlastxy\x\y
          % Scale the x and y vectors so that the range
          % -1 to 1 is slightly shorter than the size of the node
          \tikzset{x=\x*.4, y=\y*.4}
          %
          % Draw annotation
          \draw (-.8,-.9) -- (-.6,-.9) -- (.1,.5) -- (.3,.5);
          }
        }
      ]
        %===================================================================================
        \node[text centered] (ref) {};

        % Controller
        \path(ref)+(\nodesep,0) node (ref_sum) [sum={}{+}{-}{}] {};
        \path(ref_sum)+(\nodesep,0) node (ctrl_k) [simple_block] {$K$};
        \path(ctrl_k)+(2*\nodesep,0) node (ctrl_i) [sat_block_int, fill=light_blue, text centered, inner sep=0pt] {$~~\int$};
        \path(ctrl_i)+(\nodesep,0) node (ctrl_i_gain) [simple_block] {$I$};
        \path(ref_sum)+(\nodesep,-1.5*\blockheight) node (ctrl_kd) [simple_block] {$K$};
        \path(ctrl_kd)+(\nodesep,0) node (ctrl_d_filt) [simple_block] {LPF};
        \path(ref_sum)+(3*\nodesep,-1.5*\blockheight) node (ctrl_d) [simple_block] {$\frac{\partial}{\partial t}$};
        \path(ctrl_d)+(\nodesep,0) node (ctrl_d_gain) [simple_block] {$D$};
        \path(ref_sum)+(4*\nodesep,1.5*\blockheight) node (ctrl_p_gain) [simple_block] {$P$};
        \path(ctrl_i_gain)+(\nodesep,0) node (ctrl_sum) [sum={+}{+}{-}{}] {};
        \path(ctrl_sum)+(\nodesep,0) node (sat_ctrl) [sat_block] {};
        \path(sat_ctrl.east)+(0.675*\nodesep,0) node (ctrl) [] {};

        \path(ref_sum.south |- ctrl_d_filt.west)+(-\nodesep,0) node(output) [] {};

        %===================================================================================
        \path[draw,->] (ref.east) -- node[anchor=south, pos=0] {$\Omega_\text{sp}$} (ref_sum.west);

        \path[draw,->] (ref_sum.east) -- (ctrl_k.west);
        \path[draw,->] (ctrl_k.east) -- (ctrl_i.west);
        \path[draw,->] (output.east) |- node[anchor=south, pos=0] {$\Omega$} (ctrl_kd.west);
        \path[draw,->] (ctrl_kd.east) -- (ctrl_d_filt.west);
        \path[draw,->] (output.east -| ref_sum.south) -- (ref_sum.south);
        \path[draw,->] ([xshift=0.65*\nodesep]ctrl_k.east) |- (ctrl_p_gain.west);
        \path[draw,->] (ctrl_i.east) -- (ctrl_i_gain.west);
        \path[draw,->] (ctrl_d_filt.east) -- (ctrl_d.west);
        \path[draw,->] (ctrl_d.east) -- (ctrl_d_gain.west);
        \path[draw,->] (ctrl_d_gain.east) -| (ctrl_sum.south);
        \path[draw,->] (ctrl_i_gain.east) -- (ctrl_sum.west);
        \path[draw,->] (ctrl_p_gain.east) -| (ctrl_sum.north);
        \path[draw,->] (ctrl_sum.east) -- (sat_ctrl.west);
        \path[draw,->] (sat_ctrl.east) -- node[anchor=south] {$\delta_\text{sp}$} (ctrl.west);

      \end{tikzpicture}

    \end{figure}

    \clearpage

    %===================================================================================
    % TIKZ ANGLE CONTROL
    %===================================================================================

    \begin{figure}[ht]
      \centering
      \footnotesize

      % Define distances
      \def\blockheight{3em}
      \def\blockwidth{3em}
      \def\nodesep{2*\blockwidth}

      \begin{tikzpicture}[>={Stealth[inset=0pt,length=3pt,angle'=60,round]},
        simple_block/.style = {draw, fill=light_blue, text centered, inner sep=0pt, minimum width=\blockwidth, minimum height=\blockheight},
        text_block/.style = {draw, fill=light_blue, text centered, inner sep=0pt, text width=2*\blockwidth, minimum height=\blockheight},
        frame_block/.style = {draw, text centered, inner ysep=1.25em, inner xsep=1.25em, dashed},
        sat_block/.style = {draw, minimum width=\blockwidth, minimum height=\blockheight, path picture =
            {
            % Get the width and height of the path picture node
            \pgfpointdiff{\pgfpointanchor{path picture bounding box}{north east}}%
                {\pgfpointanchor{path picture bounding box}{south west}}
            \pgfgetlastxy\x\y
            % Scale the x and y vectors so that the range
            % -1 to 1 is slightly shorter than the size of the node
            \tikzset{x=\x*.4, y=\y*.4}
            %
            % Draw annotation
            \draw (-1,0) -- (1,0) (0,-1) -- (0,1);
            \draw (-1,-.6) -- (-.6,-.6) -- (.6,.6) -- (1,.6);
            }
        },
        gain/.style = {draw, fill=light_blue, inner sep=0pt, isosceles triangle, minimum height=\blockheight, isosceles triangle apex angle=60},
      ]
        \hspace{-0.7cm}

        %===============================================================================
        \node[text centered] (ref) {};

        % Reference model: 2nd-order critically-damped model (natural frequency MC_REF_W_N)
        % that smooths the setpoint q_sp into the reference attitude q_ref tracked by the
        % P law, and outputs the reference body rate omega_ref used as feedforward.
        \path(ref)+(0.9*\nodesep,0) node (ref_model) [text_block] {Reference model};

        % Controller
        \path(ref_model)+(1.5*\nodesep,0) node (err_quat) [text_block] {Error quaternion};
        \path(err_quat)+(1.5*\nodesep,0) node (select_axis) [text_block] {Extract component};
        \path(select_axis)+(0, 1.5*\blockheight) node (select_mag) [text_block] {Extract magnitude};
        \path(select_mag)+(1.1*\nodesep,0) node (sgn) [simple_block] {sgn};
        \path(select_axis)+(1.9*\nodesep, 0.25*\blockheight) node (mult) [simple_block] {$\times$};
        \path(mult)+(0.65*\nodesep, 0) node (p_gain) [gain] {\scriptsize $2 P$};
        % Summing junction: P-law rate + reference-model rate feedforward, BEFORE the final rate saturation
        \path(p_gain)+(0.7*\nodesep, 0) node (sum) [draw, circle, inner sep=1.5pt] {$+$};
        \path(sum)+(0.7*\nodesep, 0) node (sat_ctrl) [sat_block] {};
        \path(sat_ctrl)+(0.7*\nodesep, 0) node (output) [] {};
        % omega_ref feedforward chain: gain (MC_REF_FF) then per-axis saturation (MC_REF_FF_MAX)
        \path(sum)+(-0.7*\nodesep, -2.7*\blockheight) node (ff_sat) [sat_block] {};
        \path(ff_sat)+(-1.1*\nodesep, 0) node (ff_gain) [gain] {\scriptsize $k_\text{ff}$};

        %===============================================================================
        \path[draw,->] (ref.east) -- node[text centered, anchor=south, pos=0.3] {$\bm{q}_\text{sp}$} (ref_model.west);
        \path[draw,->] (ref_model.east) -- node[text centered, anchor=south] {$\bm{q}_\text{ref}$} (err_quat.west);
        \path[draw,->] ([yshift=-0.75*\blockheight]err_quat.south) -- node[text centered, anchor=east, pos=0] {$\bm{q}$} (err_quat.south);
        \path[draw,->] (err_quat.east) -- node[text centered, anchor=south,pos=0.4] {$\bm{q}_\text{e}$} (select_axis.west);
        \path[draw,->]([xshift=0.3*\nodesep]err_quat.east) |- (select_mag.west);
        \path[draw,->] (select_mag.east) -- node[text centered, anchor=south] {$q_{0_\text{e}}$} (sgn.west);
        \path[draw,->] (sgn.east) -- ([xshift=0.15*\nodesep]sgn.east) |- ([yshift=0.25*\blockheight]mult.west);
        \path[draw,->] (select_axis.east) -- node[text centered, anchor=south, pos=0.45]{$q_{j_\text{e}}$} ([yshift=-0.25*\blockheight]mult.west);
        \path[draw,->] (mult.east) -- (p_gain.west);
        \path[draw,->] (p_gain.east) -- (sum.west);
        \path[draw,->] (sum.east) -- (sat_ctrl.west);
        \path[draw,->] (sat_ctrl.east) -- node[text centered, anchor=south] {$\Omega_\text{sp}$} (output.west);
        % omega_ref feedforward: reference model -> gain -> saturation -> summing junction
        \path[draw,->] (ref_model.south) |- (ff_gain.west);
        \node[text centered, anchor=south] at (select_axis |- ff_gain) {$\bm{\omega}_\text{ref}$};
        \path[draw,->] (ff_gain.east) -- (ff_sat.west);
        \path[draw,->] (ff_sat.east) -| (sum.south);
      \end{tikzpicture}

    \end{figure}

    \clearpage

    %===================================================================================
    % TIKZ VELOCITY CONTROL
    %===================================================================================

    \begin{figure}[ht]
      \centering

      % Define distances
      \def\blockheight{2.2em}
      \def\blockwidth{2.2em}
      \def\nodesep{1.5*\blockwidth}

      \begin{tikzpicture}[>={Stealth[inset=0pt,length=3pt,angle'=60,round]},
        simple_block/.style = {draw, fill=light_blue, text centered, inner sep=0pt, minimum width=\blockwidth, minimum height=\blockheight},
        frame_block/.style = {draw, text centered, inner ysep=1.25em, inner xsep=1.25em, dashed},
        port/.style = {inner sep=0pt, font=\tiny},
        sum/.style n args = {4}{draw, circle, minimum size=1.5em, alias=sum,
          append after command = {
            node at (sum.north) [port, below=1pt] {$#1$}
            node at (sum.west) [port, right=1pt] {$#2$}
            node at (sum.south) [port, above=1pt] {$#3$}
            node at (sum.east) [port, left=1pt] {$#4$}
          }
        },
        sat_block/.style = {draw, minimum width=\blockwidth, minimum height=\blockheight, path picture =
          {
          % Get the width and height of the path picture node
          \pgfpointdiff{\pgfpointanchor{path picture bounding box}{north east}}%
              {\pgfpointanchor{path picture bounding box}{south west}}
          \pgfgetlastxy\x\y
          % Scale the x and y vectors so that the range
          % -1 to 1 is slightly shorter than the size of the node
          \tikzset{x=\x*.4, y=\y*.4}
          %
          % Draw annotation
          \draw (-1,0) -- (1,0) (0,-1) -- (0,1);
          \draw (-1,-.6) -- (-.6,-.6) -- (.6,.6) -- (1,.6);
          }
        },
        sat_block_int/.style = {draw, minimum width=\blockwidth, minimum height=\blockheight, path picture =
          {
          % Get the width and height of the path picture node
          \pgfpointdiff{\pgfpointanchor{path picture bounding box}{north east}}%
              {\pgfpointanchor{path picture bounding box}{south west}}
          \pgfgetlastxy\x\y
          % Scale the x and y vectors so that the range
          % -1 to 1 is slightly shorter than the size of the node
          \tikzset{x=\x*.4, y=\y*.4}
          %
          % Draw annotation
          \draw (-.8,-.9) -- (-.6,-.9) -- (.1,.5) -- (.3,.5);
          }
        }
      ]
        %===================================================================================
        \node[text centered] (ref) {};

        % Controller
        \path(ref)+(\nodesep,0) node (ref_sum) [sum={}{+}{-}{}] {};
        \path(ref_sum)+(2*\nodesep,0) node (ctrl_i) [simple_block] {$\int$};
        \path(ctrl_i)+(\nodesep,0) node (ctrl_i_gain) [simple_block] {$I$};
        \path(ref_sum)+(\nodesep,-1.5*\blockheight) node (ctrl_d_filt) [simple_block] {LPF};
        \path(ref_sum)+(2*\nodesep,-1.5*\blockheight) node (ctrl_d) [simple_block] {$\frac{\partial}{\partial t}$};
        \path(ctrl_d)+(\nodesep,0) node (ctrl_d_gain) [simple_block] {$D$};
        \path(ref_sum)+(3*\nodesep,1.5*\blockheight) node (ctrl_p_gain) [simple_block] {$P$};
        \path(ctrl_i_gain)+(\nodesep,0) node (ctrl_sum) [sum={+}{+}{-}{}] {};
        \path(ctrl_sum)+(\nodesep,0) node (sat_ctrl) [sat_block] {};
        \path(sat_ctrl.east)+(0.675*\nodesep,0) node (ctrl) [] {};

        \path(ref_sum.south |- ctrl_d_filt.west)+(-\nodesep,0) node(output) [] {};

        %===================================================================================
        \path[draw,->] (ref.east) -- node[anchor=south, pos=0] {$V_\text{sp}$} (ref_sum.west);

        \path[draw,->] (ref_sum.east) -- (ctrl_i.west);
        \path[draw,->] (output.east) |- node[anchor=south, pos=0] {$V$} (ctrl_d_filt.west);
        \path[draw,->] (output.east -| ref_sum.south) -- (ref_sum.south);
        \path[draw,->] ([xshift=0.65*\nodesep]ref_sum.east) |- (ctrl_p_gain.west);
        \path[draw,->] (ctrl_i.east) -- (ctrl_i_gain.west);
        \path[draw,->] (ctrl_d_filt.east) -- (ctrl_d.west);
        \path[draw,->] (ctrl_d.east) -- (ctrl_d_gain.west);
        \path[draw,->] (ctrl_d_gain.east) -| (ctrl_sum.south);
        \path[draw,->] (ctrl_i_gain.east) -- (ctrl_sum.west);
        \path[draw,->] (ctrl_p_gain.east) -| (ctrl_sum.north);
        \path[draw,->] (ctrl_sum.east) -- (sat_ctrl.west);
        \path[draw,->] (sat_ctrl.east) -- node[anchor=south] {$A_\text{sp}$} (ctrl.west);

      \end{tikzpicture}

    \end{figure}

    \clearpage

    %===================================================================================
    % TIKZ POSITION CONTROL
    %===================================================================================

    \begin{figure}[h]
      \centering

      % Define distances
      \def\blockheight{2.2em}
      \def\blockwidth{2.2em}
      \def\nodesep{2*\blockwidth}

      \begin{tikzpicture}[>={Stealth[inset=0pt,length=3pt,angle'=60,round]},
        simple_block/.style = {draw, fill=light_blue, text centered, inner sep=0pt, minimum width=\blockwidth, minimum height=\blockheight},
        frame_block/.style = {draw, text centered, inner ysep=1.25em, inner xsep=1.25em, dashed},
        port/.style = {inner sep=0pt, font=\tiny},
        sum/.style n args = {4}{draw, circle, minimum size=1.5em, alias=sum,
          append after command = {
            node at (sum.north) [port, below=1pt] {$#1$}
            node at (sum.west) [port, right=1pt] {$#2$}
            node at (sum.south) [port, above=1pt] {$#3$}
            node at (sum.east) [port, left=1pt] {$#4$}
          }
        },
        sat_block/.style = {draw, minimum width=\blockwidth, minimum height=\blockheight, path picture =
          {
          % Get the width and height of the path picture node
          \pgfpointdiff{\pgfpointanchor{path picture bounding box}{north east}}%
              {\pgfpointanchor{path picture bounding box}{south west}}
          \pgfgetlastxy\x\y
          % Scale the x and y vectors so that the range
          % -1 to 1 is slightly shorter than the size of the node
          \tikzset{x=\x*.4, y=\y*.4}
          %
          % Draw annotation
          \draw (-1,0) -- (1,0) (0,-1) -- (0,1);
          \draw (-1,-.6) -- (-.6,-.6) -- (.6,.6) -- (1,.6);
          }
        }
      ]
        %===============================================================================
        \node[text centered] (ref) {};

        % Controller
        \path(ref)+(\nodesep,0) node (ref_sum) [sum={}{+}{-}{}] {};
        \path(ref_sum)+(\nodesep,0) node (ctrl_p_gain) [simple_block] {$P$};
        \path(ctrl_p_gain)+(\nodesep,0) node (sat_ctrl) [sat_block] {};
        \path(sat_ctrl.east)+(\nodesep,0) node (ctrl) [] {};

        \path(ref_sum.south)+(-\nodesep,-1.5*\blockheight) node(output) [] {};

        %===============================================================================
        \path[draw,->] (ref.east) -- node[anchor=south, pos=0] {$X_\text{sp}$} (ref_sum.west);

        \path[draw,->] (output.east) -- node[anchor=south, pos=0] {$X$} (output.east -| ref_sum.south) -- (ref_sum.south);
        \path[draw,->] (ref_sum.east) -- (ctrl_p_gain.west);
        \path[draw,->] (ctrl_p_gain.east) -- (sat_ctrl.west);
        \path[draw,->] (sat_ctrl.east) -- node[anchor=south] {$V_\text{sp}$} (ctrl.west);

      \end{tikzpicture}

    \end{figure}

\end{document}