Draw block diagram using Tikz package

Question

Please how can I draw the figure shown below in Latex? I copied the figure from a journal. I am currently using Tikz package. Thank you for your help.

Update:

My code is shown below.

\begin{tikzpicture}
 
% Zero order block 
\node[draw,
    minimum width=2cm,
    minimum height=1.2cm,
] (ZOH) at (0,0){$Hold (H)$};

% High altitude balloon block
\node [draw, 
    minimum width=2cm, 
    minimum height=1.2cm, 
    above right= 0.5cm and 1cm of ZOH
]  (plant) {Plant (G) $\dot{x} = f(x(t), u(t), w(t))$};

% Sampler
\node [draw, 
    minimum width=2cm, 
    minimum height=1.2cm, 
    below right= 0.5cm and 1cm of plant
]  (sampler) {Sampler $[k]$};

% Extremum seeking controller
\node [draw, 
    minimum width=2cm, 
    minimum height=1.2cm, 
    below right= 0.5cm and 1cm of ZOH] 
     (ESC) {Controller (K) ;
          $\hat{u}_j = K(\hat{x}_j)$ };

% Arrows with text label
\draw[-stealth] (ZOH.north) |- (plant.west)
    node[near end,above]{$u(t)$};

\draw[-stealth] (plant.east) -| (sampler.north)
    node[near start,above]{$x(t)$}; 

\draw[-stealth] (sampler.south) |- (ESC.east)
    node[near end,below]{$J[k]$};   

\draw[-stealth] (ESC.west) -| (ZOH.south)
    node[near start,below]{$\hat{u}_j$};        

\end{tikzpicture}

Answer 1

Hope this helps:

\documentclass{article}
\usepackage[utf8]{inputenc}
\usepackage{tikz}
\usetikzlibrary{positioning,arrows.meta}

\begin{document}

\begin{tikzpicture}[>=stealth]
 
% Zero order block 
\node[draw=black!50,ultra thick,
minimum width=2.2cm,
minimum height=1cm,fill=cyan!30] (ZOH) at (0,0){Hold $(H)$};

% High altitude balloon block
\node [draw=black!50, 
    minimum width=2cm, 
    minimum height=1.5cm, 
    above right= 0.5cm and 1cm of ZOH,
    align=center, ultra thick,fill=cyan!30
]  (plant) {Plant (G)\\$\dot{x}(t) = f(x(t), u(t), w(t))$};

% Sampler
\node [draw=black!50, 
    minimum width=2cm, 
    minimum height=1.2cm, 
    below right= 0.5cm and 1cm of plant, ultra thick,fill=cyan!30,
    align=center
]  (sampler) {Sampler $(S)$\\sampling instants, $\{r_j\}$};

% Extremum seeking controller
\node [draw=black!50, 
    minimum width=3cm, 
    minimum height=1.5cm, ultra thick, fill=cyan!30,
    below right= 0.5cm and 1.6cm of ZOH,
    align=center] 
     (ESC) {Controller (K)\\
    $\hat{u}_j = K(\hat{x}_j)$ };

% Arrows with text label
\draw[->,ultra thick] (ZOH.north) |- (1.9,1.7);
\draw (-0.5,1.7) node {$u(t)$};

\draw[->,ultra thick] (plant.east) -| (sampler.north)
    node[near start,above]{$x(t)$}; 

\draw[->,ultra thick] (sampler.south) |- (ESC.east)
    node[near end,below right]{$\hat{x}_j=x(r_j)$};   

\draw[->,ultra thick] (ESC.west) -| (ZOH.south)
    node[near end,left]{$\hat{u}_j$};   
\draw[->, ultra thick] (0,2.2) node[anchor=east] {$w(t)$} -- (1.9,2.2);

\end{tikzpicture}

\end{document}

The key for the linebreaks in the node text was to use align=center. Then I just changed the thickness of the lines and arrows, and moved some of the nodes around, changed the colors, and then of course, added the extra arrow near the top left.