Hypothetical uniform quantizer standalone class figure.
\begin
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%Created by Lucas dos Santos Costa (July/2019)
\documentclass{standalone}
\usepackage{amsmath}
\usepackage{tikz,pgfplots}\pgfplotsset{compat=newest}
\usetikzlibrary{shapes,arrows}
\usetikzlibrary{calc,patterns,decorations.pathmorphing,decorations.markings}
\usetikzlibrary{shadows}
\begin{document}
\begin{tikzpicture}[yscale=1,>=latex']
\draw[<->](-5,0)--(5,0) node [pos=0.99,below] {\ensuremath{y}};
\draw [black,samples=200,domain=-4.8:4.8,dashed,line width=0.25mm] plot (\x, {1.5*exp(-(\x+0)^2/2.6)}); \node at (0,1.65) {{\scriptsize Input signal distribution}};
%
\draw[<->](-5,0.5)--(-3.4,0.5) node[midway,fill=white] {$r_1$};
\draw[-](-4.2,-0.25)--(-4.2,0); \node at (-4.2,-0.6) {$n_1$};
\draw[-](-3.4,-0.5)--(-3.4,0.75); \node at (-3.4,1) {$z_1$};
\draw[<->](-3.4,0.5)--(-1.65,0.5) node[midway,fill=white] {$r_2$};
\draw[-](-2.525,-0.25)--(-2.525,0); \node at (-2.525,-0.6) {$n_2$};
\draw[-](-1.65,-0.5)--(-1.65,0.75); \node[xshift = -0.5mm, yshift = -1mm] at (-1.65,1) {$z_2$};
%
\node at (-1.45,0.5) {...};
%
\draw[-](-1.25,-0.5)--(-1.25,0.75); \node[xshift = 0.5mm, fill = white, anchor = base, inner sep = 0.7pt] at (-1.25,1) {$z_{u-1}$};
\draw[<->](-1.25,0.5)--(-0,0.5) node[midway,fill=white] {$r_{u}$};
\draw[-](-0.625,-0.25)--(-0.625,0); \node[yshift = +1mm] at (-0.625,-0.6) {$n_{u-1}$};
\draw[-](0,-0.5)--(0,0.75); \node[fill=white] at (0,1) {$z_{u}$};
\draw[<->](0,0.5)--(1.25,0.5) node[midway,fill=white] {$r_{u+1}$};
\draw[-](0.625,-0.25)--(0.625,0); \node at (0.625,-0.6) {$n_{u+1}$};
\draw[-](1.25,-0.5)--(1.25,0.75); \node[xshift = -1mm, yshift = -1mm, fill = white, anchor = base, inner sep = 0.7pt] at (1.25,1) {$z_{u+1}$};
%
\node at (1.45,0.5) {...};
%
\draw[-](1.65,-0.5)--(1.65,0.75); \node[xshift = +1mm, yshift = +1mm] at (1.65,1) {$z_{N_\text{Q}-2}$};
\draw[<->](1.65,0.5)--(3.15,0.5) node[midway,fill = white, anchor = base, inner sep = 0.7pt] {$r_{N_\text{Q}-1}$};
\draw[-](2.4,-0.25)--(2.4,0); \node at (2.4,-0.6) {$n_{N_\text{Q}-1}$};
\draw[-](3.15,-0.5)--(3.15,0.75); \node at (3.15,1) {$z_{N_\text{Q}-1}$};
\draw[<->](3.15,0.5)--(5,0.5) node[midway, fill = white] {$r_{N_\text{Q}}$};
\draw[-](3.9,-0.25)--(3.9,0); \node at (3.9,-0.6) {$n_{N_\text{Q}}$};
\end{tikzpicture}
\end{document}