Minimize size of a figure (tikz - pgf) in LaTeX

Question

I'm using MikTeX and WinEdt for writing an IEEE conference paper. To create a neural network structure I used this code :

\begin{figure}
\begin{tikzpicture}[
init/.style={
  draw,
  circle,
  inner sep=2pt,
  font=\Huge,
  join = by -latex
},
squa/.style={
  draw,
  inner sep=2pt,
  font=\Large,
  join = by -latex
},
start chain=2,node distance=13mm
]
\node[on chain=2]
  (x2) {$x_2$};
\node[on chain=2,join=by o-latex]
  {$w_2$};
\node[on chain=2,init] (sigma)
  {$\displaystyle\Sigma$};
\node[on chain=2,squa,label=above:{\parbox{2cm}{\centering Activate \\ function}}]
  {$f$};
\node[on chain=2,label=above:Output,join=by -latex]
  {$y$};
\begin{scope}[start chain=1]
\node[on chain=1] at (0,1.5cm)
  (x1) {$x_1$};
\node[on chain=1,join=by o-latex]
  (w1) {$w_1$};
\end{scope}
\begin{scope}[start chain=3]
\node[on chain=3] at (0,-1.5cm)
  (x3) {$x_3$};
\node[on chain=3,label=below:Weights,join=by o-latex]
  (w3) {$w_3$};
\end{scope}
\node[label=above:\parbox{2cm}{\centering Bias \\ $b$}] at (sigma|-w1) (b) {};

\draw[-latex] (w1) -- (sigma);
\draw[-latex] (w3) -- (sigma);
\draw[o-latex] (b) -- (sigma);

\draw[decorate,decoration={brace,mirror}] (x1.north west) -- node[left=10pt] {Inputs} (x3.south west);
\end{tikzpicture}
\caption{NN}
\label{fig_neuron}
\end{figure}

How can I minimize size of total figure? It is a little big for two column article.