Increasing row height of table

Question

My MWE:

\documentclass{article}
\usepackage{amsmath}
\newcommand{\sgn}{\operatorname{sgn}}

\begin{document}

\begin{table}[!htpb]
\centering
\caption{Commonly used candidate CLFs.}
\begin{tabular}{cll}
\hline \hline
CLF\# & \multicolumn{1}{c}{$V(x)$} & \multicolumn{1}{c}{$\dot{V}(x)$}              \\ \hline
1     & $\frac{1}{2}x^2$           & $x\dot{x}$                                    \\
2     & $|x|$                      & $\sgn(x)$                                     \\
3     & $\sqrt{|x|}$               & $\sgn(x)\frac{1}{2}|x|^{-\frac{1}{2}}\dot{x}$ \\
4     & $ln(x^2+1)$                & $2x\dot{x}\left (x^2 +1 \right ) ^{-1}$       \\
5     & $\left [ln(x+1) \right ]^2$              & $x\dot{x} \cdot \log[x+1](x+1)^{-1}$          \\ \hline \hline
\end{tabular}
\label{tab:CLF}
\end{table}

\end{document}

The result:

Now I don't like the spacing for the first two rows of the table, because $\dot{V}(x)$ and $\frac{1}{2}x^2$ are too close to the horizontal lines. Is there an easy way to add some vertical space while keeping the text vertically centered?