\begin{tikztimingtable} [timing/d/background/.style={fill=white},
    timing/lslope=0.2, xscale=1.80, yscale=1.0,]
       {\small \rmfamily CK\_t} & 
       L H L H L H L H L H L H L H L H L\\
       {\small \rmfamily S1} & 
       0.5L H H L L H H L L H H L L H H L L 0.5H\\
       {\small \rmfamily S2} & 
       0.5L H L H L H L H H H H H L L L L L 0.5H\\
  \extracode
  \begin{pgfonlayer}{background}

      %\timemeasuup{P1}{P5}{-4.0}{\small $t_{RC} = t_{RAS} + t_{RP}$}
      %\timemeasuup{P3}{P6}{-2.0}{\small $t_{BURST}$}
      %\timemeasure{P2}{P6}{ 5.0}{\tiny $t_{RTP}$}
      %\timemeasure{P2}{P3}{ 7.0}{\small $t_{CL}$}
      %\timemeasure{P1}{P4}{ 9.0}{\small $t_{RAS}$}
      %\timemeasure{P4}{P5}{ 9.0}{\small $t_{RP}$}
      %\timemeasure{P7}{P4}{11.0}{\small $t_{RTP}$}
      %\timemeasuup{P2}{P7}{-2.0}{\small $t_{CCD}$}

    % Add vertical lines
    \begin{scope}[semitransparent,semithick]
      \vertlines[gray]{1.1,2.1,...,16.1}
    \end{scope}
 \end{pgfonlayer}
\end{tikztimingtable}%