Linear/Ramp
The Linear
amplitude increases proportionally with time so that
\[
A(t)=V\langle{}t-t_0\rangle\quad\text{for}\quad{}t>t_0.
\]
The Ramp
amplitude is in fact a simplified version with unit slope. It adopts unit time length no matter what the
current step is and remains unity after that.
\[
A(t)=\left\{\begin{array}{rl}\langle{}t-t_0\rangle,&t<t_0+1,\\1,&t\ge{}t_0+1.\end{array}\right.
\]
The Ramp
amplitude is the default amplitude that would be used if no valid amplitude is defined.