You could use addition or multiplication. For example:
Code:analog begin
offset = transition(enable, 0, 10n);
sine = ampl*sine(6.28*freq*$abstime);
V(out) <+ offset + sine;
end
Code:analog begin
on = transition(enable, 0, 10n);
sine = on*ampl*sine(6.28*freq*$abstime);
V(out) <+ sine;
end
-Ken