File-driven PWL Source
You can specify a text file containing time, voltage (or current) pairs into a PWL
source. The data in the text file can be either a table or a list.
Vxxx n1 n2 PWL PWLFILE='filename' [col1,[col2]] [R [=repeat]]
+ [TD=delay]
Ixxx n1 n2 PWL PWLFILE='filename' [col1,[col2]] [R [=repeat]]
+ [TD=delay]