SPICE “V” element with “EXP” option generates an exponential pulse signal.
The syntax of “EXP” is as follows.
Berkeley SPICE2, HSpice, PSpice, XSpice, LTspice
Vxxx n+ n- EXP(V1 V2 [TD1] [TAU1] [TD2] [TAU2])
V1:initial value [V]
V2:pulsed value [V]
TD1:rise delay time [s]
TAU1:rise time constant [s]
TD2:fall delay time [s]
TAU2:fall time constant [s]
V1 N001 0 EXP(0 1 10m 20m 10m 20m)
The symbol of LTspice’s “V” element with “EXP” option is “voltage” which is in “C:\Users\Username\Documents\LTspiceXVII\lib\sym” directory. If you want to set the parameters of that by GUI, click “Advanced” button on “Component” menu window and check “EXP(V1 V2 Td1 Tau1 Td2 Tau2)” in “Functions” setting.