I'm simulating a wilson current mirror and would like to plot the output impedance of the circuit. In theory, it should be as easy as Vout/Iout but I just don't have any idea how to implement it. I know it's possible because I've seen the work of my senior but I can't ask him now. Here's his plot:
Replace r1 by a huge inductance L1, inject a unit ac current between vd3 & gnd, and run an .ac simulation with a fixed frequency and a sweep of your vdd. Then plot the voltage on vd3 vs. vdd , its value should represent the output impedance.
I'm not acquainted with HSPICE, but something like this should do it:
Thanks for the help! I haven't tried your code yet as I decided to proceed with other homework but I did find a solution in the equation builder of SPICE explorer, which is to plot Vout/Iout. Sheesh, that was easy! However, I'm wondering why your method needs inductor replacement of the resistor. Also, the ac simulation is for the small signal resistance, right? I'm not sure what would be the difference if I just get the DC. Sorry, i'm such a noob
In the triode region there's not much difference. In the saturation region, however, there will be a big difference: the small signal impedance is much larger than the DC resistance, and relatively independent of Vds, which is not the case for Vout/Iout, of course.