Plotting required waveforms in LTSPICE XVII

[garvind25]

Hi,



I am trying to characterize the transistors for gm/Id design methodology. I am using LTSPICE for it and have the following queries. I hope someone can answer them:



** Can I define a constant capacitance value in LTSPICE such as Cox = 8.5fF/u^2 such that after simulation, I can manipulate the graph to plot expressions like fT = gm/2*3.14*W*L*Cox? If I simply use the magnitude of Cox as 8.5f, though I get the graph, the unit of the Y-axis isn’t frequency (as it should be). The x-axis is Vgs (swept by a dc sweep command).



** As I know, after the simulation, I can manipulate the graph to plot expressions on the y-axis (such as for fT as in above query). Is it possible to plot graphs with expressions on both Y axis and X axis?. For eg. how to plot a graph of fT vs gm/Id (where the fT expression will be on y axis and gm/Id expression on x axis).



Thanks in advance,

Arvind Gupta

 

[stenzer]

Hi,

the unit of the Y-axis isn’t frequency (as it should be)

as you are skipping the unit, you will not get Hz as a result. Here, LTspice does not know you are dealing with Farads, and consequently you are missing your 1/s term ([F] = [C/V] = [A • s / V]).

Is it possible to plot graphs with expressions on both Y axis and X axis?

Have you considered to create an XY plot? Make a RMB click on the x-axis and change the quantity which should be plotted, see below.

BR