gm/Id Method and how to plot the graphs

[Supersnail]

Hi everyone,

I'm currently trying to use the gm/Id method in order to design an OTA.
Therefore, I want to plot the required graphs for this method that correspond to the technology I use.
Here is what I do :
For the Id/(W/L) graph versus gm/Id, I plot Id vs Vgs and get gm by taking the gm vs vgs derivative and I do that for a fixed width and different transistor lengths.
My problem is that gm/Id graphs vary with length and so how am I supposed to plot Id/(W/L) graph versus gm/Id for different lengths on the same graph when I have different X axis ?
Same thing for fT vs. gm/Id.

Thanks for your answers

 

[erikl]

My problem is that gm/Id graphs vary with length and so how am I supposed to plot Id/(W/L) graph versus gm/Id for different lengths on the same graph when I have different X axis ?
Same thing for fT vs. gm/Id.

Not different X axes - you get different curves for different lengths, s. these example curves (pp. 13 & 19): View attachment gm-Id-example_curves.pdf