Plotting Gm/Id with LTSpice

It is useful to plot Gm/Id for transistors to help with choosing how to bias a transistor. It is not straightforward in LTSpice since Gm is not an output parameter in LTSpice. Below describes how to plot Gm/Id using LTSpice and does so with some generic Mosfet models.

The Mosfet models are from the Predictive Model Technology website. They are all BSIM4 models and are from 4 different technology nodes: 130nm, 65nm, 32nm and 22nm models.
The channel lengths were set to 190nm, 100nm, 48nm and 33nm respectively for the different technology nodes.
The mosfet library files are : BSIM4_130.lib BSIM4_65.lib BSIM4_32.lib BSIM4_022.lib

The results are shown below

To get the above results, the following LTSpice schematic and plot files were used
gm-id.asc
gm-id.plt

Notes:

- Due to gate leakage, Is(M1) was found (rather than Id(M1)) as the gate leakage can be significant when VG is near zero and Ids is very small.
- d(Is(M1)) is the derivative of Is(M1) so it is equal to gm