Defining MOS with attributes or .model, setting level

I’m simulating a simple CMOS inverter and have some questions.

  1. Why can’t I use the attributes to declare model parameters? When I do (see inv_with_attributes.qsch), it tells me Warning: Ignoring unknown instance parameter for all the attributes. When I create a .model statement, it doesn’t give me these errors.

  2. I see the default oxide thickness is 15nm. Why then, when I simply define TOX that way, does Qspice say TOX=1.5e-08 which is smaller than can is be realistically modeled with a level 1 equations.

  3. Related to (2), why does it think I’m using a level 1 model when I’ve explicitly said level 3? How do I know I’m setting the level correctly?

inv_with_attributes.qsch (4.6 KB)
inv_with_model.qsch (4.5 KB)

Ans 1 : Instance Parameter (in attribute) and Model Parameters (in .model) are two different things. Some devices have common instance and model parameters, for example, Voltage Controlled Switch (S-device), but not NMOS/PMOS. Refer to Help to differentiate what can be Instance and what can be Model parameters.

Here is a link you can download level 3 MOS3 and level 7 BSIM model
https://user.eng.umd.edu/~newcomb/bicmosis.htm

I simply ran test for bsim3.lib (rename to bsim3.txt) and run simple example in Qspice.
bsim3.txt (16.7 KB)
MOS Level=3 - MOS3.qsch (2.9 KB)
MOS Level=7 - BSIM3.qsch (2.9 KB)

I have no experience in using these model, just came across simple testing for studying purpose. But I think you may take it as your example and check if it help in seeking answer in your Q2 and Q3.

1 Like