multisim: creating 4-terminal MOSFET models / Multisim equivalent to SPICE .OP directive

[dbeams]

I am hoping to have juniors in my Electronics II class do some design and simulation of analog CMOS circuits--specifically, simple op amps--but I have run into two brick walls with Multisim.  

1.  I need to create my own four-terminal MOSFET models.  I have the parametric values for LEVEL 1 models for both NMOS  and PMOS devices.  However, my attempts to create my own devices have met with very limited success. 

--My first approach was to instantiate a four-terminal virtual device, then to edit the model and save the component to my user database.  However, the changes I make to the model are not saved...when I instantiate one of my newly-created parts, the device model is the default NMOS or PMOS model.  

--My second approach was to use the component wizard.  I was able to create a part, import a schematic symbol, edit the model, and save the component.  And the model matches my model when I instantiate the part!  So far, so good.  However, the Properties tab of the new device does not include the instance information that one uses to override the default (or model values) of length, width, or multiplicity.  

What I want to do is create base models of both PMOS and NMOS four-terminal devices with some nominal W/L ratios, but which I could override as required.  For example, suppose my base model of an NMOS device had a 4:1 W/L ratio but my design of a common-source amplifier needs 40:1.  I really do not want to have to place ten devices in parallel if I can just place one device and alter its multiplicity.  It appears that my only option at the moment is to create a number of MOSFETs of varying W/L ratios using the component wizard.

2.  I need to find gm, gmb, and ro information from the small-signal models of the MOSFETs in my designs.  The SPICE means for this is an .OP statement which causes small-signal model information for active devices to be printed on the SPICE output file.  But I have searched unsuccessfully for the Multisim equivalent.  Come to think of it, I have not yet discovered the Multisim equivalent of the SPICE output listing.

Any ideas?  Anyone who could make useful suggestions will earn my undying gratitude.  No money will change hands, but you will help make the world a better place.

[Tien_P]

Hi,

The following knowledge base provides general information about MOSFET model syntax:

http://digital.ni.com/public.nsf/allkb/2977F43588E1C460862572F3005693A6

A MOSFET model is a core SPICE model and it is a 4-terminal model. You can use the component wizard and import a core model. For a MOSFET this is the model:

.model NMOSDefault NMOS()

Between the brackets, I didn't add any parameter  which means Multisim will use the model default value.

You can use the Component wizard to create a default model and save it to your database. When you get to the symbol to model mapping stage in the Component Wizard, this is the model pin order: D G  S B,  terminal D is 1.

If you want to use the length and width parameter, you should subckt model.

A line beginning with "M"  is a SPICE command to call a MOSFET core model and on this line, you can declare the length and width for the MOSFET.

M1 D G S S B4 W=1 L=1

2. The Multisim DC Operating Point analysis is the same as the .op statement.