Simulation Model

This is where you enter the component's simulation model. This step appears for components with simulation models only.

The simulation model entered must be comprised of a .model command or a .subckt command.

.model command

A .model command is limited to defining parameters for a primitive SPICE device such as a diode or a BJT. Manufacturers of discrete parts such as BJTs often use a single .model statement as the entire model for the discrete part.

A .model statement follows the syntax:

.model <any model name> <specific device name> <a list of parameters>

For example, the following is a valid model for an N-type BJT:

.model 2X1234 NPN
+IS=1.91e-15 BF=149.5 NF=0.91 VAF=10
+IKF=0.51821

The + character on each line is SPICE syntax for a continuation of a statement on a preceding line.

  You can paste this model text into the Model data field. This would constitute a complete and valid model.

  If you are using only a single .model statement as the model, you may not include any other text except for comments (lines that start with *) and white space.

.subckt command

A .subckt command is simply a wrapper for creating arbitrary SPICE models. It allows more flexibility in defining models than a standalone .model command and, because it is a wrapper, it shields the internal nodes and names from conflicts in a larger circuit where it is ultimately used. A .subckt is typically used for defining models, such as opamps, which cannot be defined using a single .model statement.

A .subckt statement follows the syntax:

.subckt <any model name> <a list of ports>
Arbitrary model data
.ends

Every .subckt command must have a matching .ends command, which encapsulates the model.

For example, the following is an L-C-L filter wrapped-up using a .subckt:

.subckt LCL_filter left gnd right
L1 left mid 50u
C1 mid gnd 120u
L2 mid right 50u
.ends

To apply a .subckt model, load or paste it into the Model data field in its entirety.

Notes:

• Except for comments (lines that start with *) and white space, there must be nothing outside of the outer-most .subckt. For example, the following is not a valid model:

  .tran 1u
  Vin in 0 24
  .subckt LCL_filter left gnd right
  L1 left mid 50u
  C1 mid gnd 120u
  L2 mid right 50u
  .ends

• If you have a model that is comprised of dependent .subckt ensure to the dependent .subckts into the outer-most .subckts.

  For example, suppose you have the following model:

  .subckt model1 1 2 3
  Q1 1 2 3 tran
  X1 1 7 Rfb
  .model tran npn(bf=100)
  .ends

  .subckt Rfb 1 2
  R1 1 2 10k
  .ends

  In this case, model1 has a dependency on Rfb1. You should therefore place Rfb into model1 as follows:

  .subckt model1 1 2 3
  Q1 1 2 3 tran
  X1 1 7 Rfb
  .model tran npn(bf=100)

  .subckt Rfb 1 2
  R1 1 2 10k
  .ends

  .ends

Refer to the Multisim SPICE Reference section for more information on .model and .subckts.

Refer to the table below as needed: