SIMPLIS BJT Models

Any SPICE BJT model installed in the SIMetrix library can be converted for use in SIMPLIS. When a BJT is placed on a SIMPLIS schematic, a model parameter translation routine is invoked to automatically convert the SPICE model to a SIMPLIS model. During the model parameter translation process, SIMetrix/SIMPLIS automatically runs several SPICE simulations on the SPICE model and translates the SIMPLIS model parameters. After the Piecewise Linear (PWL) model parameters have been translated, the resulting BJT model will run in SIMPLIS.

In this topic:

Translating the BJT Parameters

When you place a BJT symbol on a schematic, the Translate BJT Parameters dialog opens for you to edit the default test conditions. The default test conditions are defined using the command shell menu File > Options > SIMPLIS Options.... For additional information, see SIMPLIS BJT Options.

The following table describes the Translate BJT Parameters dialog test conditions.

Translated BJT Model

Test Condition Default Value Units Description
SPICE Model Q2N2222   The SPICE model used to translate the SIMPLIS parameters.
Model type Translated   Invokes the model parameter translation algorithms.
Model level 2   Model complexity. For information on choosing the model level, see BJT Model Levels.
Peak collector current 50m A Peak collector current for this device.
Device is ON at time=0 Unchecked   Sets the initial state of this device.

SIMPLIS BJT Model Levels

The SIMPLIS BJT models support two levels: 1 and 2.

  • Level 1 uses a SIMPLIS primitive switch to model the conduction of the BJT.
  • Level 2 uses a Ebers-Moll model for the BJT.

SIMPLIS translates the SPICE model to a SIMPLIS model based on the model level chosen in the Translate NPN/PNP Parameters dialog. Although these models are internally saved as ASCII text, the following illustrations show the two model levels in a schematic form.

Level 1 Model

Level 1 models a BJT using a SIMPLIS primitive switch and a PWL base-emitter diode. This model is primarily useful if the BJT is used as a basic on/off switch, and the details of the saturation behavior are not critical.

Below is a schematic view of Level 1 model:

Level 1 models these circuit elements Level 1 Schematic
!RBE: Base-Emitter Diode modeled by a 2-segment PWL Resistor
SCE SIMPLIS Primitive switch

Level 2 Model

The Level 2 BJT model uses the Ebers-Moll BJT model.

Below is a schematic view of Level 2 model:

Level 2 models these circuit elements Level 2 Schematic
!RBC: Base-Collector Diode modeled by a 2-segment PWL Resistor
!RBE: Base-Emitter Diode modeled by a 2-segment PWL Resistor
RC: Collector Resistance
RE: Emitter Resistance
FCB: Current Controlled Current Source controlled by !RBE.
FEB: Current Controlled Current Source controlled by !RBC.
 

User-defined Models

The user-defined model uses parameters entered directly in the Edit BJT Parameters dialog without invoking the model translation algorithms. A BJT can be switched from an translated model to a user-defined model at any point; however the translated parameters are by default copied over to the user-defined parameters, replacing any user-entered values. You can disable this behavior in the SIMPLIS Options dialog by clearing the check box labeled Automatically copy translated parameters to User-defined parameter. You can access these options from the command shell menu File > Options > SIMPLIS Options.... For more information, see SIMPLIS BJT Options.

User-defined BJT Model

Parameters Default Value Units Description
Label: USER_LABEL   Any descriptive text. Cannot contain whitespace characters.
Model type: User-defined   The values in this dialog are used literally.
Collector current: 50m A Peak collector current for this device
Forward beta: 100   The forward gain of the BJT transistor
Reverse beta: 5   The reverse gain of the BJT transistor
Saturation current: 1E-15 A The transistor saturation current
Collector resistance: 0 Ω The collector resistance
Emitter resistance: 0 Ω The emitter resistance
Base resistance: 0 Ω The base resistance

User-defined model

The user-defined model is simply a level 2 model with user input of all parameters.

Below is a schematic view of a User-defined model:

User-defined models these circuit elements User-defined Schematic
!RBC: Base-Collector Diode modeled by a 2-segment PWL Resistor
!RBE: Base-Emitter Diode modeled by a 2-segment PWL Resistor
RC: Collector Resistance
RE: Emitter Resistance
FCB: Current Controlled Current Source controlled by !RBE.
FEB: Current Controlled Current Source controlled by !RBC.
 

Manually Generate and Customize BJT Models

You can customize or manually generate your own BJT models using a parameter string with multiple PARAM_NAME=PARAM_VALUE key-value pairs. The parameter names and their functions are described in the BJT Model Parameters section below. You can interpret the SIMPLIS parameter values from device datasheet specifications and curves.

You can compose the parameter string in a text editor, spreadsheet, or script. The order of the parameter names in the parameter string and the capitalization of the parameter names are irrelevant.

You can include a PROTECTED=1 key-value pair to prevent from translating a model and overwriting your manually generated parameters. The PROTECTED=1 key-value pair is not used in the simulation.  

Note: When you click on the device after adding the PROTECTED=1 key-value pair, the following message box appears to warn you that this is a hand-edited model.

To customize or generate your own BJT model, follow these steps:

  1. Create a parameter string of multiple PARAM_NAME=PARAM_VALUE key-value pairs using your preferred text editor, spreadsheet or script.
  2. Add the PROTECTED=1 key-value pair to the parameter string.
  3. Translate BJT model and place it on a schematic.
  4. Right click on the symbol and select Edit/Add Properties....
  5. Double click on the PARAM_VALUES property.
    Result: The Edit Property dialog opens. At this point, you can change individual parameters in the Value box, or replace the entire default properties with the parameter string that you created in Step 2.
  6. To replace the entire string, follow these steps:
    1. Click in the Value box and type Ctrl A to select all of the existing parameter string, and press Delete.
    2. Copy the parameter string you completed in Step 2 and paste into the Value box.
    3. Click Ok.
  7. To change the name of your customized model, double click the VALUE property in the Edit Properties dialog, and change the name in the Value box.
  8. To return to the schematic, click Ok.
Alternately you can write the PARAM_VALUES property to the symbol using the Prop command in the command line with the following syntax:   
prop PARAM_VALUES parameter_string
where parameter_string is the set of key-value pairs that you created in Steps 1 and 2 above.
Important: Since parameter_string contains spaces, the entire string must be enclosed in double quotes.

BJT Model Parameters

The following tables detail the parameters which define the electrical behavior of the BJT model. Several other parameters in the PARAM_VALUES property have no effect on the electrical behavior of the model. These parameters are used to populate the Translate BJT Parameters dialog box.

Model Parameters

Parameter Names Default Value Description
USE_EXTRACTED 1 This parameter switches to model to either use the Translated parameters, or the User-defined parameters. If you set this to 1, the model will use the parameters in this table.
Note: This parameter name is a misnomer carried over from the other semiconductor devices. There are no Extracted BJT models in SIMPLIS.
.
LEVEL 2 The level parameter. See SIMPLIS_BJT_Model_Levels for details.
ICE_PEAK 50m Peak collector current for this device
BF 100 The forward gain of the BJT transistor
BR 5 The reverse gain of the BJT transistor
IS 1E-15 The transistor saturation current
RC 0 The collector resistance
RE 0 The emitter resistance
RB 0 The base resistance

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