Spectrum Software
Industrial Strength Simulation




Spectrum Software has released Micro-Cap 11, the eleventh generation of our SPICE circuit simulator.

For users of previous Micro-Cap versions, check out the new features available in the latest version. For those of you who are new to Micro-Cap, take our features tour to see what Micro-Cap has to offer.




Questions and Answers - Winter 2007


Question: Is there any way to assign a default model statement to the basic resistor component? When I place a resistor in the schematic, the MODEL attribute is blank, but I would like to have a default model assigned to that attribute so that I can define a nominal tolerance for the component. This would help me out for Monte Carlo simulations since all of my resistors would automatically have a standard tolerance defined for them.

Answer: There is a way to define a default model for the resistor, capacitor, and inductor components. The first step is to create the appropriate model statement. The model should be created in a new library file or one that the user has already created. In this case, let's call the file Default.lib and store it in the Library folder. In the Default.lib file, enter a model statement such as:

.Model Resistor Res (R=1 Lot=10% TC1=3e-3)

This will create a resistor model that assigns a 10% tolerance and a 3000ppm/degree C temperature coefficient to any resistor that references it. Any of the resistor parameters can be defined in this model. Capacitor and inductor models can also be created such as:

.Model Capacitor Cap (C=1 Lot=25%)
.Model Inductor Ind (L=1 Lot=25%)

Note that the names for these models are Resistor, Capacitor, and Inductor which match exactly with the names of the components in the Micro-Cap component library. If these models are added to a new library, the next step is to add a reference to this library into the Nom.lib file that comes with Micro-Cap. Open up the Nom.lib file from the Library folder under the main MC8 folder. In this file, add in a reference to the new library such as:

.lib "Default.lib"

Save and close the Nom.lib file. Any model statements in the Default.lib file will now be globally available within Micro-Cap. Under the Windows menu, select Component Editor. In the tree on the right, navigate to the Analog Primitives/Passive Components group and select Resistor. The information for the Resistor will appear in the editor. In the list of available options, enable the option called Assign Component Name to MODEL. When enabled, this option will assign the component name to the MODEL attribute when the part is placed in a schematic. For a resistor, the MODEL attribute would automatically be defined as Resistor which would then reference the model that was just created in the Default.lib file. Repeat for the Capacitor and Inductor components if default models are being added for these.

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