Bipolar Labels Model Tab

This tab allows basic properties of BJT transistors to be set .

The "Multiplier" field set the the BJT "area scale factor". This value multiplies appropriate model parameters to reflect identical number of devices in parallel, referred to as the "M" multiplier. The netlist simple places this number in the netlist line for the BJT, without any name. e.g.

Q1 1 2 3 QN3904 1

The "Parameter" field allows variables in the .model to be a function of parameters of each BJT instance on the schematic. Individual models are generated for each BJT using these values passed in values.

e.g.

Parameters: x=1u y=10k z=1e-3

For example:

BJT Q1 may have a parameter name set as a value of "IsScale=1.1

BJT Q1 may have a parameter name set as a value of "IsScale=0.9

With a corresponding model having a specification as:

.model npn_device npn(...iIs={1e-15*IsScale} ...)

This particular example would generate a Vbe offset between the transistor pair.

The expression between the {} may be a function, for example:

.model npn_device npn(...iIs={1e-15*IsScale/sqrt(area)} ...)

Which would reflect offsets being a function of BJT size. Monte Carlo (MC) runs use this method to automatically account for transistor offset variations.

BJT have default internal key words of "m" and area" which will be used in any expression evaluation.

Contents