The standard WRspice device library contains models for the semiconductor devices listed in the table below. Each of these devices references a corresponding model supplied on a .model line (see 2.13). The model supplies most of the parameters that specify device behavior. If a corresponding model is not found, usually a warning is issued and a default model is used.
|Bipolar Junction Transistor||bjt||q|
|Junction Field-Effect Transistor||jfet||j|
Each device element line contains the device name, the nodes to which the device is connected, and the device model name. In addition, other optional parameters may be specified for some devices: geometric factors and an initial condition.
The area factor used on the device lines determines the number of equivalent parallel devices of a specified model. The affected parameters are marked with an asterisk under the heading ``area'' in the model descriptions. Several geometric factors associated with the channel and the drain and source diffusions can be specified on the MOSFET device line.
Two different forms of initial conditions may be specified for some devices. The first form is included to improve the dc convergence for circuits that contain more than one stable state. If a device is specified off, the dc operating point is determined with the device internal terminal voltages (not external node voltages!) for that device set to zero. This effectively makes the device an open circuit. After convergence is obtained, the program continues to iterate to obtain the exact value for the terminal voltages. If a circuit has more than one dc stable state, the off option can be used to force the solution to correspond to a desired state. If a device is specified off when in reality the device is conducting, the program will still obtain the correct solution (assuming the solutions converge) but more iterations will be required since the program must independently converge to two separate solutions. The .nodeset line serves a similar purpose as the off option. The .nodeset directive is easier to apply and is the preferred means to aid convergence in this situation.
The second form of initial condition is specified for use with transient analysis. These are true initial conditions as opposed to the convergence aids above. See the description of the .ic line and the .tran line for a detailed explanation of initial conditions.