# Special Parts

In this topic:

## Initial Conditions

Initial conditions force a node to a fixed voltage or current during the calculation of the DC bias point. There are two types of initial condition namely soft and hard. Soft initial conditions apply a voltage through a fixed resistance. Hard initial conditions, apply a voltage directly without any resistance.

### To Place a Soft Initial Condition

1. Select menu Place > Connectors > Initial Condition.
2. Place device at the desired location then select and press F7. Enter a suitable voltage.

### To Place a Hard Initial Condition

1. Select menu Place > From Symbol Library
2. Select device Connections $\rightarrow$ Ics and Nodesets $\rightarrow$ Initial Condition (Hard).
3. Place device at the desired location then select and press F7. Enter a suitable voltage.

### Notes

Soft initial conditions are implemented using the .IC control and will also correctly apply an initial condition when Skip DC bias point is specified for a transient analysis. The driving resistance for a soft initial condition is 1 by default but can be altered using the ICRES simulator option. To do this, add .OPTIONS ICRES=nnn to the F11 window (see Manual Entry of Simulator Commands).

Hard Initial conditions are implemented using a voltage source with the DCOP parameter specified. This feature is proprietary to SIMetrix and is not compatible with other SPICE simulators. Refer to the Simulator Reference Manual/Analog Device Reference/Voltage Source for more information on voltage sources and the DCOP parameter.

## Nodesets

Nodesets are used to help convergence and also to coerce a particular state for circuits that have more than one possible DC solution. More information about nodesets is given in the Simulator Reference Manual/Command Reference/.NODESET.

### To Place a Nodeset

1. Select menu Place > Connectors > Nodeset
2. Place device at the desired location then select and press F7. Enter a suitable voltage.