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Electrical Mode Properties

In electrical mode, only properties with certain values and data can be entered, and only to objects corresponding to library devices or subcircuit instances.

These properties can be applied to devices and subcircuit instances:
Name Value
name the device name given to SPICE
param the device initial condition and other parameters for SPICE
other anything, not used internally
nophys either ``nophys'' or ``shorted''

These properties can be applied to device instances only:
Name Value
model the name of a SPICE device model
value the device value as given to SPICE

This property can be applied to subcircuit cells only.
Name Value
virtual always ``virtual''

In addition, internally generated properties, such as node numbers, are listed in the display.

In a device or subcircuit, there can be at most one of each of the properties mentioned above, with the exception of other properties of which there can be an arbitrary number.

The name property will always be present. Assigning a name property means that the assigned name will be used in SPICE listings, otherwise Xic will generate a name for the device. Deleting a name property simply deletes the user's name, if any.

The other properties are not used internally, and the text can be any string. They are often useful for storing alternate strings for the model, value, and param properties.

The nophys property is a flag to indicate that the device or subcircuit has no physical representation in the layout, and will be ignored in LVS testing. If the value is the keyword ``shorted'', the terminals of the device or subcircuit will be logically shorted together for LVS testing. Otherwise, the terminals will be taken as open circuits.

The virtual property is a flag that indicates that a subcircuit cell will not appear in netlist output, so that the cell is a ``placeholder'' and the actual subcircuit definition will be obtained from another source (such as a vendor library file).

The device line in a SPICE file looks like:
(name) (nodes ...) (value or model) (param)

The name field is either the name property given, or an internally generated name. The nodes field is internally generated, using mapped or internally generated node names. Only one of the value or model properties is used. If both are set, the model has precedence. This is followed by the param (initial condition and parameters) string, if present. The precise format of the strings for each of these properties is determined by the device being set, and the details of the version of SPICE being used. The first letter of a name property should be the character used to key the device type to SPICE. The user should be familiar with these requirements.

In addition, it is possible to apply the param property to subcircuit instances, and also to the current cell with the Cell Properties command. This provides support for subcircuit parameterization, which is available in WRspice and some other simulators.

Unlike all other properties, after changing a param property of a cell, using the Cell Properties Editor or otherwise, all instances of that cell are examined and the param property of the instances may be updated.

  1. If an instance has no param property or the instance param property text is the same as the old cell param property text, or there was no previous cell param property, the instance property is updated to be a copy of the new cell param property.

  2. If a cell param property is deleted, param properties found in the instances with matching text will also be deleted.

Here is a brief description of how to use parameterization. Suppose that you are editing a cell that contains a resistor, and you wish to parameterize the resistor. Give the resistor a value property consisting of some word, say ``rshunt''. Using the Cell Property Editor, give the cell a param property something like ``rshunt=2.5''. This will give the resistor a default value of 2.5 ohms. Editing another cell, place two instances of the previous cell. Note that ``rshunt=2.5'' appears in a label next to each instance. Select one of the labels, and using the label editor change the string to ``rshunt=1.25''. This will change the resistor value in that instance (only) to 1.25 ohms.


next up previous contents index
Next: Physical Mode Pseudo-Properties Up: Cell and Object Properties Previous: Cell and Object Properties   Contents   Index
Stephen R. Whiteley 2012-04-01