Using the nophys Property

The nophys property can be applied to electrical devices and subcircuits, causing them to be ignored in the extraction system, notably in LVS. Devices that have no physical representation, such as voltage sources, have this property set by default.

By ``ignoring'' these devices, the device terminals are considered as open circuits. However, there are times when it would be useful to consider these devices as shorted. For example, suppose that one wishes to include parasitic series inductance in a resistor during simulation. However, this inductance would cause LVS to fail, since the series inductor added to the schematic has no explicit physical counterpart.

It is possible to configure the nophys property to indicate that when the electrical netlist is generated for use by the extraction system, the flagged nophys devices will be forced to have all terminals connected to the same net, i.e., the terminals are effectively shorted together. Thus, the inductor in the example above, if given this property, would disappear properly during LVS. However, when generating a SPICE netlist for simulation, these devices will be included in the netlist.

There are a number of aspects to using the nophys property.

1. The cached internal electrical netlist can be in one of two states, respecting shorted nophys or not. If there are no shorted nophys devices, both representations are the same. Functions that require one representation or another will invisibly rebuild this when needed.

2. All operations in the extraction system, including the Extract Menu functions and extraction script functions, will respect the shorted nophys property. This includes the SPICE format listings from electrical data in the Extract Menu.

   The run, deck, and other similar functions in the side menu that relate to SPICE simulation will never respect the nophys property, these devices will be treated as other devices.

3. In electrical mode, nophys devices are shown in a different color on-screen (yellow by default, the ``Terminal Color'').

4. The Property Editor will query the user whether to set the shorted option when a nophys property is added.

5. There is a Use nophys button in the Node Name Mapping editor from the side menu. This button selects whether or not to respect shorted nophys devices in the node listings. Shorted devices can obviously change the node numbering.

6. The string stored in the nophys property can either be ``nophys'' or ``shorted''. Xic sets these values according to the state.

7. There is an IncludeNoPhys script function which can be used with the existing electrical netlist access functions to provide the nophys recognition state desired.