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Extraction Methodology and Overview

To use the extraction capability, one typically first designs the circuit in electrical mode, then produces a corresponding layout in physical mode. The Show Groups command is a useful diagnostic aid, as it shows the group numbers of conducting objects (a group number is analogous to a circuit node number). Objects which have been partitioned, as have been clipped due to a Conductor Exclude directive, have multiple group assignments, and the partition boundaries are shown in the Show Groups command.

When the Select Groups button is active, clicking on an object or a partition will select the entire group to which the object or partition belongs, if the command was entered while in physical mode.

There are cases where one starts with a layout, and it is desirable to generate a schematic. There are also situations where the physical and electrical designs are generated in separate files, and it is desirable to merge these into a single file. Xic has provisions to assist in these cases.

Schematics can be generated in various ways. The schematics that are machine-generated by Xic have each device individually connected to gnd or tbar terminals, so there are no wires. These schematics are electrically correct, but lack human-readability and aesthetics. They serve, however, as a starting point if the user wishes to rearrange the devices and add wires as in a normal schematic.

A schematic can be generated from a SPICE file with the Source SPICE button. This can create devices and subcircuits as needed. Existing devices will have properties updated with values from the SPICE file.

Similarly, the Source Physical button will update the schematic from an intermediate SPICE file extracted from the physical layout. Existing devices will have properties updated with values extracted from the physical layout, and missing devices and subcircuits are added.

The Read Layout File panel from the Convert Menu is used to copy either the electrical or physical part of another cell into the current cell. It is able to extract this information from cell definitions within an archive file. This can be used to combine separate electrical and physical designs into a single hierarchy.

Separate commands are available for generating netlist files from the physical and electrical data. The Dump LVS command performs the layout vs. schematic comparison, and prints errors in a file and on-screen.

The Dump Phys Netlist command in the Extract Menu generates a connectivity listing extracted from the physical database. This includes a listing of extracted devices, in various formats. One format is SPICE, so that the Dump Phys Netlist command can be used to generate a SPICE listing extracted from the physical layout.

Commands in the Extract Menu also work with the node mapping facility for SPICE output. It is often necessary to know the name of specific circuit nodes in a SPICE file, which by default is not possible as Xic assigns then internally. The node mapping facility, controlled with the nodmp button in the electrical mode side menu, allows the node tokens to be preassigned.


next up previous contents index
Next: The Extraction View Button: Up: The Extract Menu: Extraction Previous: Format Library File   Contents   Index
Stephen R. Whiteley 2012-04-01