next up previous contents index
Next: Conductor group and electrical Up: The Dump LVS Button: Previous: Using the nophys Property   Contents   Index

LVS Output File Format

For each cell comparison, the LVS system reports four levels of success.

Everything was measurable and matched.

There were device parameters which could not be compared, but all comparisons that were done matched.

In the electrical schematic, if component values are parameterized (i.e., use a token defined in a .param line or similar), or perhaps use WRspice shell expansion, the value was unavailable. In earlier releases, a value was available only if it was a numeric constant. Xic now provides limited parameter substitution during LVS (see below).

There were device parameters that differ outside of the tolerance between electrical and physical. So actually, only the circuit topological check passed.

Differences in circuit topology were detected.

The overall result for the run is the lowest level in this hierarchy reported for any cell.

The parameter database and substitution code was imported from WRspice for use during LVS and elsewhere. However, not all capability can be provided.

  1. Parameters given in subcircuit call lines are ignored in LVS, making LVS meaningless if these are given in the schematic. Parameterized instances must be remastered to unique master cells for the current LVS system.

  2. There is presently no support for macros defined in .param lines. However, single-quoted expressions are fully supported, all math operations and all relevant functions are available.

Parameter expansion works as follows:

  1. When an LVS run starts, the parameters defined in the top-level cell as param properties, and all parameters defined in .param lines found in labels on the SPTX layer in the top level cell, are placed in a table.

    In addition, the labels on the SPTX layer are searched for .option lines, and these lines are searched for a parhier option, and if found, its setting is saved. This option can be set to one of ``global'' (the default if not found) or ``local''.

  2. When comparing devices in the top-level cell, the parameter table is used to parameter substitute the value and param property strings. The resulting string should provide numerical values for comparison to the extracted physical values.

  3. When comparing in a subcell/subcircuit, the subcircuit param properties and .param labels are tabulated as for the top-level cell. This is merged with the top-level table, and is used to expand the param and value property strings of devices in the cell.

    If the parhier option was found, and it was set to local, then parameters defined in the subcircuit table will override conflicting definitions in the top level table. If parhier wasn't found or was set to global, the reverse is true - top-level definitions will override conflicting definitions in the subcell.

The output file produced by LVS contains a block of lines for each cell in the hierarchy where there is both electrical and physical information. Each block may contain several tables, which provide information about the cell and the electrical/physical associations. These tables are described below.

next up previous contents index
Next: Conductor group and electrical Up: The Dump LVS Button: Previous: Using the nophys Property   Contents   Index
Stephen R. Whiteley 2022-05-28