Specifying Power and Ground Rail Characteristics

To specify the characteristics of the power and ground rails for the current bin:

Choose Flow – Abstract. The Adjust tab is the first tab in the Running step Abstract form.
In the Signal Nets section, you can control how pin shapes are adjusted during connectivity extraction to create the final required pin shapes for signal nets.
In the Power Nets section, you can control how pin shapes are adjusted during connectivity extraction to create the final required pin shapes for power nets.
Use Power rail widths, offsets and shape to specify the characteristics of the power and ground rails for the current bin.
Open the Power rail widths, offsets and shape table.
The table contains a separate row for each power rail.

The Power rail widths, offsets and shape option will be unavailable if the Create ring pins option is selected. The Create ring pins option is available only if you are processing a block.
If you try to process a block in the Core bin, the Power rail widths, offsets and shape option will lead to a long run time. To avoid this, process blocks in the Block bin.
Use Net to specify the net name in this column.
Select Shape to select from feedthru, abutment, calculate and none.
Use Width to specify the rail width (in μ) in this column.
Use Offset to specify the rail position (in μ) in this column.
You can insert or delete rows from the table by selecting the appropriate button, Add or Delete.
Check the box to the left of a row to mark it for deletion. If the table is left empty, Abstract Generator will try to determine the rail data for the Core bin, including calculating the rail and its shape. For Block and IO bins, no calculations are performed if the table is left empty. This is the default situation.

The table below describes the impact and resultant of selecting one of these values in the Shape column.

Net *Shape*	Implication	Default Setting
feedthru	The Width and Offset values do not need to be set because no calculation is performed. The terminal associated with that net will be given this shape property	Available for IO, Corner, and Block bins.
abutment		Available for IO, Corner, and Block bins.
calculate	The Width and Offset values must be entered for ALL nets because all power rail nets must be calculated.	Available only for cells in the Core bin.
none	No calculation will be performed.	Available for IO, Corner, and Block bins.

You cannot set the same power rail net more than once with different Shape values associated with it.

If the Power rail widths, offsets and shape option is set to feedthru, abutment or none, Abstract Generator will only use the specified values to set terminal properties. That is, if only one power rail net is entered into the table, that will be the only rail used to set terminal properties.

If Abstract Generator establishes that a rail can be represented by either a feedthru or an abutment rail, it will always choose the abutment shape, as shown below.

Abstract: 2001/10/31 14:51:52:

Info:     Power Rail Analysis: 

===============================================================================
Rails found
===============================================================================
rail  type    net  layer   width  offset  shape     direction   cells
-------------------------------------------------------------------------------
1     power   vdd  met1    2.5    10.87   abutment  horizontal  all
2     power   vdd  met1    5.645  7.725   feedthru  horizontal  all
3     ground  vss  met1    2.8    1.51    abutment  horizontal  all
4     ground  vss  met1    3.965  1.51    feedthru  horizontal  all

Abstract: 2001/10/31 14:51:52:

Info: Using power rails 1 and 3 to set terminal properties.These settings can be altered using the Adjust “Power rail widths and offsets”  table.

Virtuoso Abstract Generator User Guide
Product Version IC23.1, November 2023