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Symmetry Constraints For Double Height Cell Placement

IP.com Disclosure Number: IPCOM000010436D
Publication Date: 2002-Dec-02
Document File: 16 page(s) / 80K

Publishing Venue

The IP.com Prior Art Database

Abstract

Symmetry constraints are a way of enforcing symmetry between the sub-cells of a double height cell. Identical blocks of logic from the netlist are paired together. The elements of each pair are placed with the same orientation in the same column in separate sub-cells. The paired blocks of logic are then treated as a group (i.e. one combined entity) when determining their position relative to other blocks of logic from the netlist.

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Page 1 of 16

1. Descriptive Title

Symmetry Constraints for Double Height Cell Placement

2. Problem

Double height cells require symmetry between sub-cells for better routability, smaller cell size and better electrical properties. Also, making use of symmetry between sub-cells significantly reduces the placement search space.

3. Solution

Symmetry constrains are a way of enforcing symmetry between the sub-cells of a double height cell. Identical blocks of logic from the netlist are paired together. The elements of each pair are placed with the same orientation in the same column in separate sub-cells. The paired blocks of logic are then treated as a group (i.e. one combined entity) when determining their position relative to other blocks of logic from the netlist.

4. Figure Show key components of flow, software, idea.

Page 2 of 16

Symmetry Constraints for Double Height Cell Placement

Page 3 of 16

Background

Double height cells are cells that span two rows of the place-and-route's rows of standard cells

TOP

Double-

Height Cell

Bottom

Page 4 of 16

Background

Cadabra placement group transistor by functions: Tiles

Place tiles

Page 5 of 16

Background

There are several options to place mosfets onto top/bottom halves of a double height cell

Partition transistor netlist and do regular single height placement on each half of the cell Cutting linear placement in a half Producing double height placement from single height tiles - this is our approach!

Etc.

To find the "best" double height placement, you have to consider all possible placements (solution space)

Page 6 of 16

Problem

Double height cells require symmetry between top/bottom halves for:

Better routability Smaller cell size Better electrical properties

Side benefit: it reduces the placement search space

Page 7 of 16

Solution

Symmetry constraints are a way of enforcing symmetry between the top/bottom halves of a double height cell Identical blocks of logic from the netlist are paired together

The elements of each pair are placed with...