Method for placing operational cells in a semiconductor device
View Patent ↗There is provided a method of placing a plurality of operational cells of a semiconductor device within a semiconductor layout, comprising determining timing data for each of the plurality of operational cells, determining switching activity from RTL or design constraints for each of the plurality of operational cells, determining power grid switch locations relative to each of the plurality of operational cells, deriving a cost function based upon the determined timing data, determined switching activity from RTL/design constraints and determined relative power grid switch locations and initially placing the plurality of operational cells according to the derived cost function.
1. A method comprising:
initially placing a plurality of operational cells of a semiconductor device within a semiconductor physical layout;
determining timing data for each of the plurality of operational cells;
determining, by a computer, switching activity from a logic description or design constraints for each of the plurality of operational cells;
determining power grid switch locations relative to each of the plurality of operational cells;
deriving a cost function based upon the determined timing data, switching activity and power grid switch locations;
initially, by the computer, placing the plurality of operational cells at positions which are dependent on the derived cost function;
determining an estimated power loss (IR drop) value for each of the plurality of operational cells when the semiconductor device will be in use, wherein the estimated IR drop is based on a number of the plurality of operational cells that switch simultaneously;
identifying operational cells having an estimated IR drop value above a predetermined threshold; and
re-placing identified operational cells within the semiconductor layout to reduce IR drop.
2. The method of claim 1 , wherein determining an estimated IR drop value for each of the plurality of operational cells when the semiconductor device will be in use, comprises determining a worst-case maximum IR drop value.
3. The method of claim 1 , further comprising determining if the identified operational cells having an estimated IR drop value above a predetermined threshold are on a timing-critical path, wherein:
if the identified operational cells are on a timing-critical path, the identified operational cells are re-placed within the semiconductor physical layout to reduce IR drop; or
if the identified operational cells are not on a timing-critical path, the identified operational cells are left in their existing placement.
4. The method of claim 3 , wherein identifying operational cells having an estimated IR drop value above a predetermined threshold further comprises:
identifying the estimated IR drop value dependent upon switching activity of the operational cells during use.
5. The method of claim 3 , wherein identifying operational cells having an estimated IR drop value above a predetermined threshold further comprises:
identifying operational cells having an estimated IR drop value above a predetermined threshold located in the semiconductor layout in one or more switching islands, wherein a switching island comprises a group of operational cells switching at substantially the same time and located adjacent one another.
6. The method of claim 5 , wherein a switching island is further defined by a proximity of the respective operational cells to the power grid switch locations.
7. The method of claim 1 , further comprising determining operational cells having the same switching group and dependent thereon, distances between operational cells of the same group.
8. The method of claim 1 , further comprising determining a re-placement based upon any one or more of:
switching activity of the identified operational cells from vectors;
power rail location information; and
timing data.
9. The method of claim 8 , wherein re-placement of the identified operational cells comprises:
swapping a location of an identified operational cell having an estimated IR drop value above a predetermined threshold with a location of another operational cell that is not in a same switching group; or
swapping a location of an identified operational cell having an estimated IR drop value above a predetermined threshold with a location of another operational cell that is part of a less-critical timing path.
10. The method of claim 9 , further comprising, after re-placement of identified operational cells:
re-determining an estimated IR drop value for each of the plurality of operational cells during use of the semiconductor device; and
if the re-determined maximum IR drop for at least one operational cell is above a predetermined threshold, carrying out another re-placement.
11. The method of claim 1 , wherein the method of placing operational cells comprises a method of optimising an initial placement of operational cells in a semiconductor physical layout.
12. A method of re-placing a plurality of operational cells of a semiconductor device within a semiconductor physical layout, comprising:
determining, by a computer, a simulated power loss (IR drop) value for each of the plurality of operational cells when the semiconductor device will be in use;
identifying, by the computer, operational cells having a simulated IR drop value above a predetermined threshold;
determining whether the identified operational cells have a high estimated IR due to simultaneous switching, and if so, the method further comprising:
determining timing data for each of the plurality of operational cells;
determining switching activity from a logic description or design constraints for each of the plurality of operational cells;
determining power grid switch locations relative to each of the plurality of operational cells;
deriving a cost function based upon the determined timing data, switching activity and power grid switch locations; and
re-placing identified operational cells within the semiconductor layout to reduce IR drop;
wherein the method further comprises:
determining a simulated IR drop value for each of the plurality of re-placed operational cells when the semiconductor device will be in use; and
determining whether each re-placed operational cell IR drop value is below a predetermined maximum IR drop threshold.
13. A method of manufacturing a semiconductor device, comprising carrying out the method of claim 12 , and manufacturing the semiconductor device from the semiconductor physical layout.
14. The method of claim 12 , further comprising determining operational cells having the same switching group and dependent thereon, distances between operational cells of the same group.
15. A method of initially placing a plurality of operational cells of a semiconductor device within a semiconductor physical layout, comprising:
determining timing data for each of the plurality of operational cells;
determining, by a computer, switching activity a logic description or design constraints for each of the plurality of operational cells;
determining power grid switch locations relative to each of the plurality of operational cells;
deriving a cost function based upon the determined timing data, switching activity and power grid switch locations;
initially, by the computer, placing the plurality of operational cells at positions which are dependent on the derived cost function; and
swapping a location of an identified operational cell having an estimated power loss (IR drop) value above a predetermined threshold with a location of another operational cell that is not in a same switching group; or
swapping a location of an identified operational cell having an estimated IR drop value above a predetermined threshold with a location of another operational cell that is part of a less-critical timing path.
16. The method of claim 15 , wherein the method of placing operational cells comprises a method of optimising an initial placement of operational cells in a semiconductor physical layout.
17. The method of claim 15 , further comprising:
re-determining an estimated IR drop value for each of the plurality of operational cells during use of the semiconductor device; and
if the re-determined maximum IR drop for at least one operational cell is above a predetermined threshold, carrying out another re-placement.
18. The method of claim 15 , further comprising:
determining an estimated IR drop value for each of the plurality of operational cells when the semiconductor device will be in use, wherein the estimated IR drop is based on a number of the plurality of operational cells that switch simultaneously;
identifying operational cells having an estimated IR drop value above a predetermined threshold;
re-placing identified operational cells within the semiconductor layout to reduce IR drop.
19. A method of manufacturing a semiconductor device, comprising carrying out the method of claim 15 , and manufacturing the semiconductor device from the semiconductor physical layout.