Aprisa goes beyond the conventional methods to support more comprehensive methodologies to better address IR-drop issues at advanced nodes, including: <\/p>\n\n\n\n
- IR-driven place & route flow <\/li>
- Power grid enhancement: strengthening the power grid over hotspot regions <\/li><\/ul>\n\n\n\n
Let\u2019s look at these methods more closely. <\/p>\n\n\n\n
IR-driven place and route flow<\/strong>\u00a0<\/h3>\n\n\n\n
Place optimization<\/strong> \u2013 During place optimization, Aprisa\u2019s Legalizer performs IR-driven placement, which involves dispersing IR hotspots by spreading out the cells to reduce the total peak current. Subsequent optimizations can recover any timing disturbance introduced by the IR-driven placement. <\/p>\n\n\n\n
By default, the IR-driven placer identifies hotspots based on a certain IR-drop ratio. For timing critical designs, the maximum IR-drop ratio can be lowered to minimize the impact on timing. <\/p>\n\n\n\n
Post-CTS optimization <\/strong>\u2013 During post-CTS optimization, Aprisa performs congestion-driven global placement and IR-driven legalization. It addresses peak currents based on timing windows to minimize dynamic IR violators and avoids, by default, large cell displacements of registers and clock cells. <\/p>\n\n\n\n
IR-driven incremental legalization <\/strong>\u2013 At any stage during the place and route flow, designers can easily run IR-driven incremental legalization. Towards the later stages in the implementation flow, this option can be used to address minor IR violations by using a lower maximum IR-drop ratio that ensures minimal disturbance to the layout. <\/p>\n\n\n\n
Table 1 shows an example of how Aprisa improved the \u201cPeak Combined IR-drop\u201d by about 7.2% when running the IR-driven flow vs. the regular flow. This is significant for designs that are sensitive to IR-drop. <\/p>\n\n\n
\n![\"\"](\"https:\/\/blogs.sw.siemens.com\/wp-content\/uploads\/sites\/62\/2022\/08\/IR-driven-flow-table1-600x98.jpg\")
Table 1. Peak IR-drop improvement with IR-driven place and route flow.<\/figcaption><\/figure><\/div>\n\n\n Power grid enhancement<\/strong><\/h3>\n\n\n\n
Typically, IR hotspots are dominated by high switching cells such as clock cells, or high current cells such as big repeaters and registers. The hot spots can span across multiple rows and columns of the power\/ground (PG) network. Moving clock cells and registers can improve the IR hotspot, but can severely impact timing\/clock QoR. Locally moving the cells with high current demand might help to improve the severity of the specific hotspot but can move the hotspot to a different local region.<\/p>\n\n\n\n
These factors mean that IR-driven legalization alone may not be able to address all the hotspots. When that is the case, Aprisa can strengthen the pre-existing power grid. Aprisa\u2019s Power Grid Enhancement utility adds additional stripes in selected areas to enhance the PG connections. In addition to being very effective, Power Grid Enhancement utility is: Automatic, easy to use, DRC aware, and timing aware<\/strong><\/p>\n\n\n
\n![\"\"](\"https:\/\/blogs.sw.siemens.com\/wp-content\/uploads\/sites\/62\/2022\/08\/IR-driven-flow-power-grid-enhancement-600x540.jpg\")
Figure 1. Aprisa\u2019s Power Grid Enhancement is shown for one layer (M3 in blue) over marked hotspot region (green square).<\/figcaption><\/figure><\/div>\n\n\n Figure 1 shows an enhanced PG network example. In this case, the database is already routed but Aprisa can add PG shapes from a pre-existing PG network over the hotspot region with just a couple of standalone user commands.<\/p>\n\n\n\n
The Power Grid Enhancement utility has several options, the most commonly used options:<\/p>\n\n\n\n
- Control the spacing to timing-critical nets while adding additional PG shapes<\/li>
- Define custom spacing rules for specific nets<\/li><\/ul>\n\n\n\n
While the utility allows lots of customization, users can just use the
-timing_driven<\/code> option, which ensures the timing profile of the critical nets is not degraded.<\/p>\n\n\n\nDebugging IR results<\/strong><\/h3>\n\n\n\n
Aprisa offers various ways for debugging IR-drop issues. It has a user-friendly power network map in the GUI browser that can be helpful for analyzing results. You can also use the GUI to see the high peak current values of the cells (Figure 2). <\/p>\n\n\n
\n![\"\"](\"https:\/\/blogs.sw.siemens.com\/wp-content\/uploads\/sites\/62\/2022\/08\/IR-driven-flow-debug.png\")
Figure 2. Cells with peak current values.<\/figcaption><\/figure><\/div>\n\n\n Don\u2019t let IR drop wreak havoc on your designs. Aprisa uses the conventional methods to minimize IR drop and also a full IR-driven flow based on an innovative software architecture and unified data model shared through the entire flow. Aprisa offers fast, accurate design closure and ease of use for today\u2019s advanced node designs.<\/p>\n\n\n\n