{"id":26371,"date":"2025-06-04T20:02:50","date_gmt":"2025-06-04T20:02:50","guid":{"rendered":"https:\/\/wattsemi.com\/?p=26371"},"modified":"2025-06-05T18:41:54","modified_gmt":"2025-06-05T18:41:54","slug":"ppa-optimization-strategies","status":"publish","type":"post","link":"https:\/\/wattsemi.com\/?p=26371","title":{"rendered":"PPA Optimization strategies"},"content":{"rendered":"\t\t
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ASIC Physical Design Engineers play a critical role in PPA (Power, Performance, Area) recovery<\/strong> throughout the RTL-to-GDSII flow.<\/p>\n\n

Below is a structured breakdown of their key tasks and techniques for PPA optimization, categorized by Power, Performance, and Area<\/strong>:<\/p>\n\n

\"\"<\/figure>\n
\n
    \n
  1. Dynamic Power Reduction<\/span>
    <\/strong>
    Clock Gating<\/strong>:
    <\/strong><\/li>\n<\/ol>\n

    Insert clock gating cells (ICGs) to disable clocks for idle logic blocks.
    Example<\/strong>: Automate gating with TCL scripts in synthesis\/PnR tools.<\/p>\n

      \n
    • Multi-Bit Flip-Flop (MBFF) Merging:\u00a0<\/strong>
      Combine single-bit FFs into multi-bit FFs to reduce clock network power.
      Tool<\/strong>: Synopsys DC\/ICC2\u00a0set_clock_gating_options.

      \n
        \n
      • Voltage Scaling<\/strong>:
        Implement\u00a0Multi-Vt libraries<\/strong>\u00a0(LVT for critical paths, HVT for non-critical).
        Challenge<\/strong>: Balancing timing vs. leakage power

        <\/li>\n<\/ul>\n<\/li>\n<\/ul>\n

        \u00a0 \u00a0 2. \u00a0 Leakage Power Reduction<\/strong><\/span><\/p>\n

          \n
        • Power Gating<\/strong>:
          Use\u00a0header\/footer switches<\/strong>to shut off power to idle blocks (e.g., sleep transistors). Example<\/strong>: Automated power switch insertion in Cadence Innovus.

          Body Biasing<\/strong>:
          Apply reverse body bias (RBB) to HVT cells to further reduce leakage.

          <\/li>\n<\/ul>\n

          \u00a0 \u00a03. \u00a0 \u00a0IR Drop Mitigation<\/strong><\/span><\/p>\n

            \n
          • Decoupling Capacitors<\/strong>:<\/li>\n<\/ul>\n

            Add decap cells near high-switching logic (e.g., CPU cores).
            Tool<\/strong>: RedHawk\/Voltus for decap placement analysis.

            <\/p>\n

              \n
            • Power Mesh Optimization<\/strong>:
              Increase metal width\/pitch in high-current regions.
              AWS Example<\/strong>: Graviton chips use hierarchical power grids.<\/li>\n<\/ul>\n
                <\/ul>\n
                \n

                2. Performance Optimization<\/strong><\/span><\/h3>\n\n

                A. Timing Closure<\/strong><\/h4>\n\n

                Useful Skew<\/strong>:<\/p>\n\n

                  \n
                • Deliberately imbalance clock tree latency to improve setup\/hold margins.<\/li>\n\n
                • Tool<\/strong>: PrimeTime + ECO scripts.

                  Critical Path Optimization<\/strong>:<\/li>\n\n
                • Cell Sizing<\/strong>: Upsize drivers on critical paths.<\/li>\n\n
                • Buffer Insertion<\/strong>: Break long nets to reduce RC delay.

                  Example<\/strong>:
                  tcl resize_cell -lib_cell BUF_X4 [get_cells critical_path_ff]<\/code><\/li>\n<\/ul>\n\n

                  B. Clock Tree Synthesis (CTS)<\/strong><\/h4>\n\n

                  H-Tree Structures<\/strong>:<\/p>\n\n

                    \n
                  • Balance clock skew for high-frequency designs (e.g., AWS Graviton).

                    Clock Mesh<\/strong>:<\/li>\n\n
                  • Use mesh networks for ultra-low skew in multi-GHz designs.<\/li>\n<\/ul>\n\n

                    C. Crosstalk Mitigation<\/strong><\/h4>\n\n
                      \n
                    • Shielding<\/strong>:
                      Route critical nets (clocks) between VDD\/VSS lines.
                      Tool<\/strong>: Innovus add_shield<\/code>
                      Spacing Rules<\/strong>:
                      Increase spacing for high-aggressor nets.<\/li>\n<\/ul>\n
                      \n

                      3. Area Recovery<\/strong><\/span><\/h3>\n\n

                      A. Congestion Reduction<\/strong><\/h4>\n\n
                        \n
                      • Macro Placement<\/strong>:
                        Place macros at chip edges to reduce routing congestion.
                        Example<\/strong>: Use Cadence Innovus plan_design<\/code>

                        <\/li>\n\n
                      • Cell Padding<\/strong>:
                        Add whitespace around high-density cells.<\/li>\n<\/ul>\n\n

                        B. Logic Optimization

                        <\/strong>\u00a0Library Cell Selection<\/strong><\/h4>\n\n
                          \n
                        • High-Density Libraries<\/strong>:
                          Use low-drive cells in non-critical paths.
                          Tradeoff<\/strong>: Timing vs. area.<\/li>\n<\/ul>\n
                          \n

                          4. Toolflows & Automation<\/strong><\/span><\/h3>\n\n

                          A. PPA-Aware Scripting<\/strong><\/h4>\n\n
                            \n
                          • TCL\/Python for ECOs<\/strong>:<\/li>\n<\/ul>\n\n
                              # Example: Auto-resize cells with negative slack\n\n  foreach cell [get_cells -filter \"slack < 0\"] {\n      resize_cell -lib_cell BUF_X4 $cell\n  }<\/code><\/pre>\n\n
                              \n
                            • Machine Learning<\/strong>:<\/li>\n\n
                            • Use ML-based tools (e.g., Synopsys DSO.ai) for PPA exploration.<\/li>\n<\/ul>\n\n
                              B. Signoff Correlation<\/strong><\/h4>\n\n
                                \n
                              • Cross-Tool Validation<\/strong>:<\/li>\n\n
                              • Compare power\/timing between PrimeTime (signoff) and PnR tools.<\/li>\n<\/ul>\n
                                \n
                                \"\"<\/figure>\n\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t","protected":false},"excerpt":{"rendered":"
                                ASIC Physical Design Engineers play a critical role in PPA (Power, Performance, Area) recovery throughout the RTL-to-GDSII flow. Below is a structured breakdown of their key tasks and techniques for PPA optimization, categorized by Power, Performance, and Area: Dynamic Power ReductionClock Gating: Insert clock gating cells (ICGs) to disable clocks for idle logic blocks.Example: Automate […]<\/p>\n","protected":false},"author":2,"featured_media":26373,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"postBodyCss":"","postBodyMargin":[],"postBodyPadding":[],"postBodyBackground":{"backgroundType":"classic","gradient":""},"footnotes":""},"categories":[83],"tags":[99],"class_list":["post-26371","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-rtl-to-gds2","tag-ppa"],"_links":{"self":[{"href":"https:\/\/wattsemi.com\/index.php?rest_route=\/wp\/v2\/posts\/26371","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/wattsemi.com\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/wattsemi.com\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/wattsemi.com\/index.php?rest_route=\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"https:\/\/wattsemi.com\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=26371"}],"version-history":[{"count":5,"href":"https:\/\/wattsemi.com\/index.php?rest_route=\/wp\/v2\/posts\/26371\/revisions"}],"predecessor-version":[{"id":26396,"href":"https:\/\/wattsemi.com\/index.php?rest_route=\/wp\/v2\/posts\/26371\/revisions\/26396"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/wattsemi.com\/index.php?rest_route=\/wp\/v2\/media\/26373"}],"wp:attachment":[{"href":"https:\/\/wattsemi.com\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=26371"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/wattsemi.com\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=26371"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/wattsemi.com\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=26371"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}