{"id":26280,"date":"2025-05-20T21:27:10","date_gmt":"2025-05-20T21:27:10","guid":{"rendered":"https:\/\/wattsemi.com\/?p=26280"},"modified":"2025-05-21T04:59:30","modified_gmt":"2025-05-21T04:59:30","slug":"low-power-power-reduction-techniques-to-help-close-ir-drop","status":"publish","type":"post","link":"https:\/\/wattsemi.com\/?p=26280","title":{"rendered":"Power reduction hacks for better PPA"},"content":{"rendered":"\n

In ASIC Physical Design, mitigating IR drop (voltage drop due to resistance in power delivery networks) is critical for power integrity. Here are key power reduction methods used for achieving a better PPA and to help close on the IR drop limits, along with practical implementations:<\/strong><\/p>\n\n\n\n

\n\n\n\n

1. Power Grid Optimization<\/strong><\/h3>\n\n\n\n

A. Mesh Density Enhancement<\/strong><\/h4>\n\n\n\n
    \n
  • Technique<\/strong>: Increase width\/spacing<\/strong> of power rails and straps.<\/li>\n\n\n\n
  • Impact<\/strong>: Reduces resistance ((R = \\rho \\cdot L\/A)) in high-current regions.<\/li>\n\n\n\n
  • Tool Command (Cadence Innovus)<\/strong>:<\/li>\n<\/ul>\n\n\n\n
      set_power_ring_strategy -nets {VDD VSS} -width 2um -spacing 1um<\/code><\/pre>\n\n\n\n
    B. Decoupling Capacitors (Decaps)<\/strong><\/h4>\n\n\n\n
      \n
    • Technique<\/strong>: Place decaps near high-switching logic (e.g., clock buffers, ALUs).<\/li>\n\n\n\n
    • Impact<\/strong>: Local charge reservoirs suppress transient IR drop.<\/li>\n\n\n\n
    • Implementation<\/strong>:<\/li>\n<\/ul>\n\n\n\n
        add_decaps -cell DECAP_1UM -density 5% -region {x1 y1 x2 y2}\n<\/code><\/pre>\n\n\n\n
      \"\"<\/figure>\n\n\n\n
      \n\n\n\n
      <\/p>\n\n\n\n
      2. Clock Domain Optimization<\/strong><\/h3>\n\n\n\n
      A. Clock Gating<\/strong><\/h4>\n\n\n\n
        \n
      • Technique<\/strong>: Disable clock trees for idle logic blocks.<\/li>\n\n\n\n
      • Impact<\/strong>: Reduces dynamic power (switching activity) \u2192 lowers peak current.<\/li>\n\n\n\n
      • Example<\/strong>:<\/li>\n<\/ul>\n\n\n\n
          insert_clock_gating -gate_type ICG -threshold 10<\/code><\/pre>\n\n\n\n
        \"\"<\/figure>\n\n\n\n
        B. Multi-Bit Flip-Flop (MBFF) Merging<\/strong><\/h4>\n\n\n\n
          \n
        • Technique<\/strong>: Combine single-bit FFs into multi-bit FFs.<\/li>\n\n\n\n
        • Impact<\/strong>: Fewer clock buffers \u2192 lower clock network power.<\/li>\n\n\n\n
        • Tool Command<\/strong>:<\/li>\n<\/ul>\n\n\n\n
            set_optimize_registers -merge_flops true<\/code><\/pre>\n\n\n\n
          \"\"<\/figure>\n\n\n\n
          \n\n\n\n
          3. Logic & Placement Strategies<\/strong><\/h3>\n\n\n\n
          A. Voltage Scaling<\/strong><\/h4>\n\n\n\n
            \n
          • Technique<\/strong>: Use Multi-Vt libraries<\/strong>:<\/li>\n\n\n\n
          • LVT<\/strong> (Low-Vt) for critical paths.<\/li>\n\n\n\n
          • HVT<\/strong> (High-Vt) for non-critical paths to reduce leakage.<\/li>\n\n\n\n
          • Impact<\/strong>: Balances performance and IR drop.<\/li>\n\n\n\n
          • Command<\/strong>:<\/li>\n<\/ul>\n\n\n\n
              set_leakage_optimization true -power_driven true<\/strong><\/code><\/pre>\n\n\n\n
            B. Dynamic Voltage Frequency Scaling (DVFS)<\/strong><\/h4>\n\n\n\n
              \n
            • Technique<\/strong>: Adjust voltage\/frequency based on workload.<\/li>\n\n\n\n
            • Impact<\/strong>: Lowers average current demand.<\/li>\n\n\n\n
            • Implementation<\/strong>: Requires power switches<\/strong> and adaptive clocking.<\/li>\n<\/ul>\n\n\n\n
              \n\n\n\n
              4. Routing & Signal Integrity<\/strong><\/h3>\n\n\n\n
              A. Shielding High-Speed Nets<\/strong><\/h4>\n\n\n\n
                \n
              • Technique<\/strong>: Route critical nets (clocks) between VDD\/VSS.<\/li>\n\n\n\n
              • Impact<\/strong>: Reduces crosstalk-induced current spikes.<\/li>\n\n\n\n
              • Command<\/strong>:<\/li>\n<\/ul>\n\n\n\n
                  shield_net -net CLK -shield_net VSS -width 0.5um<\/code><\/pre>\n\n\n\n
                B. Staggered Buffer Insertion<\/strong><\/h4>\n\n\n\n
                  \n
                • Technique<\/strong>: Insert buffers in staggered phases.<\/li>\n\n\n\n
                • Impact<\/strong>: Smoothes di\/dt (current slew rate) to avoid IR spikes.<\/li>\n\n\n\n
                • Example<\/strong>:<\/li>\n<\/ul>\n\n\n\n
                    set_buffer_opt_strategy -stagger_insertion true<\/code><\/pre>\n\n\n\n
                  \n\n\n\n
                  5. Advanced Techniques<\/strong><\/h3>\n\n\n\n
                  A. Power Gating<\/strong><\/h4>\n\n\n\n
                    \n
                  • Technique<\/strong>: Use header\/footer switches<\/strong> to shut off power to idle blocks.<\/li>\n\n\n\n
                  • Impact<\/strong>: Eliminates leakage but requires wake-up time.<\/li>\n\n\n\n
                  • Implementation<\/strong>:<\/li>\n<\/ul>\n\n\n\n
                      insert_power_switch -name PSW -control_signal SLEEP -header<\/code><\/pre>\n\n\n\n
                    \"\"<\/figure>\n\n\n\n
                    B. TSV Redundancy (3D ICs)<\/strong><\/h4>\n\n\n\n
                      \n
                    • Technique<\/strong>: Add redundant Through-Silicon Vias (TSVs)<\/strong>.<\/li>\n\n\n\n
                    • Impact<\/strong>: Reduces resistance in vertical power delivery.<\/li>\n\n\n\n
                    • Analysis<\/strong>:<\/li>\n<\/ul>\n\n\n\n
                        analyze_3dic_power -tsv_resistance 0.01 -tier 2<\/code><\/pre>\n\n\n\n
                      \n\n\n\n
                      6. IR-Aware Timing Closure<\/strong><\/h3>\n\n\n\n
                      A. Voltage-Aware STA<\/strong><\/h4>\n\n\n\n
                        \n
                      • Technique<\/strong>: Use PrimeTime-SI<\/strong> with voltage derating.<\/li>\n\n\n\n
                      • Impact<\/strong>: Accounts for IR drop in timing signoff.<\/li>\n\n\n\n
                      • Command<\/strong>:<\/li>\n<\/ul>\n\n\n\n
                          set_voltage_derate -drop 0.9V -corner worst<\/code><\/pre>\n\n\n\n
                        B. ECO Fixes<\/strong><\/h4>\n\n\n\n
                          \n
                        • Technique<\/strong>: Resize cells or add buffers in IR-drop hotspots.<\/li>\n\n\n\n
                        • Example<\/strong>:<\/li>\n<\/ul>\n\n\n\n
                            eco_add_buffer -cell BUF_X2 -location {x y} -net VDD<\/code><\/pre>\n\n\n\n
                          \n\n\n\n
                          7. Toolflow for IR Closure<\/strong><\/h3>\n\n\n\n
                          A. RedHawk\/Voltus Analysis<\/strong><\/h4>\n\n\n\n
                          # Ansys RedHawk\nredhawk_analyze -ir_drop -dynamic -scenario worst_case<\/code><\/pre>\n\n\n\n
                          B. Power-Aware Place & Route<\/strong><\/h4>\n\n\n\n
                          # Cadence Innovus\nset_power_opt_mode -place true -route true<\/code><\/pre>\n\n\n\n
                          \n\n\n\n
                          \"\"<\/figure>\n\n\n\n
                          Key Takeaways<\/strong><\/h3>\n\n\n\n
                            \n
                          1. Preventive Measures<\/strong>: Optimize power grid and decap early.<\/li>\n\n\n\n
                          2. Dynamic Reduction<\/strong>: Clock gating, MBFF merging.<\/li>\n\n\n\n
                          3. Signoff Correlation<\/strong>: Voltage-aware STA and EM checks.<\/li>\n<\/ol>\n\n\n\n
                            Example Interview Q&A<\/strong>:
                            Q<\/strong>: “How would you fix IR drop in a CPU block?”<\/em>
                            A<\/strong>:<\/p>\n\n\n\n
                            \n
                            “First, I\u2019d analyze RedHawk reports to identify hotspots. For localized drop, I\u2019d add decaps and widen power straps. For global drop, I\u2019d implement clock gating and use HVT cells in non-critical paths. Finally, I\u2019d validate with voltage-aware STA.”<\/em><\/p>\n<\/blockquote>\n\n\n\n
                            \"\"<\/figure>\n","protected":false},"excerpt":{"rendered":"
                            In ASIC Physical Design, mitigating IR drop (voltage drop due to resistance in power delivery networks) is critical for power integrity. Here are key power reduction methods used for achieving a better PPA and to help close on the IR drop limits, along with practical implementations: 1. Power Grid Optimization A. Mesh Density Enhancement B. […]<\/p>\n","protected":false},"author":2,"featured_media":26285,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"postBodyCss":"","postBodyMargin":[],"postBodyPadding":[],"postBodyBackground":{"backgroundType":"classic","gradient":""},"footnotes":""},"categories":[84,40],"tags":[56,55,86],"class_list":["post-26280","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-pdn","category-technology","tag-clock-gating","tag-power-gating","tag-power-reduction"],"_links":{"self":[{"href":"https:\/\/wattsemi.com\/index.php?rest_route=\/wp\/v2\/posts\/26280","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=26280"}],"version-history":[{"count":5,"href":"https:\/\/wattsemi.com\/index.php?rest_route=\/wp\/v2\/posts\/26280\/revisions"}],"predecessor-version":[{"id":26309,"href":"https:\/\/wattsemi.com\/index.php?rest_route=\/wp\/v2\/posts\/26280\/revisions\/26309"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/wattsemi.com\/index.php?rest_route=\/wp\/v2\/media\/26285"}],"wp:attachment":[{"href":"https:\/\/wattsemi.com\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=26280"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/wattsemi.com\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=26280"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/wattsemi.com\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=26280"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}