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Case Study: Simultaneous Switching Outputs (SSOs)

This case study explores the optimization of simultaneous switching outputs (SSOs) in the RT54SX72S device, structured into four design cases: A, B, C, and D. Each case employs different methodologies for output bank separation and placement to manage delay timing during output enablement. The study analyzes worst-case scenarios for SSO mitigation, including temperature and voltage variables, while examining output enablement paths and the implications of auto-placement versus manual adjustments. The findings provide critical insights for enhancing electronic device performance through optimal layout design.

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Case Study: Simultaneous Switching Outputs (SSOs)

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  1. Case Study:Simultaneous Switching Outputs (SSOs)

  2. SSO Case Study • Device : RT54SX72S • Output Bus: 32 bits • Method: • Divided into 4 banks of 8 SSOs, each bank enabled using BUFDs for staggering • Analyzed for worst-case: • SSO mitigation (ΔT between banks for fast process and speed grade/cold/high voltage) • Setup time limitations (ΔT between first and last output enabling for slow process and speed grade/hot/low voltage)

  3. Design Schematics

  4. Design Schematics (Close-up)

  5. RT54SX72S 47 rows 126 columns

  6. Case A • All macros auto-placed by Designer • No manual adjustments to placement Outputs Enable Path

  7. Case A: Auto-placement Max ΔT Min ΔT • Minimum ΔT between banks: ~ 3 ns • Maximum ΔT between 1st and last output enabling: ~ 25 ns (average 7ns per stage)

  8. Case B • All macros initially auto-placed by Designer • Subsequently, BUFDs are placed manually to achieve significant increase in delays due to routing • Each pair of [logically] adjacent BUFDs separated by ~40 rows and ~40 columns Outputs Enable Path

  9. Max ΔT Min ΔT Case B: 40 x 40 Separation • Minimum ΔT between banks: ~ 6 ns • Maximum ΔT between 1st and last output enabling: ~ 46 ns (average 14 ns per stage)

  10. Case C • Modification of Case B with smaller separation distance between BUFDs • Each pair of [logically] adjacent BUFDs separated by ~15 rows and ~15 columns Outputs Enable Path

  11. Case C: 15 x 15 Separation Max ΔT Min ΔT • Minimum ΔT between banks: ~ 4 ns • Maximum ΔT between 1st and last output enabling: ~ 37 ns (average 8 ns per stage)

  12. Case D • All output macros are hand-placed together along one side of the die • Provides for “convenient” (seemingly optimal) board layout • All other macros are auto-placed Outputs Enable Path

  13. Case D: “Pretty” Layout Max ΔT Min ΔT • Minimum ΔT between banks: ~ 1 ns • Maximum ΔT between 1st and last output enabling: ~ 11 ns (average 4 ns per stage)

  14. Delay Summary Method Spacing Range A: Auto-placement 3 25 B: 40 x 40 Separation 6 46 C: 15 x 15 Separation 4 37 D: “Pretty” Layout 1 11

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