Virtuoso Studio: Am I Right? Parasitic Extraction Viewpoint

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In today's fast-paced world, parasitic extraction has become a pervasive issue. This phenomenon isn't just biological – it also extends into our System-On-Chip (SoC) design. With the rise of sophisticated technologies, an intricate web of devices connects our world—each one smarter, smaller, and more efficient than the last. This technological marvel has been largely fueled by innovations in SoC developments. Reliable, efficient, and multifunctional SoCs are the heart of these devices, but new challenges arise as they shrink to fit more functionality into them. Among these, Electromigration (EM) and IR drop are crucial from a layout completion perspective because these challenges may impact the longevity and functionality of the design. Traditionally, we extract the EM and IR details post-layout completion, which may create delays in the design. Imagine a scenario where you can see the EM and IR details on the fly during layout design! Wouldn’t that make life easier for layout designers?

In this post, we'll explore the importance of in-design parasitic extraction in the face of these issues and how it shapes the lifecycle of modern SoC layouts, ensuring they meet the stringent requirements for functionality and reliability. Let’s dive into the microscopic world where the battle for durability in the face of EM and IR drop is fought and won.

Anatomy of a SoC Challenge: The Predicament of EMIR

With shrinking geometries of SoCs, there are two things to worry about: EM and IR drop. EM is when electrons move through metal, dragging metal ions toward the current. The miniaturization of system-on-chips (SoCs) alters the dimensions of the interconnecting wires within these components. As the wires become longer and narrower, an issue arises: narrow wire "necks" can result in increased current density. This heightened current can exert force on the metal atoms at the constricted point, further constricting the already narrow passage. This self-propagating issue is exacerbated at higher temperatures, presenting a menace to sectors like the military and automotive industries where operational conditions can be taxing. IR drop is another thing to be cautious about. It can cause the voltage to drop below the spec voltage for the cells, leading to intermittent failures. For designs where blocks are powered down, it's crucial to analyze the voltage to ensure it doesn't sag so much that other parts of the chip malfunction when a block is reactivated.

Post-Construction Correctness Check

As we examine the complexities of constructing precise interconnects, the importance of post-construction analysis becomes evident. Ensuring the accuracy of current distribution post construction phase is critical to prevent issues arising from static or limited current considerations during the design process. Traditionally performed post-layout completion, the parasitic extraction process can lead to delays—from minor adjustments to comprehensive redesigns—if modifications are deemed necessary. A proactive and dynamic strategy is indispensable to avoid this bottleneck and meet the reduced time windows. Such a strategy minimizes repetitive parasitic extraction and anticipates major revisions, guaranteeing the interconnect accuracy and reliability while avoiding prolonged design cycles.

Parasitic Extraction: The Crusade Against Parasitics

Parasitic extraction is paramount in the layout life cycle, ensuring adherence to stringent specifications and enhancing the precision of the layout. Accurately accounting for these parasitics is instrumental in refining circuit simulations and bolstering the dependability of the simulation output. To engineer a robust and enduring SoC, it is imperative to conduct thorough EMIR checks. This ensures that every physical design component is electrically sound from inception and finely tuned to fulfill the original design intentions. Moreover, verifying the integrity of interconnects as correct-by-construction is vital for long-term reliability. Each manufacturing process is governed by intricate rules determining the allowable current in each layer and associated vias. This can vary for currents flowing in opposite directions, and layout engineers may need to engage in rigorous scrutiny and perform iterative simulations and correction to comply with the process regulations related to current capacity per layer and via.

This is particularly true for the more intricate advanced nodes, which offer considerable rewards but pose substantial risks. The uncertainty materializes when circuit designers wait for a fully composed LVS DRC clean layout before validation against the original design intent is possible. During this latency, numerous layout decisions regarding component placement and routing occur without considering their electrical ramifications. It's only during the verification phase—post-parasitic extraction and simulation—that the repercussions of these decisions emerge. Consequently, design teams find themselves in protracted cycles of iteration between verification and implementation to achieve the intended design, an exercise in diminishing productivity.

What if we could get immediate feedback on how a layout feature or change impacts electrical design requirements like EM – as you draw the layout? Or discover parasitic issues on the interconnect instead of waiting for post-layout extraction? Any extraction-related call for design adjustments has the potential to significantly disrupt the schedule, potentially escalating from minor modifications to extensive overhauls.

The Proactive Approach: Interactive Simulation and Dynamic Checks

Therefore, the call to arms is a dynamic approach to nip potential disasters in the bud, and modern tools like Cadence Virtuoso Studio are leading the charge with interactive simulation-driven routing and Electrically Aware Design (EAD) flow.

Virtuoso Simulation-Driven Routing: The Early Warning System

Simulation-driven routing allows designers to peek into compliance with simulated datasets, identifying EM and parasitic troubles early in the design process. Virtuoso simulation-driven routing is a step towards “correct by construction” routing driven by electrical requirements. It provides an environment to consider the current density and maximum resistance design rules during the interactive routing. This foresight is critical for industries where reliability over long periods—like in automotive or aeronautics—is non-negotiable. Featuring a unique in-design solution, interactive Virtuoso simulation-driven routing provides a powerful new way for a layout designer to have a predictable flow to meet the current density constraints and, in turn, significantly reduces the sign-off time and improves productivity and design reliability. Not only does interactive simulation-driven routing empower layout engineers to adhere to project timelines with the help of interactive routing, but also it helps layout engineers:

• Visualize the current distribution per net.
• Control simulation-driven routing to calculate the current according to the net topology.
• Auto-size wires and vias according to the estimated current.
• Auto-connect devices according to the estimated current.
• Fix EM Violations using the EAD browser.
• Reduce the number of iterations and improve the layout productivity by up to 50 percent. 

Virtuoso EAD Flow: Visualizing Challenges As They Happen

The EAD flow extends beyond mere checks—it's about capturing and visualizing RC parasitics live, during layout edits, and fixing violations on the spot. With the Cadence Virtuoso Studio Electrically Aware Design (EAD), you can get immediate feedback on how changes affect your layout and circuit performance. This technology not only allows for instantaneous EM checking but also enables parasitic re-simulation. Designers can now re-simulate any segment of the layout—from the earliest crucial net to the finalization—confirming adherence to original design specifications. These advancements collectively enhance efficiency and empower designers to fine-tune and optimize layouts during the design process for peak performance. Early adopters of EAD report a potential reduction in total design time of at least 30 percent, significantly cutting down the costly iterative loops between implementation and verification stages. It's about reshaping the paradigm from reactive correction to proactive protection.

Conclusion

The realm of SoC designs constantly evolves, with shrinking sizes presenting formidable foes like EM and IR drop. However, with contemporary methods like Virtuoso simulation-driven routing and EAD, parasitic extraction engineers are better equipped than ever. The real-time results enable designers to make high-quality layouts while ensuring their creations withstand the tests of time and performance.

Related Resources

• Virtuoso Studio
• What is Simulation Driven Routing (SDR)?
• Virtuoso Electrically aware design design guide

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