Virtuosity: Decoding the Mechanics of What If in Voltus-Fi-XL

‘What if?’ is a small, but powerful, question that is intended to induce profitable thoughts into a hypothetical scenario. It can, in fact, be a way to let our imagination soar and to enhance the understanding of a potential event and make it come alive. What if you were gifted with such a power to use in your power integrity tool, Voltus-Fi Custom Power Integrity Solution? In other words, what if you could foresee potential changes in your design and analyze their impact in advance? I’m sure, your life would have been easier, isn’t it?

The good news is that you get this power in Voltus-Fi Custom Power Integrity Solution XL. The ‘what-if or ECO analysis’ feature lets you analyze the impact of potential changes in the layout, also known as engineering change order (ECO) changes. You need to know about these ECO changes to fix IR drop and EM violations in the design. However, you don't have to necessarily implement these changes in the original layout and re-extract the Detailed Standard Parasitic Format (DSPF) file. You can easily analyze the impact of any potential layout changes, such as what would happen if more pins, resistors, and vias are added to certain nets, or what would the result be if a pin, resistor, or via is deleted from a net.

Although this feature has been in existence in Voltus-Fi Custom Power Integrity Solution XL for a very long time, with this post, I’m trying to call your attention to its availability and the benefits that you derive from it. 

Notable Characteristics and Benefits

The fact that the what-if analysis is an advanced debugging technique speaks for itself. Besides this, some noteworthy characteristics of the feature are as follows:

• You can run multiple incremental what-if runs. In an incremental ‘itereco’ method analysis, the simulation results from a previous, regular ‘iterated’ method EMIR analysis are reused, thereby saving you time and effort.
• Using this feature, you can modify the layout by adding or deleting pins, resistors, and vias. It lets you run design-rule checks (DRCs) and view the potential design-rule violations (DRVs) in Annotation Browser and on the layout. Thus, you can fully realize the benefits of flexibility, time saving, and more accurate final analysis, requiring lesser iterations.

Feature Mechanics

The what-if analysis feature is supported in two EMIR analysis flows: the regular ‘iterated’ method and the incremental ‘itereco’ method. The flow comprises the following steps:

1. The what-if changes or ECO commands are specified in the Voltus-Fi Custom Power Integrity Solution XL GUI, and an ECO file is generated. The ECO file is included in the EMIR control file.
2. The simulation is run with the specified what-if changes using a Spectre simulator.
3. The simulation results file is loaded in the IR/EM Results form. This file includes the information about only those nets in which the what-if changes have been applied.
4. IR/EM plots are generated as per the what-if changes made in the simulation.

Here’s a sneak peek into how the what-if analysis feature works. In the figure below, the 'delete_res' ECO command has been specified in the Voltus-Fi Custom Power Integrity Solution XL GUI. After the what-if analysis is run and the specified resistor is deleted, you can view the DRC violations in Annotation Browser.

‘What if?’ has been my all-time favorite secret question. But now that I have used the what-if analysis feature of Voltus-Fi Custom Power Integrity Solution XL, this question has been answered as far as my work related to the potential design changes is concerned. I’m sure when you use it, you'll find your answer too.

Also, if you have not already done so, I would strongly encourage you to read my last blog on the new Virtuoso EMIR analysis flow, in which I, with my two colleagues, have explained how you can run EMIR analysis with a DSPF file while staying wholly within the Virtuoso environment. 

Happy reading, and stay safe!

- Pallabi Roy 

Related Resources

For more information on Voltus-Fi Custom Power Integrity Solution, visit www.cadence.com.

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