Virtuoso Meets Maxwell: Excluding Cells in the Schematic-Driven Flow

'Virtuoso Meets Maxwell' is a blog series aimed at exploring the capabilities and potential of Virtuoso® RF Solution and Virtuoso MultiTech. So, how does Virtuoso meet Maxwell? Now, Virtuoso platform supports RF designs, and the RF designers measure the physical and radiation effects by using Maxwell's equations. In addition to providing insights into the useful software enhancements, this series broadcasts the voices of different bloggers and experts about their knowledge and experience of various tools in the Virtuoso IC-Packaging world, along with the nuances of RF, microwave, and high-frequency designs. Watch out for our posts on Mondays.

In a complex design, a solution combining RC extraction-based method with an electromagnetic analysis to ensure a predictive simulation is required. Therefore, it is key to have an efficient partitioning methodology where the RC partition and the EM partition of the design are accurately defined.

The Virtuoso Electromagnetic Solver assistant provides a smart capability to partition the circuit without changing the golden design. Indeed, you can select hierarchically the passive instances and nets that need to be simulated with the EM solver (EMX or Clarity solvers) while the active portion of the circuit will be extracted with Quantus Extraction Solution. This is named as the schematic-driven flow.

However, the definition of the EM partition is not trivial. Strong awareness and precision is required especially for the top-level simulation where the design is very dense, and the passive instances/nets can be at any hierarchy level of the design.   

The challenge with EM model selection in the schematic-driven flow comes when there is an instance that is classified as a passive block, but it includes other instances, such as mimCap, MoMcaps, or other PDK devices, which might need to be excluded from the EM simulation.  

The mim/MoM capacitors need to be handled carefully because of the following reasons: 

• MOMcap requires a very dense mesh that will impact the whole simulation performance if the same mesh size is applied to the whole geometry
• For mimCAP, the PDK provides well-characterized models usually that can be also used to perform statistical analysis with a circuit simulator

Therefore, designers need the flexibility to include or exclude an embedded instance that is part of a passive block. This blog explains how to use the “Exclude Cell” capability in the schematic-driven flow.

Let’s take the following testcase: Instance I0 is a filter that is selected in the EM model.

The instance I0 has five terminals; therefore, five ports are expected.

However, the instance I0 is composed of Baluns, mimCAP, and internal nets.  The objective is to exclude the mimCAP instances from the EM simulation and use the PDK model for the post-layout simulation. 

The solution is the Use Exclude Cells option available in the Electromagnetic Solver assistant.

It will provide you with a list of cells from the selected Library, as shown in the following image. 

Once the excluded cells are specified, the EM Solver assistant will accurately handle the exact ports required at the extremity of the excluded cell to keep the correct connectivity in the EM extracted view generation.   

Next, the ports need to regenerate. The ports are correctly generated, as you can see in the following figure:

• Five ports for the instance I0
• Four ports for the two mimCAP instances CL and CR (two ports per instance PLUS/MINUS)

Last step is the emsolver_extracted view generation. The connectivity is as expected. The port instance is connected to the excluded mimCAP instances.

Related Resources

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Fadoua Gacim

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About Virtuoso Meets Maxwell

Virtuoso Meets Maxwell series includes posts about the next-generation die, package, and board design flow with a focus on reinventing and optimizing the design process to ensure that the designer remains a designer! Keep watching! Subscribe to receive email notifications about our latest Custom IC Design blog posts.