Virtuoso Meets Maxwell: EMX—Industry-Leading EM Solver for RFICs

'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 meets Maxwell? Now, the Virtuoso platform supports RF designs, and the RF designers measure the physical and radiation effects by using the 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.

Hi all, this is my first blog for the Virtuoso Meets Maxwell series. It builds on the Virtuoso Meets Maxwell 2021 introduction blog. Today I get to discuss one of my favorite topics, electromagnetic (EM) analysis of RFICs using Cadence EMX Planar 3D Solver.

Why Do I Need Electromagnetic Simulation?

Really, it comes down to speed. We all want to go faster, right? When circuit speed increases, the old assumptions no longer work. The increase in speed equates to a decrease in wavelength and an increase in effective electrical length. This makes the electrical size of your layout become effectively larger and larger. When this happens, the assumptions of an RC or even RLCK extraction engine start to break down. True circuit performance cannot be predicted and circuit simulation will not match reality.

But This is Just for RF Circuits, Right?

Unfortunately, designers are not that lucky. Yes, traditional RF circuits, such as power amplifiers (PAs), low-noise amplifier (LNAs), and mixers need EM simulation. But, many “high-speed analog” circuits need this accuracy as well.

Let’s imagine a clock signal at 5GHz (which isn’t even that fast anymore). In order to reduce jitter, you will work to decrease the rise and fall times as much as possible. What this means is a very “square” wave. In order to accurately model this wave, many harmonics are needed. What this really means is that 5GHz is not enough; you must have an extraction that models accurately to much higher frequencies.

With your fast clock, the wavelength decreases and therefore, the electrical size of your layout becomes larger to where Kirchhoff’s current and voltage (KCL and KVL) laws will not work anymore. Depending on how tightly electrical and magnetic fields are coupled a full electromagnetic solution may be required.

What Kind of Structures can be Analyzed?

The EMX solver is a very flexible electromagnetic solver capable of characterizing nearly any passive structure. I find people think of structures as circuit components, but it is much more than that.

Certainly, the EMX solver can simulate inductors, capacitors, and resistors. It is also capable of solving larger structures as well, such as baluns and transformers. Transmission lines are also classically solved structures in the EMX solver.

Unknown to many, though, is that the EMX solver can simulate circuit blocks as well. With the use of black boxing technology, it can remove active components, properly add ports at each connection of each active component, and simulate the rest of the block. A good example of this would be simulating a VCO structure’s capacitor banks, inductor, and interconnect.

Ease of Use

The EMX Solver is the industry leader in RFIC EM analysis and it combines ease of use, performance, and foundry support. One simple form of the Electromagnetic Solver Assistant in Virtuoso Layout EXL allows you to setup sweep ranges and ports. Port structures are automatically created on your existing pin structures, making setup a snap. Once ports and frequencies are setup, the EMX solver is ready to run.

After the simulation is complete, it is simple to create S-parameter views ready for circuit simulation, data management, and sharing.

The environment even allows for easily setting up sweeps of process, temperature, and other settings. This will create multiple S-parameter models that can be swept in Virtuoso ADE Assembler.

Passive Modeling

After your structure has been modeled by the EMX solver, you may want to turn that model into a schematic-based model rather than an S-parameter file. With the Modelgen tool built into the EMX solver, this is possible for many structures.

These models accurately fit into the simulated S-parameter files and provide several advantages. You can visualize the structure and look for how improving performance could be achieved. These models are also very fast in circuit simulators. Below is an example model for an inductor:

Visualization

Baseline visualization of a structure includes simply viewing the meshing being performed. Good visualization encompasses much more than that.

With the EMX solver, we can visualize much more than this. Visualizing current in the structure as a function of phase allows for a deeper understanding of your design.

Performance

The EMX solver, by utilizing its fast multiple algorithm, is extremely fast at solving your designs. Coupling this with parallelization makes solving even large design feasible. The solver allows parallelization on one machine or across multiple machines. This allows users to take advantage of their farms to solve large circuits.

Foundry Support

Foundry support is hugely important when selecting your EM solver. The EMX solver has a huge amount of foundry support and can be used with just a process file on most foundry nodes.

The EMX solver has unique features available to support real world IC manufacturing, even at the newest of advanced nodes. Bias rules provided by the foundries allow the solver to model what will be manufactured, not just what is drawn in your layout. This is critical in terms of accuracy, especially on advance nodes. The image illustrated below is about what might be drawn versus manufactured:

Thanks for reading and happy designing!

Scott Dickinson

Related Resources

For more information on Cadence circuit design products and services, visit www.cadence.com.

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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!

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