SIwave far field simulation results

I am trying to use ANSYS SIwave for EMI/EMC testing of my PCB. I have the following questions which don't seem to be covered in the tutorials: -

1) Suppose I am working with +5V, +12 V and +18 V on my board which are supplied through pin headers. And I have 2 components which use the +12 V say - a voltage regulator and a PWM IC VCC supply. Do I have to keep the pin header and regulator BOTH as a voltage source and PWM IC as a current source?

2) When I make a far-field computation using the Far Field simulation tool, it gives me several results. What is the Y axis representing in this plot?

dB(MaxETotal)? Why is it dB? My sweep range is 150kHz to 30MHz.


  • I need this a bit urgently, it is for a project I'm working on so any points in the right direction would help too.

  • mannymanny Forum Coordinator
    edited October 14

    Hello! Thanks for your questions. Please see my answers below.

    1.) It appears to me that you're trying to run a DCIR simulation and that being the case, your settings seem reasonable. PWM IC consumes power so you can define a current sink to it. We have complete end to end DCIR workflow videos right from reading the schematic of a board. Watch Part 1 and Part 2 - all the configuration steps are covered. These videos will give you a clear idea of where and how to define voltage sources and current sinks on a PCB before running a DCIR simulation in SIwave.

    2.) At each frequency, SIwave plots the max value of Etotal. It is plotted in decibels since it distributes the points logarithmically allowing for a smaller set of values of Etotal and a smoother curve to be displayed on the graph. You can, however, set this to any appropriate Function such as mag or dB. To do this, navigate to the project manager window in Electronics Desktop and just double-click the report option. This operation will open the Reporter dialog. From here, you can select the "Function" of interest instead of dB.

  • mannymanny Forum Coordinator
    edited October 14

    Finally, since you are doing a EMI/EMC testing of your PCB, you may want to consider doing DRCs in SIwave - use the EMI Scanner and the subsequent EMI Xplorer capabilities to identify areas of potential interference on PCB prior to simulation. With Xplorer you can further study the shades of gray in the violations.

  • @manny I'm using SIwave version 17.2, I don't see EMI Xplorer or EMI Scanner in this. I think I have to upgrade to the newer version for this. Also, could you explain with respect to the graph that I've posted here its meaning, that will help me realize if it is something totally wrong. I had thought that Far field results meant radiated emissions, and it may be that I'm wrong. So it would help if I were pointed in the right direction.

  • mannymanny Forum Coordinator
    edited October 29

    1.) Yes, EMI Scanner and Xplorer capabilities are available in later versions of SIwave such as 2019 R2 and higher.

    2.) To an extent you are right. Consider an example of a net transitioning from a layer through a via to a bottom layer and continuing along. Let's say the net is referencing power and ground planes respectively on the upper and lower layers and assume that caps are missing in this region. The caps here are supposed to ensure a continuous return path for the current. A far field simulation can give you a plot depicting a picture of the impact of plane resonance on the maximum radiated electric field. So, decoupling caps can be added to alleviate this radiated emissions issue - the caps can be added between power and ground planes. Adding these decoupling caps can shift the resonance and suppress the far field peaks and reduce the associated electric field.

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