SIwave Far field simulation

I want to do EMI EMC analysis on my PCB of a ZCS buck converter. I am using SIWave for this. When I have to select current and voltage sources do I have to mention all the components using the voltage (say +18V) as a voltage source or just the pin header that is supplying it? Let's say I have a 18 V to 5 V regulator ic. What should I assign this IC as? Also, does PWM generator ic like TI's SG3524 be assigned a current source?

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  • mannymanny Forum Coordinator
    edited October 21

    I'm going to provide a high-level answer to your question that should get you up and running. First off this is an advanced simulation that you are after. The workflow for conducted emissions analysis of a buck converter is to start with SIwave, export to Q3D, build the circuit, run the analysis and view the emissions results. In SIwave, set up pin groups from the components under ICs and I/Os. Assign Sources/Sinks. The sink/source assignments can be done on the Export to Q3D dialog. In general, power consuming active devices are set to current sinks. VRMs are set to voltage sources. The export to Q3D generates a broadband model. Now set up a circuit simulation where you can assign SPICE/IBIS models or generic sources and generate the waveform. Good luck with your simulation!

  • Hello @manny , thank you for your response. I have many doubts, but I'll ask a few first. I thought conducted and radiated emissions were the Near and Far field solvers in SIwave. It appears not from your answer, so what are those for? When you say "pin groups", do you mean this : Say I have a PWM IC SG3524 on my board. So from the create pin groups option I choose the corresponding RefDes and "select all nets" and then hit "create pin groups" ? I am not clear about the purpose of this, I think it is to have a better analysis once I have assigned current and voltage sources.

    Also, could you suggest/tell me what kind of a "circuit" have I got to set up for EMI analysis? Do you mean something like the LISN model? Sorry if this question sounds trivial, I have just begun venturing in this domain !

    Thank you, your answer has been very helpful.

  • mannymanny Forum Coordinator

    As I mentioned to you before this is an advanced simulation. No, this is not a trivial question :) You're absolutely right - you'll need to use the LISN model in your circuit design.

    You are right about the pin groups. Assume you select an I/O device such as a controller. Selecting the controller from the Components tree in SIwave will select all the associated pins. Use the "Create/Manage Pin Groups..." under the Tools menu. Choose the part name and all the ref designators. And select all nets and create Pin Group(s).

  • @manny Your comments have been really helpful, it is starting to make some sense to me. I've proceeded a bit since then, and I have some questions:-

    1) When I simulate any solver, (I started off with the simplest (seemingly?) DC IR drop analysis,) I get "Capacitors ignored, Inductors ignored resistors ignored" messages. How do I correct this? Is this because it cannot map the capacitors etc. to the actual models?

    2) Can I put any of the current sinks' GND terminal as the Ideal Ground Node (0V) which comes up just before simulating DC IR?

    3) When I try to compute resonant modes for my 2-layer PCB of a soft-switching buck converter, I get an error "Could not compute resonant mode voltage plots. Could not locate requested layer pair in mesh file". Then I checked my layer stack up and I found that it shows the elevation of the bottom layer = 0mm. I suspect this is why I cannot get the voltage differences between top and bottom layers. How do I correct this? Is it more to do with my PCB design than in SIwave?

    4) Are Header pins also supposed to be assigned a voltage source apart from regulator ICs?

    Thank you very much.

  • mannymanny Forum Coordinator

    1) The passive devices are not attached to the nets that you are simulating in your DCIR analysis so SIwave generates warnings. These are nothing to worry about. I'll get back to your other questions later.

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