2

I will be soon testing a product to an electric field spectrum requirement (i.e. in the 100's of dBµV/m vs MHz), and it shouldn't be a problem because of how small the values are compared to the testing levels of other products I've made - however, it's bothering me that I seem to miss something about how these emissions couple with our circuits.

I'd like to be able to calculate a very rough voltage disturbance value for simple subcircuits. I know it's much more complex than what a simple formula can cover, but I am ready to make large simplifications and assumptions to get ballpark/rough order of magnitude values while grasping the various mechanisms at play.

Let's assume the following victim circuit.

schematic

simulate this circuit – Schematic created using CircuitLab

For a X Volts/meter requirement, does that mean X times d will be applied between VM1 and VM2, and X times h between each VM and GND? (or rather, VM should probably be at the middle of RT) If so, with what series resistance?

By the way, I know these traces would also be capacitively coupled, and I'm not talking about this - purely the external disturbance.

Mister Mystère
  • 9,477
  • 6
  • 51
  • 82
  • 2
    IMHO the model you wish to apply is too simplified and hence not going to describe the disturbances you're after. Thinking of one your circuit elements, say RT, electric field can be written in two conflicting ways, (VM1-VM2)/d or X (assuming field/resistor physical parallelism). Now which is true? Generally none, external field X will be locally changed by VM1 and VM2 and at the same time VM1 and VM2 will be changed by the external field. So, all in all, the stray capacitances you were trying to avoid are simply a way to model those fields interactions, not a different phenomenon. – carloc Jul 08 '23 at 08:10
  • Your question is unclear: 1. you show two circuits but label them as one ("victim circuit"); 2. field strength is, well, a field: you are using the wrong kind of diagrams to describe your system; schematics have no awareness of fields. Please provide an example layout and aggressor-victim geometry. Preferably also provide which standard(s) you will be testing to. 3. Capacitors operate on electric fields; such interference couples capacitively; you're asking for series resistance, so it isn't clear if this is a matter of confusion, or if there is something else you are asking for. – Tim Williams Jul 11 '23 at 11:00
  • @TimWilliams: I voluntarily want this question to be non-specific. I only added typical circuits for inspiration of potential answers - or to enable the more convenient use of component names in their answer if they so wished, but a layout including victim setup would have actually steered people in the wrong direction because to get it on point, I would need to have understanding that I am actually requesting here. Since you seem to be able to answer, would you mind answering completing the gaps of the example, or using another one? – Mister Mystère Jul 13 '23 at 16:28
  • 1
    Hmm. A general question is alright, but keep in mind the scope of a general answer grows exponentially, and so the chance of an answer (or a complete one..) shrinks exponentially as well. But I'm not even clear what you're asking; can you address some of the points? You also mention "susceptibility" and "emissions": Whose emissions? What susceptibility? Is this a self-interference thing (two nets on a PCB) or is there an external antenna, and if so, what type / standard? – Tim Williams Jul 13 '23 at 16:41
  • I intend the title to take precedence on any conflict with the body of the question, so it's the case of the susceptibility of a circuit to an external electric field - which I assume would be emitted by other equipment, but it's out of the scope of the question. I only have a field value, so I assume a test house would calibrate the distance and emissions of the antenna so that the circuit experiences that field locally. – Mister Mystère Jul 14 '23 at 05:29
  • I'd be glad to give you the bounty too though bear in mind it expires in the next 11h – Mister Mystère Jul 14 '23 at 18:09

0 Answers0