Filter desing for EMI frequance

[rsklan]

Hi everyone,

I am conducting EMI/EMC investigations on my PCB. I observed the noise levels and noticed a few things. For example, EMI noise is being generated by the inductor in the converter structure. This occurs at around 900 kHz. I have detected this, and I want to design a filter for it. In such cases, how should a filter be designed? For example, I have several noise sources, and I know their frequency values. What should I consider when designing a filter in this scenario?

 

[barry]

Radiated? Conducted? What do you want to filter, input to an opamp? Output connector? Power supply rail? This is too general a question to answer.

 

[rsklan]

Here's the translation of what you wrote:

---

I am just looking for general guidance on how to approach this kind of problem. For example, I have a motor driver H-bridge circuit, and I am unable to read the current through the ADC. From an EMI perspective, I used a near-field probe and detected noise between 900kHz and 2MHz. Later, I performed an EMI test and observed peaks at these frequencies. This is just a scenario. In such cases, what general approach should I take to move forward?

 

[barry]

Again, you don't provide any useful information. All I can infer is:
1) You've got some radiated EMI.
2) You're ADC is not working.

I see no correlation. Are you seeing the radiated frequencies in your ADC readings? Just saying "I am unable to read the current" tells us nothing about your problem. This is like saying "There's a bright light outside my window. My bicycle doesn't work."

There are LOTS of ways of mitigating EMI problems: fixing the problem at the source; adding a filter on inputs; shielding. Without information it's impossible to answer.