Hi, I have a design that I have some EMI issues with, so I'm trying to reduce the EMI with chip ferrite beads. Here are a couple of places I'm thinking of putting them, but I'm not sure if they're suitable or what kind of chip beads to use(impedance rating mostly).
- Power and GND signals coming from the 2 connectors. Thinking of putting some chip beads on these to prevent any noise coming in or going out of the cables.
- USB DP/DM signals. Thinking of putting a common mode filter here as per USB specifications.
- I have a membrane keypad connected to the main board with a FPC connector. It has button signals, LED signals and a power signal. It seems to be acting like an antenna from my near field probe tests. Putting a metal plate(or even aluminum foil) under it significantly reduces emission, but my casing is plastic. Pasting aluminum tape on the other side of the plastic doesn't seem to help much. I'm thinking of putting chip beads on all the signals, but I'm not sure if it'll help, or what kind to use. The signals are all very low frequency(human keypad input) with the exception of 1 of the LEDs which is activity. I'm wondering if I can just use the highest impedance chip bead arrays I can find, since it's a very low speed signal that's almost DC.
- I have a daughterboard that's connected with a 2x22 IDE type header that transfers IDE signals. It has its own power/gnd plane like the main board, via the power/gnd pins. This seems to leak quite a bit of radiation, but I'm not sure how to reduce it. Since this is a high speed signal, I'm wondering if it's feasible to put in 44 chip beads in there. The signals are already properly terminated with resistors as per reference design.
Thanks!