How to reduce the noise in PCB design

[arizona999]

Hi,

I am designing a current source with a noise value less then 5uA rms. When I measure the noise in this current source, I found that there are noise from AC/DC bridge rectifier at the frequency of 120Hz and the radiation from the fluorescent lamp.

I just wonder is there any good way to reduce the EMI from the fluorescent lamp?

Thanks.

 

[andy1]

I think you need to describe a little bit more in detail what your current source looks like. "Current source" is too general a term that can mean anything.

The noise you saw may have come from a voltage supply stage which may require a lot of filtering using a combination of chokes, and good caps as noise filters.

Make sure you have very good ground on your power supply which eliminate ground bounce and prevent noise from passing through all those power supply filters. Try using star grounding which eliminate most of gournd loop which affects sensitive analog circuits.

You could use shielding on your current source if possible. Ground the shield. But I am not sure how effective shielding will works at 120Hz signal. Maybe someone else will comment on that.

But again, the power supply stage is very important and see if you could clean up the noise from there

 

[vfone]

Here you have some applications how to implement EMI filters. Is not an easy task, but not impossible to do.
**broken link removed**
You can by or request samples of EMI filters from Murata. Also they have a nice and free EMI filter selection simulator.
**broken link removed**

 

[markty]

Add more capacitor at the bridge rectifier output to
reduce the noise.