Tip to figure out noise problems in a pcb.

[flote21]

Hello people. I am very frustrated right now. I designed a PCB to convert the anaolg signal provided by a image sensor into digital impulses.
In my first revision of the board I made several mistakes in Altium (I place the footprints mirrored) but in the end, I was able to run the board without too much problems and it is working properly. But now I made a new revision of my PCB and little swing in the image is displayed when the sensor is running. it is like a electric noise generated in the pcb but I cant figure out where it is the origin...because the new rev the same layout and the same components that the previous revision. The only change that I did was place the components in the right way (no mirrored). Any tip to figure out the origin of noise problems?

Thanks

 

[andre_luis]

...I made a new revision of my PCB and little swing in the image is displayed when the sensor is running. it is like a electric noise generated in the pcb but I cant figure out where it is the origin...Thanks

Based on observed behavior of such noise compared to the known horizontal video scan rate, can you determine what is its dominant frequency ?

This way, you can take the focus on the right direction to find the cause of failure.



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[flote21]

That it is my problem. I cant know wich is the freq of the swing.... I think that the origin of my noise can be the ADC. I observed that there is a input in the ADC which is very sesnsible to the noise. It is the ref voltage. To filter out this ref volt i placed a R-C filter in the pin of the ADC (100ohm and 10uF). After several tests, I discovered that if I change the vallue of the R in the filter R-C the swing is bigger. But The vaule with less swing is 100 ohm. The previos version of my design has also the same value of R and there is not swing...IT is very strange..