I'm trying to remove noise from a SMPS 5V supply. You can see a 'scope view of the noise (two 'groups' of noise present) in the two attached images. The built in low-pass filter on the 'scope can dramatically smoothen the noise when set with 25Mhz as the cutoff frequency, and I'm trying to emulate this filtering with simple components on a board (see attached breadboard image which features DC power input, 100uF decoupling capacitor, and RF lowpass filter from 220ohm resistor and 68pF capacitor -> cutoff of 10.6Mhz).
So far, I have not been able to significantly attenuate the noise at all. I've tried low and high cutoff frequencies with simple 1-pole RC (many different resistor/cap combos) and 1-pole LC filters (I only have a 100uH coil, but many different caps). I've also tried many many different power rail decoupling capacitors, ranging from a few pFs to bulkier electrolytes.
Trivial circuit diagrams:
- RC: http://en.wikipedia.org/wiki/File:RC_Series_Filter_(with_V%26I_Labels).svg
- LC: http://www.ampbooks.com/home/amplifier-calculators/LC-ripple-filter/LC-lowpass.gif
Nothing is shaking the noise.
Any ideas what I'm doing wrong, or ideas of other things to try?