The spectrum plot raises doubts, that the shown voltage level is actually generated from the SMPS, because effectively no discrete lines are visible. It looks rather like amplifier noise or another kind of measurement artefacts. Thus the measurement seems unsuitable to determine a filter dimensioning.
P.S.: Also the shown numbers for interference levels sound unreasonable considering the given circuit. Apparently, the probed voltage is almost unaffected by the LC filters. This isn't a problem of filter dimensioning rather than probe connection or possibly circuit ground layout.
1.What is the frequency of switching and let say we confined ourselves to use a second order LC filter. H(s)=1/(1+(s/wo)^2) in which W0=1/sqrt(LC). Assume that the switching frequency is much further that wo. then the rejection of it can be found by :
P.S.: Also the shown numbers for interference levels sound unreasonable considering the given circuit. Apparently, the probed voltage is almost unaffected by the LC filters. This isn't a problem of filter dimensioning rather than probe connection or possibly circuit ground layout.
I think, the "noise" level measured after the voltage regulator doesn't show a signal that is propagated through the filter and regulator. I assume, that it either shows a measurement artefact (e.g. due to incorrect probe grounding) or interferences that bypass the filter, because the circuit layout is unsuitable.could you explain me the details
.As you see by it's AC gain, after 1MHz, the regulator hardly can diminish the high frequency noises
As I noted, I measure near ground pad with below 1 inch(maybe below 10mm), The result is 3mV. Could I trust measuring result. Is that not negligible?To determine the probe interference level, you may want to measure the voltage between two adjacent ground pads with the same method. If it's neglectable, you can trust the measurements.
Sorry, I missed the respective explanation in your previous post. Yes, I think 3 mV is acceptable. The interference spreading mechanism in your circuit is still unclear to me.Could I trust measuring result. Is that not negligible?
Please kindly explain me about what interference spreading mechanism means.The interference spreading mechanism in your circuit is still unclear to me
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