> I use a oscillscope to observe the VCC and GND respect to the same > GND.=20 If you are seeing noise on GND with respect to itself (i.e., you short out the scope probe leads and attach their common point to a GND), then you have a measurement problem. Either the probe wires are too long and other noise is being induced into them (you have a current loop, useful for probing for magnetic fields), or there is a "common-mode" kind of problem through the scope. For the former, shorten up your probe wires to the bare minimum, and keep them close together. For the latter, try plugging the scope into a different outlet, preferably the same AC power source as the customer equipment under test, or try an isolation transformer, or try a different model scope and/or probes. Differential probes might help too. Until you resolve this measurement problem you can't rely on anything your scope tells you about noise. You should be measuring zero, but the scope is showing you 500mV that isn't there. ------------------------------------------------------------------ To unsubscribe from si-list: si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field or to administer your membership from a web page, go to: //www.freelists.org/webpage/si-list For help: si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field List archives are viewable at: //www.freelists.org/archives/si-list or at our remote archives: http://groups.yahoo.com/group/si-list/messages Old (prior to June 6, 2001) list archives are viewable at: http://www.qsl.net/wb6tpu