Dear Bala I suggest that the 1M ohm should not be used because of resonance. In our measurement, there is the following setting <20MHz 1M ohm could be used for the frequency is too low for resonance. full bandwidth 50 ohm should be applied to avoid resonance. Hope this is helpful. Best Regards Zhangkun 2006.3.20 ----- Original Message ----- From: "BalaKrishnan, Kesavaperumal (IE10)" <BalaKrishnan.Kesavaperumal@xxxxxxxxxxxxx> To: <si-list@xxxxxxxxxxxxx> Sent: Monday, March 20, 2006 8:53 PM Subject: [SI-LIST] Measuring Power supply noise > Hi, > > > To measure the noise of the power plane (We use LDO to generate 5V), > > > > I did the following > > a) I built a cable using a 50?Coax cable and used the internal termination of > the oscilloscope. > > b) Removed a CAP from the board, used these PADS to solder my probe. > > > > The noise measured was around 20mV > > > > To check the sanity of my measurement, Instead of my 50?probe, I used a > standard 1M?probe and carried out the measurement. > > The measured noise was around 50mV > > > > I have the following question. > > > > a) By using a 50?probe, did I create a voltage divider? > > > > Thanks in advance for your time. > > > > Regards, > > Bala > > > > > ------------------------------------------------------------------ > 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 FAQ wiki page is located at: > http://si-list.org/wiki/wiki.pl?Si-List_FAQ > > List technical documents are available at: > http://www.si-list.org > > 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 > > ------------------------------------------------------------------ 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 FAQ wiki page is located at: http://si-list.org/wiki/wiki.pl?Si-List_FAQ List technical documents are available at: http://www.si-list.org 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