The method you described, measures the potential difference between the GND of CRO and your GND. (If you consider the GND of CRO as a Good reference) If you have a differential probe you can try these with its gnd connected to one of the measuring points (you may use 2 single ended probes with their gnds clipped together, but have more loop length/inductance which gather more noise) You may measure Ground Bounce as 1) Difference between the potential of GNDs at point you are interested and at the power source (o/p of Regulator or Power entry point of card which ever is applicable) 2) Difference between the potential of GNDs at points. Eg: GNDs at Source Buufer and GND at load buffer The second one seems more relevant to me. Refer High-Speed Digital Design, by Howard Johnson for better understanding Joe Paul -----Original Message----- From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] On Behalf Of ospyng Sent: Wednesday, April 06, 2005 11:53 AM To: si-list@xxxxxxxxxxxxx Subject: [SI-LIST] How to Measure Ground Noise hi, I was taught to measure ground noise, by having the ground of the probe connect to ground TP of the board and the tip of the probe measuring the same TP. is this the correct where? and Why? is it because of the ground cable (3 inch) cause a loop, therefore the reference and the tip of the probe has a different voltage? thanks pyng ------------------------------------------------------------------ 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