Getting credible results using a VNA on very low impedances requires a Kelvin connection. In any instance, impedance varies locally across the board, being higher at the edges and presumably lower in the vicinity of a bypass cap (depends on size, mounting details, etc.) A TDR is a more natural instrument for probing around the board to view this. This is was a demo at the EMC Symposium last year. Orin Laney On Thu, 6 Aug 2009 14:52:54 -0400 rula.bakleh@xxxxxxxxxx writes: > Hi Everyone, > > > I'm trying to validate our power integrity tools/simulations and I > would > like to make some power integrity measurements of our planes. > > > > With respect to performing these measurements, I plan to use a > Vector > Network Analyzer (VNA) to measure the plane impedances of a bare PWB > and > a PWB with a voltage plane that is populated with only caps in order > to > correlate these measurements to the simulations. I also plan to > measure > the plane impedance of a fully populated PWB, just to see the > effects > that other parts' impedance/mounting would have on the plane > impedance. > > > > I also plan to use a spectrum analyzer to measure the plane noise > spectrum of a powered up module and use an oscilloscope to measure > absolute levels of this noise. The purpose of using a spectrum > analyzer/oscilloscope is to measure the simultaneous switching > effects > on the plane, hoping to isolate the PWB effects from internal SSO > effects of a component. > > > > My dilemma is the following: > > The VNAs are optimized for 50 ohms and plane impedances of PWBs are > designed for very low impedance (most of the time much <1.0 ohm). > > 1) Due to the impedance discontinuities, what is the expected > accuracy > of such a measurement? > > > > All the research I have conducted concerning PWB impedance > measurements > points to using a VNA. During my discussions with an Agilent FAE, > he > recommended using an Impedance Analyzer vs. VNA to measure the PDS > of a > plane. He also recommended using a high impedance active solderable > probe with the impedance analyzer with it being calibrated out to > make > this measurement. > > > > 2) What is the best equipment to use to measure the PDS of a PWB > (VNA or > Impedance Analyzer)? > > 3) If the answer is an Impedance Analyzer, is the approach described > above correct? > > 4) Can somebody validated my approach for this type of > analysis/measurements? > > > > > Thank You, > > Rula > > > > > > > > > ---------------------------------------------------- > 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 technical documents are available at: > http://www.si-list.net > > 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 > > > ____________________________________________________________ TEFL Certificate Courses. Internationally accredited courses. Locations worldwide & TEFL Online. http://thirdpartyoffers.juno.com/TGL2141/c?cp=wdwatq1vR0VOgkXOAPvtigAAJ1CsWc805Xl0Wg7v9ZPBTMCfAAUAAAAAAAAAAEGCYj6OUaQ535RAUkPUeKN_-C4mAAAAAA== ------------------------------------------------------------------ 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 technical documents are available at: http://www.si-list.net 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