Excessive ground lead inductance for the probe will easily show up by probing a short (not one established with VIAS) and examining any significant resonance. I would also compliment this making a simple measurement of probe open, and if possible a short relatively low-loss THRU path. Essentially you can analyze your transmission, reflection, and directivity error terms exactly like a SOLT calibration performed on a VNA using cal kit standards. Check out http://cpd.ogi.edu/IEEE-MTT-ED/Advances%20in%20Microwave%20Error%20Correctio n%20Techniques.pdf Alfred P. Neves <*)))))><{ Hillsboro Office: 735 SE 16th Ave. Hillsboro, OR, 97123 (503) 718 7172 Business (503) 679 2429 Mobile Main Corporate office: Teraspeed Consulting Group LLC 121 North River Drive Narragansett, RI 02882 (401) 284-1827 Business (401) 284-1840 Fax http://www.teraspeed.com Teraspeed is the registered service mark of Teraspeed Consulting Group LLC -----Original Message----- From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] On Behalf Of Michael Rose Sent: Tuesday, June 08, 2010 9:15 AM To: tom; Santangelo, Steven; si-list@xxxxxxxxxxxxx Subject: [SI-LIST] Re: Correlation to lab measurement I was thinking the same thing - probably too much ground lead inductance in the probing. If you have a decent FET or resistive probe, use the spring clip on a nearby (very close) ground. If you don't have good high-speed probes you can construct a very good resistive probe using RG-174 (see Doug Smith or Howard Johnson articles) and solder directly to the measurement point. Also, many high-speed probes include a small series resistor accessory at the tip to dampen the ringing. Mike -----Original Message----- From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] On Behalf Of tom Sent: Tuesday, June 08, 2010 11:54 AM To: 'Santangelo, Steven'; si-list@xxxxxxxxxxxxx Subject: [SI-LIST] Re: Correlation to lab measurement It could very well be the simulations are correct and your measurements are tainted by poor measurement technique. Probing boards that were never designed to be probed can be very problematic. Probing is a SI problem and the key to good SI is keeping an eye on the return currents. The ground lead in your probing system looks like an inductor which can cause a resonant circuit with the input capacitance of the scope probe. Whenever a resonant circuit is stimulated with an edge ringing will occur. If your probe point and local ground return point are not very close to each other, say less than 0.100" and your "ground lead" is almost nonexistent in length then you will have ringing in your scope's display. When you probe a board you need to think in terms of how closely your scope probing system approximates a coaxial connection to the board. How well are the fields contained in the probing system? Hope this helps. Tom Dagostino Teraspeed Labs 13610 SW Harness Lane Beaverton, OR 97008 503-430-1065 tom@xxxxxxxxxxxxx www.teraspeed.com Teraspeed Consulting Group LLC 121 North River Drive Narragansett, RI 02882 401-284-1827 www.teraspeed.com -----Original Message----- From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] On Behalf Of Santangelo, Steven Sent: Tuesday, June 08, 2010 7:23 AM To: si-list@xxxxxxxxxxxxx Subject: [SI-LIST] Correlation to lab measurement Hi All, I'm trying to correlate some lab measurements to my simulations in Cadence PCB SI (SpectraQuest). I have a 400MHz unidirectional LVDS interface between two Xilinx devices that is terminated in 100ohms inside one of the devices. My lab measurements show a pretty good reflection occurring on the rising and falling edges of the waveform. I'm trying to determine if this is being caused by the ball to I/O pad trace length in the package (plus my BGA breakout). My simulation only shows a slight bend in the waveform rather than the non monotonic ring that I see in the lab. The bend does correlate well time wise (location on the edge) with the lab measurement. I don't really know much about the limitations of IBIS models so I'm wondering if some of the discrepancy could be due to that. FYI: I'm using the models that Xilinx "ibiswriter" puts out. The rise/fall times of the waveforms are in the neighborhood of 300pS. Thanks Steve ------------------------------------------------------------------ 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 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 technical documents are available at: http://www.si-list.net List archives are viewable at: //www.freelists.org/archives/si-list 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 technical documents are available at: http://www.si-list.net List archives are viewable at: //www.freelists.org/archives/si-list 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 technical documents are available at: http://www.si-list.net List archives are viewable at: //www.freelists.org/archives/si-list Old (prior to June 6, 2001) list archives are viewable at: http://www.qsl.net/wb6tpu