Herman, thanks for the additional explanation. my answer might have been too brief. What I meant is, that every S-parameter set (especially in touchstone format) comes with a common reference, and this can result in strange or wrong results depending on what you put together, and how. E.g. if you have a channel consisting of two "isolated" Transceivers connected with only a twisted pair for data. In simulation, you could use 2 S-Parameter sets (one transceiver, one cable) If you connect all reference points of the s-parameters to GND, you open a very short return path for common modes which is definitely not there in reality. Or imagine a huge daugtercard. the "GND" will not have a clean 0 voltage all across the plane, but S-parameters of this daughtercard will have this fixed 0 Voltage, as they only have one reference node. When you directly measure S-Parameters with a VNA, the coax cables bring the GND for each Port directly to the DUT. If your DUT has different reference voltages at each port, you can not measure directly. This is what I meant with "all referenced to GND" BR Gert ---------------------------------------- Absender ist HARTING Electronics GmbH, Marienwerderstraße 3, D-32339 Espelkamp; Registergericht: Amtsgericht Bad Oeynhausen; Register-Nr.: HRB 8808; Vertretungsberechtige Geschäftsführer: Dipl.-Kfm. Edgar-Peter Düning, Dipl.-Ing. Torsten Ratzmann, Dr.-Ing. Alexander Rost -----Ursprüngliche Nachricht----- Von: herman_westra@xxxxxxxxxxx [mailto:herman_westra@xxxxxxxxxxx] Gesendet: Mittwoch, 19. Dezember 2012 16:54 An: Havermann, Gert; shine2828@xxxxxxxxx; si-list@xxxxxxxxxxxxx Betreff: RE: [SI-LIST] AW: Help Gert, [...] that S-Parameters are based on the idea of "GND", and they all reference to GND. [...] Not quite so. S-parameters describe the relationship (magnitude and phase) of 'power waves' (voltage, current of a sinusoidal signal referenced to a specified Z0) incident onto and scattered from a multi-port electrical network (Sji). Each port has two terminals (+ and - to allow the phase relationships to be described unambiguously). S-parameters contain no information about the relationship (and do not require a connection) between any of the two terminals of a port to any terminal of any other port. Ports of an S-parameter network are floating (with respect to each other and wrt to "GND"). All current going into a port's + terminal comes out of the - terminal of the same port (or vice versa). The ONLY thing that S-parameters describe is (again) the magnitude/phase relationship between a wave entering the network at port i and the wave scattered (reflected/transmitted) from port j (Sji). In many circuit simulators the minus terminals of the ports of S-parameter-based models are tied together to a common pin. This is not related to how the S-parameters were measured/EM-simulated and does not change the behavior of the model. The common pin can be connected to the circuit simulator's node 0 or GND, but this is not a requirement and only dependent on the intended overall circuit to be simulated. Regards, Herman Westra Application Engineer Agilent EEsof EDA -----Original Message----- From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] On Behalf Of Havermann, Gert Sent: Tuesday, 18 December, 2012 14:05 To: shine2828@xxxxxxxxx; si-list@xxxxxxxxxxxxx Subject: [SI-LIST] AW: Help Joy, S-Parameter have advantages and disadvantages you should know about before you start using them. One advantage is, that S-Parameters can include quite complex channel geometries with coupling, components, connectors and discontinuities which are hard to model just with transmission lines. One disadvantage is, that S-Parameters are based on the idea of "GND", and they all reference to GND. There are many other aspects. S-Parameters are just as good as the way they were achieved, and transmission lines are just as good as their model. There has been a nice tutorial at DC2012: http://blogs.synopsys.com/analoginsights/files/2012/02/BradBrim_TutorialSlides_final1.pdf This is also helpful information: http://www.eetimes.com/electronics-news/4154786/Using-S-parameters-for-signal-integrity-analysis There are many other links to be found with google, bing or other search engines. BR Gert ---------------------------------------- Absender ist HARTING Electronics GmbH, Marienwerderstraße 3, D-32339 Espelkamp; Registergericht: Amtsgericht Bad Oeynhausen; Register-Nr.: HRB 8808; Vertretungsberechtige Geschäftsführer: Dipl.-Kfm. Edgar-Peter Düning, Dipl.-Ing. Torsten Ratzmann, Dr.-Ing. Alexander Rost -----Ursprüngliche Nachricht----- Von: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] Im Auftrag von Joy Christian Gesendet: Dienstag, 18. Dezember 2012 12:06 An: si-list@xxxxxxxxxxxxx Betreff: [SI-LIST] Help Hi, I am using Scattering parameter based channel in my design. Can anyone please tell me the advantages of Scattering parameter over transmission line? Thanks, Joy ------------------------------------------------------------------ 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 forum is accessible at: http://tech.groups.yahoo.com/group/si-list 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 forum is accessible at: http://tech.groups.yahoo.com/group/si-list 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 forum is accessible at: http://tech.groups.yahoo.com/group/si-list 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