I highly doubt you need HFSS for a 5MHz design. Get you blind via dimensions and use a first order approximation of a = coxial cylinder for the capacitance and you should be GTG. -----Original Message----- From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx]On Behalf Of Leonard Dieguez Sent: Monday, July 18, 2005 1:27 PM To: david.lieby@xxxxxxxxxxx; si-list@xxxxxxxxxxxxx Subject: [SI-LIST] Re: HSPICE and Via Modeling David, I have never been very good at coming up with closed form equations for problems like that. I would create a 3D EM model in HFSS. This would model the stackup, board materials and via placement including the ground vias in the area or the return vias. Run the simulation over a representative band of frequencies and generate S-parameters. You can then import the S-parameters into Hspice or other time domain simulators with the other circuits and run your simulations. Before doing that I would optimize the via diameter, anti pad clearance, annular ring diameter, distance from ground / return via and trace thickness over anti-pad for the desired impedance matching. The optimization can be done in HFSS. By looking at the return loss and insertion loss over the frequency band will give you an idea how the via will behave. In general vias have a tendency to have a excess capacitance when compared to the trace connecting to it. Leonard Dieguez Xilinx System IO Specialist -----Original Message----- From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] On Behalf Of dav0 Sent: Monday, July 18, 2005 11:28 AM To: si-list@xxxxxxxxxxxxx Subject: [SI-LIST] HSPICE and Via Modeling I have an engineer who wants a detailed model of a via. Mostly he is looking for capacitance. The part of the system he is working on runs at less than 5 MHz. The via is blind, with the closed end of the via ending fairly close to a ground plane. __ __ Top Pad ________ ][ _____ Reference layer ][ ---------][----- routing layer 1 ---------][----- routing layer 2 ________ ][ _____ Reference layer ][ ---------][----- routing layer 3 ---------][----- routing layer 4 ________ ][ _____ Reference layer ][ ---------][----- routing layer 5 ---------][----- routing layer 6 __][__ Bottom pad, end of via _________________ Reference layer, at center of stackup the same stackup reversed. My questions: 1. Can one analyze this in HSPICE? 2. Does anyone have a spice deck with anywhere near a starting point, that they can share. The vendor support engineer could not come up with anything helpful. Thanks, dav0 David Lieby Siemens Medical, USD, MVIS-S ------------------------------------------------------------------ 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: =3D20 //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 =3D20 ------------------------------------------------------------------ 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: =20 //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 =20 ------------------------------------------------------------------ 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