A direct link to a partial of Howard Johnson has a video about Via Inductance: http://www.sigcon.com/SiLab/Via_clip.wmv ss -----Original Message----- From: Hill, John [mailto:John.Hill@xxxxxxxxxx] Sent: Tuesday, December 12, 2006 6:51 AM To: chand_374@xxxxxxxxx; Salkow, Steven; PaulClarke@xxxxxxxxxxxxx; si-list@xxxxxxxxxxxxx Subject: RE: [SI-LIST] Re: ROOKIE: Anti-Pad Size Effect On Signal Integrity:By the formula, as F goes up, Xc goes down (was up by typo) Chand, Howard Johnson has a video about Via Inductance where he tunes a via. There is nothing like going in the lab and seeing it for yourself. Howard has captured that in his video. Here is a link to his web site: http://www.sigcon.com/SiLab/filmsNow.htm Best regards, John John Hill Design Engineer TK HOLDINGS INC Electronics 27200 Haggerty Road Suite B-12 Farmington Hills, MI 48331 Office Phone: 248 699 2915 Mobile Phone 248 765 3599 --------------------------------------- The information in this email and attachments hereto may contain legally privileged, proprietary or confidential information that is intended for a particular recipient. If you are not the intended recipient(s), or the employee or agent responsible for delivery of this message to the intended recipient(s), you are hereby notified that any disclosure, copying, distribution, retention or use of the contents of this e-mail information is prohibited and may be unlawful. When addressed to Takata customers or vendors, any information contained in this e-mail is subject to the terms and conditions in the governing contract, if applicable. If you have received this communication in error, please immediately notify us by return e-mail, permanently delete any electronic copies of this communication and destroy any paper copies. --------------------------------------- -----Original Message----- From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] On Behalf Of chand basha Sent: Tuesday, December 12, 2006 3:03 AM To: steven.salkow@xxxxxxxx; PaulClarke@xxxxxxxxxxxxx; si-list@xxxxxxxxxxxxx Subject: [SI-LIST] Re: ROOKIE: Anti-Pad Size Effect On Signal Integrity:By the formula, as F goes up, Xc goes down (was up by typo) Steven Salkow, its an excellent presentation, very simple really very simple, I have a dought in the last para i.e How do we tune via impedance? We use ground vias nearby and 3D Modeling tools that exist to fufill this purpose but that is beyond the scope of a short answer. if you can explain a littile bit about tuning the impedance with ground vias will be very much help full. Thanks in advance. chand "Salkow, Steven" <steven.salkow@xxxxxxxx> wrote: -----Original Message----- From: Salkow, Steven Sent: Monday, December 11, 2006 1:59 PM To: 'PaulClarke@xxxxxxxxxxxxx'; 'si-list@xxxxxxxxxxxxx' Subject: RE: [SI-LIST] ROOKIE: Anti-Pad Size Effect On Signal Integrity Paul: I will make this simple are seems reasonable. It does, however, seem to me quite extraordinary that a mechanical fellow might be getting involved with Gigahertz design of vias. You're correct the effect does depend on speed. The "anti-pad" is used when building plane layers (i.e.: solid layers) using negative planes. It is the VOID area between the pad and the copper of the plane. The effect is to provide a capacitive reactive effect given by the formula Xc= 1/(2*pi*F*C) where f is frequency and C is capacitance. By the formula, as F goes up, Xc goes down (was up by typo). The C capacitance is given by the formula C = (Area*k*e)/length where length is really the distance the two areas are apart (in this case the width of the anti-pad (the bigger the gap, the smaller the capacitance). The effects of C is cumulative for multiple planes. If the anti-pad size is very large, are we out of the woods. NO! All signals used in modern design as transmission lines have a certain desirable impedance. The is the effective "resistance" of the line that best matches the driver electronics. When effective "resistance" of the line does not match the driver electronics one of two possibilities happen: The signal has energy reflected back to the source Or excessive energy is absorbed by the circuit a too little gets to the load. Anti-pads are designed to maintain the required effective "resistance" (impedance) of a transmission line at a matching value. What's that mean? If the line impedance and the driver impedance and the load impedance are all 50 ohms, then the via should be tuned to the same value. How do we tune via impedance? We use ground vias nearby and 3D Modeling tools that exist to fufill this purpose but that is beyond the scope of a short answer. Steven Salkow Lockheed IS&S 3130 Zanker Rd, San Jose Ca. 94588 steven.salkow@xxxxxxxx salkow@xxxxxxxxxxxx -----Original Message----- From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] On Behalf Of Clarke, Paul Sent: Monday, December 11, 2006 1:25 PM To: 'si-list@xxxxxxxxxxxxx' Subject: [SI-LIST] ROOKIE: Anti-Pad Size Effect On Signal Integrity Hello, Before you read the question please keep in mind that I am just a lowly Mechanical guy that has better odds of selecting the right bolt than I do designing an LED circuit. I have a question about how the size of an anti-pad can effect signal integrity. The example application could be a backplane @ 5, 10, 20, 40, or 80 [G] (I am asking for this range because I anticipate the answer may depend on the speed). If you have a BP via for a signal pair of .025" with a pad of .044", how much impact can an antipad have on the impendance through a range of sizes of let's say .054-.060"? Center-Center distance could be 2.1 [mm]. In the case described above, would the antipad size range really have any effects or is it negligible? Is an anti-pad just to keep solder off the pad if you flood the plane? Or is there an actual SI reason for those things? How sensitive is the SI to changes in antipad size? Any concerns regarding manufacturing tolerances on antipads? Thank you for any information and your patience explaining any of the above questions to a mechanical guy. Paul Clarke ------------------------------------------------------------------ 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 __________________________________________________ Do You Yahoo!? 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Mail has the best spam protection around http://mail.yahoo.com ------------------------------------------------------------------ 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