Dave, Will a varistor (shunt), inductor (series) help for this case? I don't have any simulator to try. Thanks. Regards, Celine > Date: Thu, 15 Nov 2007 20:03:42 -0700> From: telegrapher9@xxxxxxxxx> To: jeetshah@xxxxxxxxx> Subject: [SI-LIST] Re: On-Chip Parasitic C & its effect on R> CC: si-list@xxxxxxxxxxxxx> > Jitesh,> > does your chip have ODT? I ran a frequency domain sim using an> electronic Smith Chart and adding an inductor didn't help. I'm able to> rapidly sweep various component values and did not obtain good return> loss until adding some series resistance. Of course to keep the delay> low and not attentuate the signal too much this value I limited to 25> ohms. Here is the model:> > 12 ps, 50 ohm t-line. 50 ohm ODT shunt. 25 ohms series resistor. 400> fF shunt, 5 ohm series, 400 fF shunt.> > This was modeled single-ended. Your application is differential, is> it? Also, the 25 ohm series resistor isolates the ESD circuitry. Not> good but this might lead to some more insight into this matching> problem. The ESD circuitry and driver/receiver are modeled as the 400> fF, 5 ohm, 400 fF.> > Dave Cuthbert> Consultant> > > On Nov 15, 2007 5:48 PM, Jitesh Shah <jeetshah@xxxxxxxxx> wrote:> > Hi Everybody,> >> > I am designing a flip chip package for multi-Gbps> > SerDes (6.25Gbps & above) where as a stand alone> > package, I am able to optimize the flip-chip> > interconnect structure to meet the return loss> > specification of 10dB for up to 2x the fundamental> > switching frequency i.e., 10GHz.> >> > But due to the on-chip parasitic capacitance (~800fF)> > associated with the transmit driver circuitry and the> > ESD structures around it, the chip+package return loss> > degrades significantly and violates the 10dB spec.> >> > I was hoping to design an inductor on package to> > compensate for this cap and to bring the odd-mode Z to> > 50Ohms but in the TDR profile, the impedance> > discontinuity created by the chip C and the package> > impedance discontinuity occur at different times. So> > regardless of what structural optimization I do> > on-package, it does not improve the overall> > chip+package RL performance.> >> > Can anybody shed some light on this or point me to> > some resources I can use.> >> > Regards,> >> > Jitesh Shah> > Advanced Package Design> > IDT> >> >> >> >> > ____________________________________________________________________________________> > Be a better sports nut! Let your teams follow you> > with Yahoo Mobile. Try it now. http://mobile.yahoo.com/sports;_ylt=At9_qDKvtAbMuh1G1SQtBI7ntAcJ> > ------------------------------------------------------------------> > 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> >> >> >> ------------------------------------------------------------------> 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> > _________________________________________________________________ Feel like a local wherever you go. http://www.backofmyhand.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 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