Canes - Do you have a transmission line between your driver and the load cap? I assume that you are simulating a bunch of simultaneously switching drivers that pump current into some kind of inductance matrix attached to transmission lines and load capacitors at the far end. =20 In today's technology, the driver rise and fall time is likely to be shorter than the time of flight of the transmission line. Most drivers make their transitions in less than 500pSec and the transmission line is likely to be 1000pSec (6 inches long). The driver does not feel the load cap until 2 time of flights (2000pSec) have passed, long after the SSN event is over. =20 The load cap will have no effect on the SSN waveform at the driver during the initial event but will have a huge effect in reducing the SSN seen at the far end of the transmission line because of it's filtering properties. You essentially have a 50 Ohm transmission line driving into a capacitance which implies an RC time constant. The fast edge of the SSN spike gets filtered.=20 It makes perfect sense for load capacitors at the far end of transmission lines to reduce the amount of SSN measured in that location. Regards, Larry Smith Altera Corporation -----Original Message----- From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] On Behalf Of Canes Venatici Sent: Wednesday, January 31, 2007 11:30 PM To: si-list@xxxxxxxxxxxxx Subject: [SI-LIST] SSN Vs Load cap Hi all, I couldn't understand why if load capacitance is increased, SSN is reduced (as the recommendation is increased SSO index, more signal pads can be accommodated by power pads). As di/dt is directly proportional to load cap, increasing the load causes more drop in parasitic inductance and SSN should increase. Could anyone clarify. Thanks, Canes =20 ________________________________________________________________________ ____________ Finding fabulous fares is fun. =20 Let Yahoo! FareChase search your favorite travel sites to find flight and hotel bargains. http://farechase.yahoo.com/promo-generic-14795097 ------------------------------------------------------------------ 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: =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 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