Hi, Siming, Steve answered well. Using common power net in package design increase risk of: 1) conducted noise due to common impedance coupling - especially for blocks contain tens to a couple hundred kHz freq 2) increased coupling due to higher mutual inductance 3) reduced controllability if all power net are tied together Using dedicated power island with careful decoupling and PDN control is a much better design methodology. Catherine Xu __________________________________ Lead HW Design Engineer, Ph.D HP ICS CHIL - San Diego __________________________________ -----Original Message----- From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] On Behalf Of steve weir Sent: Monday, November 01, 2010 4:24 PM To: Siming Pan Cc: si-list@xxxxxxxxxxxxx Subject: [SI-LIST] Re: design of on-chip PDN Common impedance. Steve. Siming Pan wrote: > Hi All, > I have a basic question related to on-chip PDN design. Usually the supply > voltages are designed to be isolated for core, SERDES > > digital, analog, termination, etc. This design may isolate the SSN > couplings among each net. However, usually large on-chip decoupling > > capacitances are used for VDD core circuit. In the board design, we connect > the power nets of VDD_core together with VDD_digital¡£ > > Thus, switching noises generated from SERDES digital are suppressed by large > on-chip decaps designed for core circuit. However, > > package inductances still play a bad role here to block the conducted path > between noise source formed by digital circuit and core > > capacitances. Then why not use one common power net as the supply power for > all the IC circuits, so that large on-chip decaps can be > > shared, if the voltage levels are the same? > > Regards, > > Siming Pan > > > -- Steve Weir IPBLOX, LLC 150 N. Center St. #211 Reno, NV 89501 www.ipblox.com (775) 299-4236 Business (866) 675-4630 Toll-free (707) 780-1951 Fax ------------------------------------------------------------------ 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 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 Old (prior to June 6, 2001) list archives are viewable at: http://www.qsl.net/wb6tpu