For UMC .18u standard CMOS technology, we've found that the device cap is about 8.8ff/um^2. In .25u process its about 5-6ff/um^2. 100pF would then be about 11000um^2, assuming a .18um process node. For 100+ channels this is 1million um^2. ( i.e. 1mm x 1mm die area just for decoupling i/o) Kenneth W. Egan Chief Technology Officer Vizionware, Inc. 12708 Riata Vista Circle, #A115 Austin, Texas 78727-7167 (512) 493-9660 (main) (512) 493-9663 (direct) (512) 470-7404 (cell) (512) 493-9661 (fax) kegan@xxxxxxxxxxxxxx -----Original Message----- From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] On Behalf Of Chris Cheng Sent: Wednesday, April 09, 2008 1:28 PM To: leeritchey@xxxxxxxxxxxxx; Stephane Tremblay; si-list@xxxxxxxxxxxxx Subject: [SI-LIST] Re: On-die caps for IO supply Do you have any idea how large an area 100pf will cost ? Do you have any = idea how much yield impact it will do with a 100+ DDR channel I/O ? -----Original Message----- From: Lee Ritchey [mailto:leeritchey@xxxxxxxxxxxxx] Sent: Wednesday, April 09, 2008 11:12 AM To: Chris Cheng; Stephane Tremblay; si-list@xxxxxxxxxxxxx Subject: RE: [SI-LIST] Re: On-die caps for IO supply A common number I have seen used for 3.3V drivers is 100 pF per I/O. = Seems to work on many memory die. Simulation would determine if this is good enough. > [Original Message] > From: Chris Cheng <Chris.Cheng@xxxxxxxx> > To: Stephane Tremblay <strembl1@xxxxxxxxxx>; <si-list@xxxxxxxxxxxxx> > Date: 4/9/2008 10:56:40 AM > Subject: [SI-LIST] Re: On-die caps for IO supply =20 > > I don't think you will like my answer but my experience is fill it up = =3D > with as much capacitor your technology people allow. > If you are core limited, you are SOL to begin with. > If you are pad limited, just fill the gap between the core and pad = area =3D > with decoupling cap before the yield police or the core power =3D > distribution guy wants to take it for himself. > It will take a lot more than "XXX from Si-list recommended this" to = grow =3D > your die to fit anything more than the above. > > -----Original Message----- > From: si-list-bounce@xxxxxxxxxxxxx > [mailto:si-list-bounce@xxxxxxxxxxxxx]On Behalf Of Stephane Tremblay > Sent: Wednesday, April 09, 2008 7:33 AM > To: si-list@xxxxxxxxxxxxx > Cc: 'Stephane Tremblay' > Subject: [SI-LIST] On-die caps for IO supply > > > Hi SI-Listers, > I am looking for a rule of thumb on the required on-die =3D > capacitors needed for proper operation of a given IO (a DDR mem IO in = my =3D > case). I am looking for a number of "x" capacitance per IO. > > My IO can be programmed to 18 Ohms of drive and the measured slew-rate = =3D > is slightly higher than 6 V/ns for both rise and fall. The parasitic = =3D > capacitance of this IO is about 3.5 pF. The toggle rate could be as = high =3D > as 2 Gbps so I expect the IO rail to recover within reasonable limits = =3D > within half a period. > > I could always start by assuming the current I need just for the =3D > transmission line (being a 50 Ohms one): > > dI/dt =3D3D 6 V/ns / 50 Ohms =3D3D 120 mA / ns (per IO) > > but this basic current demand calculation neglected the parasitic =3D > capacitance of 3.5 pF. > > Some will say it is also greatly dependant of my power-gnd loop =3D > inductance from IO to on-package decaps. On the other end, if my noise = =3D > spectrum is in the hundreds of MHz, I can't do much at the package = level =3D > to clean my die supply. > > So from your experience and knowledge, what would be a good start as = a =3D > required on-die capacitance required. I want to avoid my on-die IO = rail =3D > collapsing at a frequency that my package could not keep up. > > Thanks for the answers, > Steph. > =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 technical documents are available at: > http://www.si-list.net > > 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 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 ------------------------------------------------------------------ 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