Ravinder, Depending on the configuration of the driver, and at the expense of the leading edge rate, you can use a low value X2Y cap on the driving end with one each of the A and B terminals attached to the differential signals, and the G1/G2 terminals both attached to logic ground. This is the so-called "circuit 1" configuration. The magnetic coupling between the A and B circuits will greatly equalize the net current launched into the transmission lines beyond the capacitor. Regards, Steve. At 01:48 PM 3/29/2004 -0800, Lee Ritchey wrote: >Ravinder, > >There are a couple of ASIC suppliers who have package design problems that >lead to common mode problems in the form of Vcc and ground bounce. If you >have one of those, there is nothing you can do at the board level to fix >the problem. > >Lee > > > > [Original Message] > > From: <Ravinder.Ajmani@xxxxxxxx> > > To: <si-list@xxxxxxxxxxxxx> > > Date: 3/29/2004 9:13:16 AM > > Subject: [SI-LIST] Common-mode noise on LVD Drivers > > > > Hi All, > > There was a thread some time back about differential to common-mode > > conversion. My problem is also in this area. I have two similar ASICs > > with multiple LVD drivers. On one ASIC, I measure common-mode noise >about > > 20 dB higher than the other. Even within this ASIC, some bits show about > > 6 dB more common-mode compared to the quietest bits. The two ASICs are > > from different vendors, and the one with higher CM noise uses faster 11 >uM > > technology. I don't know the technology of the other ASIC, but its die > > size is considerably larger. This high common-mode noise is causing EMI > > problem, which I am trying to fix. I have tried changes in the card > > decoupling scheme but it does not make any difference. I am convinced > > that the common-mode noise is coming out of the ASIC, and the PCB > > improvements may not help. Is there any way to come to a definite > > conclusion about this, and is there anything I can do besides placing > > common-mode ferrite beads on every driver pair. > > The ASIC uses a core voltage of 1.8V, and has on-board regulators to > > regulate 3.3V input to 1.8V. > > I will really appreciate your help in solving this puzzle. > > Regards, Ravinder > > Server PCB Development > > Hitachi Global Storage Technologies > > > > Email: Ravinder.Ajmani@xxxxxxxx > > > > ------------------------------------------------------------------ > > 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 > > > > 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 > >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 > Steve Weir Teraspeed Consulting Group LLC 2926 SE Yamhill St. Portland, OR 97214 (503) 239-5536 http://www.teraspeed.com ------------------------------------------------------------------------------------------------------ Teraspeed(SM) is the service mark of Teraspeed Consulting Group LLC ------------------------------------------------------------------ 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 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