Ray I use bead and caps. The caps is of 10uF(Tan), 0.1uF(cera), and 0.01uF(cera). Best Regards Zhangkun 2004.8.28 ----- Original Message ----- From: "Ray Anderson" <reanderson@xxxxxxxxxxxxx> To: <zhang_kun@xxxxxxxxxx> Cc: "steve weir" <weirsp@xxxxxxxxxx>; <si-list@xxxxxxxxxxxxx> Sent: Friday, August 27, 2004 10:26 PM Subject: [SI-LIST] Re: [Bulk] Re: Decoupling for PLL > Zhangkun- > > Can you tell us what values of L and C you are using in your filter ? > > One other thought that I had, which may or may not bear on this > particular problem is this: > > Besides isolating the noise on the PDS from your PLL, the low pass > filter also, to some extent, prevents noise generated by the PLL from > getting back onto the main PDS planes or busses. A simple L section > filter (N=2) operating in the backwards direction (CL versus LC) will > exhibit a different impedance on the "L" side than it does on the "C" > side. I'm wondering if it is possible that you might be developing some > noise at the PLL pin across the impedance of the filter L that you don't > develop across the zero ohm resistor? Perhaps your PLL likes seeing a > very low Z at it's power pin..... > > Just a thought, perhaps not relevant, but I thought I'd through it out > for discussion. > > -Ray > > > Zhangkun wrote: > > >steve > > > >I have measured the power ground noise by spectrum analyzer. There is no > >obvious difference. > > > >At some frequency, when the inductor(bead) is changed to resistor, the power > >ground noise become larger. I am confusing. > > > >Best Regards > > > >Zhangkun > >2004.8.27 > > > > > . > ------------------------------------------------------------------ > 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?Si-List_FAQ > > 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?Si-List_FAQ 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