Hi Steve, Yes I see that but typically don't you want a low ESR cap for low power distribution imedance after \the ferrite. This isn't an issue with plane resonance (I think!) 20nH and 4.5uF have a resonance at 500kHz or so. So its possible that the bulk cap is reonating with the ferrite and its connections? -----Original Message----- From: steve weir [mailto:weirsp@xxxxxxxxxx] Sent: Sunday, September 05, 2004 6:55 PM To: zhang_kun@xxxxxxxxxx; cgrassosprint1@xxxxxxxxxxxxx Cc: si-list Subject: Re: [SI-LIST] Re: Decoupling for PLL (continued) Charles and Zhangkun, if this is a series LPF somewhere in that network you need enough resistance to damp out the reactive impedance. If you just have a ferrite bead and a low ESR ceramic then Zhangkun is right, that network will have a high Q. If this is a filter constructed as a shunt notch ( unusual ), then depending on the external network, it may or may not peak. Steve. At 08:59 AM 9/6/2004 +0800, Zhangkun wrote: >Chas > >Ceramic cap is of no use. It is easy to resonate when low ESR caps are used. > >Best Regards > >Zhangkun >2004.9.6 >----- Original Message ----- >From: "Charles Grasso" <cgrassosprint1@xxxxxxxxxxxxx> >To: <zhang_kun@xxxxxxxxxx> >Cc: "si-list" <si-list@xxxxxxxxxxxxx> >Sent: Monday, September 06, 2004 9:36 AM >Subject: [SI-LIST] Re: Decoupling for PLL (continued) > > > > Dear Zhangun, > > > > It just so happens that I have just been fighting a > > noise problem witha ferrite bead /capacitor combo. > > In my case it turned out that a low ESR ceramic cap > > was required rather than a large electrolytic. > > > > Could this be the problem.. > > > > -----Original Message----- > > From: si-list-bounce@xxxxxxxxxxxxx > > [mailto:si-list-bounce@xxxxxxxxxxxxx]On Behalf Of zhangkun 29902 > > Sent: Saturday, September 04, 2004 4:25 PM > > To: cgrassosprint1@xxxxxxxxxxxxx > > Cc: si-list > > Subject: [SI-LIST] Re: Decoupling for PLL (continued) > > > > > > Chas > > > > I used bead. It resonated below 1MHz for the capacitor is too many. > > > > Best Regards > > > > Zhangkun > > 2004.9.5 > > > > ----- Original Message ----- > > From: Charles Grasso <cgrassosprint1@xxxxxxxxxxxxx> > > Date: Sunday, September 5, 2004 6:33 am > > Subject: [SI-LIST] Re: Decoupling for PLL (continued) > > > > > Hi Zhangkun, > > > > > > Its very important to differentiate between an inductor and a > > > ferrite bead. > > > A ferrite bead typically has minimal impedance in the kHz range > > > and really > > > only > > > starts to kick in in the 10s of MHz range. An inductor, on the > > > other hand, > > > can > > > exhibit LARGE reative impedance in the kHz range (depending on the > > > value) - > > > but > > > will also exhibit resonances that need to be damped. > > > > > > Chas > > > > > > -----Original Message----- > > > From: si-list-bounce@xxxxxxxxxxxxx > > > [mailto:si-list-bounce@xxxxxxxxxxxxx]On Behalf Of Zhangkun > > > Sent: Thursday, September 02, 2004 10:53 PM > > > To: si-list > > > Subject: [SI-LIST] Decoupling for PLL (continued) > > > > > > > > > Dear all > > > Recently, I have done some measurement. It is found that when the > > > bead(inductor) is used, the power ground noise at 333KHz from VRM > > > is larger. > > > There is some noise near the clock frequency points. > > > > > > For example, the output clock of PLL is 50MHz. At 50.333MHz and > > > 49.667MHz,there is noise, which is in proportion to the noise at > > > 333KHz. Maybe the PLL > > > modulates the noise of VRM into the output clock. > > > > > > Is there any SPICE model for PLL? > > > > > > Best Regards > > > > > > Zhangkun > > > 2004.9.3 > > > > > > > > > ------------------------------------------------------------------ > > > 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 > > > > > > > > > > > > > ------------------------------------------------------------------ > > 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 > > > > >------------------------------------------------------------------ >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