Alan, No, the bulk caps are electrolytic. Anand. From: "Pfeifer, Alan" <apfeifer@xxxxxxxx> on 08/08/2002 11:09 PM To: ANAND KURIAKOSE/Apex Data Inc/01@Apex Data Inc, si-list@xxxxxxxxxxxxx@SMTP@Exchange cc: =20 Subject: RE: [SI-LIST] Noise on BGA core voltage rail =A0=20 Anand,=20 Are the buld capacitors ceramic?=A0 If so, it might help to remove these.=20 Alan=20 -----Original Message-----=20 From: Anand.Kuriakose@xxxxxxxxxx=20 To: si-list@xxxxxxxxxxxxx=20 Sent: 8/8/02 9:36 AM=20 Subject: [SI-LIST] Noise on BGA core voltage rail=20 Hi,=20 Heres a situation where i have a BGA (chipset with interface to=20 processor, DDR=20 memory and other high speed proprietry buses) with sufficient decoupling=20 sprinkled around the BGA. The decoupling on the core voltage rail (2.5V,=20 which=20 is also the I/O voltage for DDR interface)=A0 basically consists of 2 high=20 value=20 bulk capacitors, six 1uf caps, ten each of 0.1uF and 0.01uF caps. I am=20 noticing=20 noise around 150mv of noise during activity on the DDR (using software=20 utilities) and roughly 80-100 mV=A0 during almost no activity across the=20 chip.=20 This amplitude is significantly more than the noise noticed at other high speed=20 chips on the board. Using the FFT function on the DSO, i figured out that the=20 frequencies where it peaks are 200Mhz and integral multiples of 200Mhz.=20 I tried a couple of things:=20 1>=A0=A0 Since i am seeing peaks at 200Mhz and its integral multiples, = i thought=20 that there could be insufficient high frequency decoupling and hence i=20 replace=20 the=A0 0.1uF caps with 1000pF caps.=20 2>=A0=A0 Secondly, fearing that there could be some resonance = happening due=20 the=20 different values of caps used, i replaced all the 0.1 uF caps with=20 0.01uF caps=20 (in=A0 addition to existing 0.01uF caps).=20 Both the above strategies failed to reduce the noise. There was no=20 change in the=20 amplitude of the noise and also the frequencies where peaks were=20 noticed.=20 Can somebody out there throw some light on what is lacking in the=20 strategies=20 mentioned above and how to reduce this noise satisfactorily.=20 Thanx in advance.=20 Anand.=20 ------------------------------------------------------------------=20 To unsubscribe from si-list:=20 si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field=20 or to administer your membership from a web page, go to:=20 //www.freelists.org/webpage/si-list <//www.freelists.org/webpage/si-list>=20 For help:=20 si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field=20 List archives are viewable at:=A0=A0=A0=A0=20 =A0=A0=A0=A0=A0=A0=A0 =A0=A0=A0=A0=A0=A0=A0 = //www.freelists.org/archives/si-list <//www.freelists.org/archives/si-list>=20 or at our remote archives:=20 =A0=A0=A0=A0=A0=A0=A0 =A0=A0=A0=A0=A0=A0=A0 = http://groups.yahoo.com/group/si-list/messages <http://groups.yahoo.com/group/si-list/messages>=20 Old (prior to June 6, 2001) list archives are viewable at:=20 =A0=A0=A0=A0=A0=A0=A0 =A0=A0=A0=A0=A0=A0=A0 http://www.qsl.net/wb6tpu <http://www.qsl.net/wb6tpu>=20 =A0=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 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