A solid Tantalum capacitor has ESR of several hundred milliohms, whereas ESR of a Ceramic capacitor is about 10 -20 milliohms. Perhaps this is what makes such a large difference in the noise reduction properties for the two types of capacitors. Another experiment you can try is to replace the Tantalum capacitor with a Polymer Tantalum capacitor, which has ESR below 100 milliohms. If this causes significant reduction in power supply noise then ESR is the key factor. Regards, Ravinder Server PCB and Flex Development Hitachi Global Storage Technologies Email: Ravinder.Ajmani@xxxxxxxx Zhangkun <zhang_kun@xxxxxxxxxx> Sent by: si-list-bounce@xxxxxxxxxxxxx 12/04/2003 03:50 AM Please respond to zhang_kun To: si-list <si-list@xxxxxxxxxxxxx> cc: From: si-list-bounce@xxxxxxxxxxxxx Subject: [SI-LIST] nonlinear in power ground noise of clock driver Dear All: Recently, my colleague found out something interesting about clock driver. In our product, CDC2516 of TI is used as clock driver. The clock frequency is 100MHz. The power of CDC2516 is isolated by one bead. There is some local decoupling caps as following: several 0.1uF or 0.01uF ceramic cap one 10uF tan cap We measure the power ground noise of CDC2516. The power ground noise is about 700mV. The spectrum of the noise is at 100MHz, 200MHz, 300MHz, and so on. We use several method to decrease the noise. Theere is no use. My colleague change the 10uF tancap to one 10uF ceracap(X7R). The noise decrease to 17mV. I am a little confused. I have simulate the impedance of decoupling circuit. There is no difference in frequency domain beyond 30MHz between using 10uF tancap and 10uF ceracap. According to my experience, the power ground noise should not decrease. I think there is something nonlinear. I am not familar with the circuit of clock driver. There is no SPICE model of CDC2516 in TI website. Therefore I could not simulate the power ground noise. Could you give me some advice? Best Regards Zhangkun 2003.12.4 ------------------------------------------------------------------ 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.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 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