Hi Sean Lu, The resistor cause phase shift from zero frequency while the ferrite bead is high frequency element. While trying to boot, the power supply inject antiphase voltage spikes into the oscillator and it stops. The use of the resistor cause the phase shift (at any frequency!!), thus moving the startup and the stop noise from each-other. Hope it helps. BTW, checking oscillator current should demonstrate very low power which means no drastic IR on it. Regards, yehuda -----Original Message----- From: lu Haizhao [mailto:luhaizhao@xxxxxxxxxx] Sent: Monday, March 31, 2003 9:31 AM To: si-list@xxxxxxxxxxxxx Subject: [SI-LIST] a problem about PLL bypass Hi,all In the Motolola's telecom controller XPC8260-200MHz's handbook,the PLL bypass circuit is the following: VDD _____ -------------|____|-----------------------VCCSYN R | | ___ ___ ___ 10uF ___ 0.1uF | | |____________| | | GND the R is 10 Ohm. In the board,I use a ferrite bead instead of a resistance.This ferrite bead has a resistance of 0.01 Ohm in steady current,and 60 Ohm in 100MHz. the problem is when the board is under -5=A1=E6 to = -30=A1=E6=A3=ACsometime the 8260 can not boot up normally or can not boot up.and if you use a resistance,not a ferrite bead,the problem will disappear. Can someone tell me the cause? Thanks! Regards, Sean Lu Huawei Technologies co.,Ltd=20 Shenzhen China=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 ------------------------------------------------------------------ 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