Hi, Smith, For resonance, it depends on what is your interest? For SI, Simon's explanation is good enough. For PI, we can also see the resonance on power plane. In spite of any kind of resonance, the root cause is the L and C in the circuit. Just as Simon said, the via stub contains L and C by its physical structure. So, for the power delivering capability, there is the same thing from regulator to your power consumer. At which frequency the resonance will be? This question is go general. The resonance frequency is decided by the equivalent inductance and capacitance. Shao Peng 邵 鹏 Consultant Mentor Graphics Electronic Technology Co., Ltd. -----邮件原件----- 发件人: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] 代表 Lambert Simonovich 发送时间: 2011年3月25日 11:30 收件人: 'John Smith'; si-list@xxxxxxxxxxxxx 主题: [SI-LIST] Re: Resonance on the pcb board Hi John, I assume you are looking at the insertion loss plot results (SDD21) from a VNA measurement of the channel. Do you also see resonance at around 10-12 GHz? Briefly, resonances occur because of long via stubs or timing skew between the two traces of the differential pair. Timing skew is a result of differential trace lengths mismatch and/or fiber weave effect, where one trace happens to land over the glass fiber weave within the dielectric, and the other trace is over mostly resin for a portion of the total length. If your board is thick, and the trace is routed near the top layer leaving the remainder of the via as a stub, then that could be the issue, or you could have a skew issue. You might also want to review the layout and see if there is an unterminated branch trace(s) attached to the traces you are measuring that also act as a stub(s). In any event, I have recently written some blog posts on PCB vias and fiber weave effect modeling and other useful topics you might find helpful. In them I touch on resonances. They can be found at: http://blog.lamsimenterprises.com/ You can also visit my web site and download white papers on both topics at: http://lamsimenterprises.com/ Regards. Bert Simonovich Backplane Specialist and Founder LAMSIM Enterprises Inc. Web Site: http://lamsimenterprises.com Blog: http://blog.lamsimenterprises.com/ -----Original Message----- From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] On Behalf Of John Smith Sent: March-24-11 10:21 PM To: si-list@xxxxxxxxxxxxx Subject: [SI-LIST] Resonance on the pcb board Hi, Experts, I am new to signal integrity and I have some questions. (1) I did some measurements on my pcb board and found resonances around 3.5GHz. Can you give me some hints on what causes the resonances? (2) Could you please list some typical issues which can cause resonances and at what frequency range? I know dielectric loss can cause resonance at around 25GHz, what about the other effects? Thanks in advance. Regards, John ------------------------------------------------------------------ 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.net List archives are viewable at: //www.freelists.org/archives/si-list 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.net List archives are viewable at: //www.freelists.org/archives/si-list 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.net List archives are viewable at: //www.freelists.org/archives/si-list Old (prior to June 6, 2001) list archives are viewable at: http://www.qsl.net/wb6tpu