Hi Lakshmi, When you say 'less common mode noise', I assume you refer to time-domain common mode voltage with a given data rate and data pattern excitation, correct? In a typical channel with a connector and multiple traces, chances are that the mode conversion is frequency dependent. The peaks and minima of the mode conversion very well may depend on delays among discontinuities as well, so when you change the length, or the reflection, or the attenuation, it may shift the modal conversion curves left or right and up/down. If you have not done so yet, it would be very useful to compare the end-to-end S parameters for the two cases in the frequency domain to see if they make sense to you. Regards, Istvan Novak Oracle On 6/9/2011 7:28 AM, Lakshmi Narayanan Sowrirajan, ERS-HCLTech wrote: > Hi Steve, > > Thanks for the reply, please find the details as below. > > 1) DRV---brkout---via---8inch routing-----via----conn---4inch > routing----termination (x_p,x_n) > > 2) DRV---brkout--- 8inch routing-----conn---4inch routing----termination > (x_p,x_n) > > Signal is probed near termination and we see less common mode noise in case > 1, where we have via (modeled in HFSS as s4p) > > Common mode noise = (v(x_p)+V(x_n))/2 > > Thanks& Regards > Lakshminarayanan. S > 9840250902 > > > -----Original Message----- > From: steve weir [mailto:weirsi@xxxxxxxxxx] > Sent: Thursday, June 09, 2011 4:32 PM > To: Lakshmi Narayanan Sowrirajan, ERS-HCLTech > Cc: si-list@xxxxxxxxxxxxx > Subject: Re: [SI-LIST] Differential line Via - affecting common mode noise > > Where and how are you measuring your CM noise? Virtually all vias > impose insertion loss. Non-transparent vias insert reactive > discontinuities. > > Steve > On 6/8/2011 11:49 PM, Lakshmi Narayanan Sowrirajan, ERS-HCLTech wrote: >> Hi Experts, >> How the via improve or degrade the differential lines >> common mode noise and performance as I am getting more common mode noise for >> a case where I don't have any via. If I include a transition via (modeled in >> HFSS - s4p model) the common mode noise is getting reduced. Please direct me >> to a good article/paper/book to understand the theory behind this. >> >> Thanks& Regards >> Lakshminarayanan. S >> >> >> ________________________________ >> ::DISCLAIMER:: >> ----------------------------------------------------------------------------------------------------------------------- >> >> The contents of this e-mail and any attachment(s) are confidential and >> intended for the named recipient(s) only. >> It shall not attach any liability on the originator or HCL or its >> affiliates. Any views or opinions presented in >> this email are solely those of the author and may not necessarily reflect >> the opinions of HCL or its affiliates. >> Any form of reproduction, dissemination, copying, disclosure, modification, >> distribution and / or publication of >> this message without the prior written consent of the author of this e-mail >> is strictly prohibited. If you have >> received this email in error please delete it and notify the sender >> immediately. Before opening any mail and >> attachments please check them for viruses and defect. >> >> ----------------------------------------------------------------------------------------------------------------------- ------------------------------------------------------------------ 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