Shawn, it takes db/dt to magnetically induce an EMF in the victim. Higher db/dt, means higher induced EMF. Shrinking dt surely gets you there. Steve. Shawn Zheng wrote: > Hi, > I am a little confused about the impact of return current on xtalk. Common > sense is that the higher frequency signal causes more xtalk. High frequency > return current of signal tend to concentrated on the ground under the signal > trace so as to minimize the inductance. So the current density falls off > with the distance. By contrast, at relatively low frequency the return > current tends to spread across the ground plane. So there can be a large > amount of current induced (due to return currents from many other > conductors) underneath a conductor. I wonder why we dont care about low > frequency but widely spreaded return current. On many production boards, i > think there could be quite a lot of current (from DC to very high frequency) > that flows above or underneath signal traces. The magnetic field may be weak > due to low fequency loop current. but it is getting closer to victim than > the concentrated high frequency return current. right? > of course my intuition tells me that i dont need worry about them if two > conductors stay at large distance. > > Shawn > > > ------------------------------------------------------------------ > 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 > 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 > > > > > -- Steve Weir Teraspeed Consulting Group LLC 121 North River Drive Narragansett, RI 02882 California office (408) 884-3985 Business (707) 780-1951 Fax Main office (401) 284-1827 Business (401) 284-1840 Fax Oregon office (503) 430-1065 Business (503) 430-1285 Fax http://www.teraspeed.com This e-mail contains proprietary and confidential intellectual property of Teraspeed Consulting Group LLC ------------------------------------------------------------------------------------------------------ Teraspeed(R) is the registered service mark of Teraspeed Consulting Group LLC ------------------------------------------------------------------ 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 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