Hello Guys, I have this confusion regarding "*Return currents*"- 1) In the paper "SSN & power plane bounce in CMOS technology" by Larry Smith ( http://www.csee.umbc.edu/vlsi/reports/ssn_pwr_planes.pdf <http://www.csee.umbc.edu/vlsi/reports/ssn_pwr_planes.pdf+>). This is available online for free, so i m pasting it here. (I hope i can) In the following excerpt- "Suppose the transition is from low to high and the cross-section of the package has the transmission line located above a Vdd plane as shown in figure 1.The driver connects the Vdd plane to the transmission line through a low impedance.Current flows from the Vdd plane onto the transmission line which is low, say ground potential.As the wave front propagates down the transmission line, charge flows into the capacitance between the trace and the Vdd plane, raising the potential on the trace up to Vdd. The current path is complete because charge from the Vdd plane flows in a complete loop from the Vdd plane, through the driver and onto the transmission line that is referenced to the Vdd plane. If there is a ground plane underneath the Vdd plane, it is not disturbed because it is not part of the current loop." Where does the return current flow? Does the return current flow through the inter-plane capacitance? Doesn't it need to flow thru a reference plane? If it can't flow thru the Gnd plane, is it possible for it to flow thru the same power plane which is supplying the current (i hope not coz it will totally screw my fundamentals on current flow). 2)What if the package does not have an explicit power or ground plane i.e. Power & Gnd are normal, thin traces (like other signal traces), distributed sporadically along with other I/Os, signal, clock traces etc. (Although the power & ground traces are de-coupled inside the chip & if the I/O traces r driven using a CMOS buffer) How is the return current going to flow now, when the I/O traces r driven using the buffer? Will the return current still look to flow through the nearest Power or Gnd reference trace it finds, given they are randomly routed in the package like ordinary traces? I'd really appreciate if somebody can clear this nagging doubt. Thanx in advance. Regards, pras ------------------------------------------------------------------ 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