******************************************************** Sorry for spamming, folks ... I just realized my mailer is against me today. Arrrrghhh! Netscape !! Thanks Gerald for pointing out. Re-transmission follows: ********************************************************************** Paul, I do not understand what you are trying to say at all. I thought that the driver, left to itself, will force the return current through one plane. The purpose of the de-cap is to make it return on both the planes, so that the thing looks like a stripline and you get all advantages of it ... or for a microstrip to be able to carry both HL and LH edges effectively with low loop inductance (in case of a S-P-P set up) Simply speaking, without a decoupling capacitor, won't we have one of the planes "out" of the loop path, because the CMOS driver will be "off" for that loop? Could you please elaborate? - Neeraj. Paul Levin wrote: > > Dear Goutham, > > Inductance will force the high frequency components of the return > current to be shared equally by the two planes. The decoupling > capacitance in the vicinity of the driver *should* sort out the return > current and bring it to the correct voltage plane. Plane thickness is > not an issue: At these high frequencies, the skin depth is smaller than > any common copper thickness. > > The low frequency components will flow as one would expect from > voltage and load resistance. > > Intermediate frequency components will be somewhere in between. > The transition occurs in the region where the inductive reactance of > the transmission line overtakes the resistance (bulk or skin as appro- > priate) of the transmission line. If you feel up to some fun math, you > could model this as a four-winding transformer (two windings for the > trace and one for each shield) in series with voltage-dependent R's. > > Paul Levin > Senior Principal Engineer > Logic Innovations > _____________________________ > > Goutham.S@xxxxxxxxxx wrote: > > > Hi, > > > > In a stripline environment, with the signal trace equidistant from a ground > > plane and a power plane, what will the return current path be for a H-L and > > L-H > > transition be? Also what percentage of the return current will flow thro > > the > > ground and power planes, assuming the return current will be ditributed > > between > > the two ref planes. Also the two ref planes are assumed to have equal > > thickness. > > > > Any answers or comments........ > > > > Regards > > Goutham Sabavat > > Force Computers india Pvt Ltd > > > > ------------------------------------------------------------------ > > 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 > -- g i g a b i t s @ m i l l i w a t t s National Semiconductor ------------------------------------------------------------------ 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