Hi All, When we talk about high edge rate signals, we talk about two terms namely 1> 3 dB frequency, which is related to the edge rate as approximately 0.35/Tr and 2> Knee frequency (mentioned in Howard Johnson's famous book and many SI-list mails) which is given as 0.5/Tr. Questions: 1> What is Knee frequency? Does it relate to the highest harmonic present in the signal with significant energy? How relevant it is in High speed board design as against 3dB frequency? 2> To determine the decoupling caps, we have to determine the highest significant frequency involved in the switching signals. Now the question is should we consider the 3dB frequency ( mentioned in High Speed Digital Design by Stephen Hall) or the knee frequency ( in Howards Johnson's Black MAgic) as the best approximation? Let us consider Tr=1ns. Then we have 3dB frequency = 350Mhz and Knee frequency = 500 Mhz. Regards, Anand. ------------------------------------------------------------------ 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