Sam, Yes, principally lower Z21 means less noise coupled between the two points. However, keep in mind the definition of impedance: it is voltage out per current in. This means if the point of noise injection is low impedance, you can get very low noise voltage at the point of injection, but may get a much higher voltage at a remote point. A typical example is if you drive an open-terminated quarter-wave transmission line with a square wave, where the fundamental frequency equals the quarter-wave resonance frequency. The input impedance of the quarter-wave transmission line will be very low (zero for ideal losless line) at all harmonics of the square wave, creating very low input voltage. The output voltage, however, may be very big, approaching infinite for lossless line and zero source impedance. In other words the voltage gain V2/V1 can be very big. Regards, Istvan Novak SUN Microsystems Sam M wrote: >Hello all, > > I am confused abt the relation between transfer impedance (say Z12) and > noise coupling between two power rails. if the transfer impedance is less, > does it mean the noise coupling is less between the two power rails? > > > > > > > ------------------------------------------------------------------ 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