Zhengang, We took v(t) = Inverse FFT (Z(f) x I(f)) to look at the time domain noise. Remember to have both the real and imaginary (or magnitude and phase) portions of Z(f) and I(f) so the coherency of the noise components add or subtract properly when the Inverse FFT is performed. Steve -----Original Message----- From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] On Behalf Of ZHENGGANG CHENG Sent: Saturday, May 24, 2008 5:27 PM To: si-list@xxxxxxxxxxxxx Subject: [SI-LIST] target impedance profile Hi all, It seems many SI engineers are using the method described below to define the target impedance profile for PSD: Z(f) = 0.05*V_DC/I(f) or Z_target=0.05*V_DC/Imax(f) Z(f)---target impedance profile at freq f; Z_target---target impedanace at all freq; 0.05---allowed tolerance; V_DC---power raill; I(f) ---current profile; Imax(f)---max I(f)---generallt 0.5Imax(t). But this setup does not guarantee the overall noise is 5%. All it does is making sure noise at each of the frequency of interest is less than 5%. In time domain, the combined content has the possibility of bigger than 5%. So is there a better way to define target impedance profile? Thanks, Zhenggang Cheng ------------------------------------------------------------------ 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 ------------------------------------------------------------------ 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