HI Sunilm I think that you could control better impedance in some ways: 1) ask to your PCB maker to give you the more parameters about = construction he knows, i.e. dielectric constance AFTER the PCB has been packaged and pressed ...; than perform a more accurate simulation. 2) ask to your PCB maker to guarantee impedance (sure it'll cost a bit = more) 3) if you choose a thicker stackup, with more fr4 between traces and reference plane this'll reflect in making wider traces in order to = obtain the same impedance. In this way you'll obtain a line with more precise characteristics, BUT it has some drowback, one is more difficulties = during the phase of layout! 4) use balanced vias The question about noise is really general but I think that, in order = to reduce noise on boards is important to guarantee optimum GND planes (without moats and bridges ...) NEAR power planes, choose a good = network of capacitors in order to filter the components, not to use buffers at = 100% of theirs capabilities and so on... (as the Grandmother uses to say) I think that at 400MHZ (and 800, 1200, ...) your filtering capacitors = act as inductors. The intrinsic capacitance of your PCB, if you placed GND = planes close to power planes, will work well. Hope this'll help you - pardon my terrible English Giovanni -----Messaggio originale----- Da: sunil Morajkar [mailto:msunil@xxxxxxxxxxxxxxxx] Inviato: luned=EC 24 novembre 2003 10.58 A: si-list@xxxxxxxxxxxxx Oggetto: [SI-LIST] high speed PCB design Hello All, I am in phase of designing the 1394a high speed board = with max operating frequency as 400mhz. In my last revision of the board , there was a issue of noise & impedance matching. how one can control impedance ? how can i reduce the noise on the overall board. Noise level @ 400mhz is around 70-80 mv. how one can select filtering circuit. ? please Suggest regds Sunilm ------------------------------------------------------------------ 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.org List archives are viewable at: =20 //www.freelists.org/archives/si-list or at our remote archives: http://groups.yahoo.com/group/si-list/messages=20 Old (prior to June 6, 2001) list archives are viewable at: http://www.qsl.net/wb6tpu =20 ------------------------------------------------------------------ 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.org 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