Hi suresh, For your situation the supply coming from FPGA board should be = connected to the digital supply of the second (a/d) board.=20 Reason is obviously the same for which we isolate digital and analog = circuit supplies. Digital circuit contains fast switching circuits and fast transients on power nets are produced. Also a phenomenon called ground bounce is common in digital circuits and we need to stop these = transients from going in analog word because analog circuit has no thresholds and = even a small noise can be amplified and generate the erronoious/noisy = outputs. So as per my opinion you should tie your FPGA boards supply to the = digital supply of 2nd baord and isolate all the analog using filter/bead. Tayyab -----Original Message----- From: suresh [mailto:sureshkumar.v@xxxxxxxxxxxxxxxxxx] Sent: Saturday, May 15, 2004 1:07 PM To: si-list@xxxxxxxxxxxxx Subject: [SI-LIST] Analog&Digital Power planes Hello SI Experts :: =A0 We have three PCb cards in our system.The first one is a FPGA board = and the second board is a analog front end card and contains a)D to A=20 converters b)A to D converters and the third board is a RF Transceiver=20 board.The "D to A" coverter gives input to the RF board and the "A to = D" converter gets its inputs from the RF card. =A0 The power supply to the second board is given from the first board.Now on=20 the second board the power planes are split into two planes a) Analog=20 supply plane and 2)Digital supply plane.Both the planes are joined at a single point through a RF beed. =A0 similarly the grounds are also split into two planes and joined at a single=20 point. =A0 QUEST::The power supply comming from the FPGA card needs to be taken as = Digital power or the Analog power for the second card.Can somebody pls try=20 and reason it out. =A0 Best Regards --=20 suresh - ------------------------------------------------------------------ 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 FAQ wiki page is located at: http://si-list.org/wiki/wiki.pl?Si-List_FAQ 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 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 FAQ wiki page is located at: http://si-list.org/wiki/wiki.pl?Si-List_FAQ 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