For the most part the capacitor pad is rather short to be considered a significant discontinuity. However when you try to make it a 50 ohm transition you have to open up the planes underneath. Usually there are plenty of ground vias around the cut-up area so the need for extra stitching might be little bit excessive but a safe practice. -----Original Message----- From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] On Behalf Of Balaji G Sent: Monday, November 18, 2013 6:26 PM To: si-list@xxxxxxxxxxxxx Subject: [SI-LIST] reference plane cutout under DC blocking capacitor pads Hi all, I believe reference plane cutouts under the DC blocking capacitor pads for high speed signals help us minimizing the extra capacitance created between pads and planes and reduces the impedance discontinuity. This means that the pad should refer the farther ground/power as reference (20 mils away from signal layer). Is that means we need to engineer the layers under the cutouts? Say we should move the traces away which are going under the cutout region in the signal layer directly under high speed reference plane. Also, in certain application notes, I got to look at a recommendation of adding ground stitching vias near the pads to provide current return path. If the signals are high speed (12Gbps), I believe the returns would prefer to take a loop around the cutout region in the immediate reference plane rather taking a loop through the ground stitching vias. Can you provide your thoughts on this? Regards, Balaji ------------------------------------------------------------------ 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 forum is accessible at: http://tech.groups.yahoo.com/group/si-list List archives are viewable at: //www.freelists.org/archives/si-list 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 forum is accessible at: http://tech.groups.yahoo.com/group/si-list List archives are viewable at: //www.freelists.org/archives/si-list Old (prior to June 6, 2001) list archives are viewable at: http://www.qsl.net/wb6tpu