Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: quoted-printable Hello experts, I have a problem that has me totally stumped, so I thought you may have som= e ideas. We have some signal lanes with dc-blocking caps, that run at about= 10ghz. I noticed that the planes had not been cutout underneath the pads o= f these caps, which has obvious issues. I simulated the cap structure in HF= SS to find an optimum cutout size, and rolled it into the next spin of the = board. All of my simulations claim that the new structure should have a hug= e positive influence on the si of these lanes. Unfortunately, when we measu= re the eye, it seems to be about the same, or ever so slightly worse! I did= a tdr on the cards with and without the cutout, and the cutouts definitely= seem to flatten the impedance curve along the trace. I haven't been able t= o do a vna measurement yet because I cannot access one side of the trace. I= have ordered boards with only those caps on them so that I can make this m= easurement, but all the initial data seems to say that the transmission mea= surements will also be better with the cutouts. I was wondering if anyone h= ad some possible explanations as to why the eye would be a little worse, in= almost every measurement (according to sig test), when the impedance is fl= atter. Thanks for your help, Matt Severini Signal Integrity Engineer mseverini@xxxxxxxxxxxx<mailto:mseverini@xxxxxxxxxxxx> (801) 987-7127 [signature_image] This e-mail (and any attachments) is confidential and may be privileged. A= ny unauthorized use, copying, disclosure or dissemination of this communica= tion is prohibited. If you are not the intended recipient, please notify = the sender immediately and delete all copies of the message and its attachm= ents. ------------------------------------------------------------------ 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