>On 2013-12-17, at 19:46, Bil Herd <firstname.lastname@example.org> wrote: >> Cool. I missed the exact problem, I kind of responded more to the question of the behavior of ribbon cables. >It was a very relevant answer! Thank you. >Out of those you wrote about - is there a software you use and would recommend for PCB impedance adjustments? First one I found is at http://www.technick.net/public/code/cp_dpage.php?aiocp_dp=util_pcb_imp_cal culator but it doesn't model a path, just a crossection but will help visualize the baseline. I used to use HSPICE when I didn't want to model a coax or a transmission line as a lump sum but as a length of Capacitor,Inductor,Resistor. HSPICE made a change to their Coax model for me in 92 when I showed it deviated from real life at low frequencies, which points outs that tools are manmade things and not real life. To think of adjusting impedance along the path, basically to counteract things that raise or lower impedance too much, keep visualizing the cross-section. A good appnote from Altera is here http://www.altera.com/literature/an/an224.pdf and http://www.altera.com/literature/an/an315.pdf where they talk more about TDR with some good examples. LVDS example: http://www.altera.com/literature/wp/wp_lvdsboard.pdf I really liked the book http://www.amazon.com/High-Speed-Digital-Design-Handbook/dp/0133957241 when it came out as I was able to point to some of the math in support of my more intuitive understanding of noise and propagation. I have an app note somewhere that has a little demonstration of changing the ground plane around the trace as a signal goes through a series termination resistor, basically as it hits the pad, climbs up onto the resistor, through and back down, you have a ground trace one layer under it that gets wider and skinnier with the result being a smoother transition with little abrupt change in impedance. If I find the app I can send a link, it's a great way to test visualization of a real life problem. Bil -- SD! Message was sent through the cbm-hackers mailing list Message was sent through the cbm-hackers mailing listReceived on 2013-12-17 22:03:04
Archive generated by hypermail 2.2.0.