Published by Eric Bogatin on 06 Sep 2012 at 09:04 am
There are two clear trends in all high speed interfaces, such as PCIe, SAS, Infiniband and even DDR memory: data rates are currently in the gigabit regime and there is a roadmap that requires the current data rates to operate at even higher data rates in the next generation.
As we all know, as data rate increases, signal integrity effects get worse and luck goes down.
If you want to get some insight into the design strategies and tactics to manage the transition to the next higher data rate, you’ll want to watch this webinar I moderated in late Aug, 2012. This topic is one of the themes in our new class: Advanced Gigabit Channel Design (AGCD). For more information, check out our web site.
In my role as contributing editor for EDN, in this webinar, I moderated a panel of three industry experts: Jim Nadolny of Samtec, Brad Griffin of Cadence and Allen Tung of NXP. I posed them three questions about the problems, strategies and tactics of higher data rate system design and we discussed the answers.
There were a number of key points that came out. Here is a brief teaser.
Brad Griffin: for shorter time to the correct design, it’s critical to integrate analysis as part of the layout and design flow. This includes not just reflections, cross talk and losses, but also “power aware” analysis.
Allen Tung: USB 3.0 operating at 5 Gbps will see significant eye closure due to the losses in the boards and cables in typical applications. One way of opening eyes and minimizing the impact from the interconnects is adding a re-driver or repeater chip in the signal path, typically placed at the edge of the board. This does not require any changes to the rest of the circuit.
Jim Nadolny: As a good rule of thumb, the eye will probably be sufficiently open with no equalization if the insertion loss at the Nyquist is no more than –7 dB. There should be about 20 dB SNR so the acceptable cross talk should be less than about –25 to –30 dB in this case. Using pre-emphasis only, you can recover an acceptable eye with about –12 dB insertion loss at the Nyquist. And with FIR, CTLE and DFE, you can recover an acceptable eye with about –25 dB insertion loss at the Nyquist.
If you have suggestions for future webinars, drop me a line!