Trust but verify!
Best Regards
Charles Grasso
Compliance Engineer
Echostar Communications
(w) 303-706-5467
(c) 303-204-2974
(t) 3032042974@xxxxxxxxx
(e) charles.grasso@xxxxxxxxxxxx
(e2) chasgrasso@xxxxxxxxx
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] On
Behalf Of L R
Sent: Tuesday, August 18, 2015 3:15 PM
To: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Why do we still TDR pcbs
Hi folks,
See lots of discussion this month on whether SI has become commoditized. I'll
hold off my thoughts on that... and instead ask my
"too-ashamed-to-ask-but-will-ask-anyways" question.
The question is this. Why do we still insist on board impedance data from our
PCB manufacturers?
Here's the rationale behind this question As we all know too well, PCB trace
impedance is not a nice constant real value (say 50 ohms) so we can't really
expect a single number(right?). And with that said, PCB manufactures never
provide us with the details of their measurement (edge rates, launches, ref
planes anyone?). They just give us a number saying they are within 10%. Great.
We know nothing from this other than I can sleep better at night knowing my,
say, single ended clocks will work fine. Well, how useful is all that for links
designed for my fancy 10Gbps or more? Wouldn't it be more useful for them to
give us S11/22?
- Lenny
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