Thanks Istvan,
The paper is very nice and detailed.
I agree with you (110%)
Best regards
MN
On Wed, Aug 19, 2015 at 6:38 AM, Istvan Novak <istvan.novak@xxxxxxxxxxx>
wrote:
Lenny,
A respectable PCB fabricator will be able to give you the measurement
setup and procedure how they do their TDR testing.
There are also IPC recommendations for TDR testing of PCB traces;
however, what is not standardized, how long test trace has to be
measured. This, coupled with the fact that the actual trace cross
section may vary some from layer to layer and even more from design to
design, the design-dependent loss-related distortion of the TDR response
makes it challenging to interpret the result. However, it is still a
fast and efficient way of checking manufacturing consistency and
potential lot-to-lot variations. I presume you would know how to
interpret S11/S22 data if you get it, but a lot of customers may not
know how to do it, even if the pcb vendor supplies that data. I guess
these are the main reasons why it is still widely used.
Some of these items were discussed in
http://www.electrical-integrity.com/Paper_download_files/DC13_Determining_PCB_Trace_Impedance.pdf
You may find it useful to look at.
Regards,
Istvan Novak
Oracle
On 8/18/2015 5:15 PM, L R (Redacted sender digitalchkn@yahoo for DMARC)
wrote:
à Hi folks,commoditized. I'll hold off my thoughts on that... and instead ask my
See lots of discussion this monthà on whether SI has become
"too-ashamed-to-ask-but-will-ask-anyways" question.
The question is this. Why do we still insist on board impedance datafrom our PCB manufacturers?
Here's the rationale behind this questionà As we all know too well, PCBtrace impedance is not a nice constant real value (say 50 ohms) so we can't
really expect a single number(right?).à Andà with that said,à PCB
manufactures never provide us with the details of their measurement (edge
rates, launches, ref planes anyone?).Ã They just give us a number saying
they are within 10%.Ã
Great.Ã Ã We know nothing from this other than I can sleep better atnight knowing my, say,Ã single ended clocks will work fine. Well, how
useful is allà that for links designed for my fancy 10Gbps or more?
Wouldn't it be more useful for themà to give us S11/22?à Ã
- Lenny
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