[SI-LIST] Re: TDR- rise time-channel bandwidth and speed
- From: "Hany Fahmy" <hanymhfahmy@xxxxxxxxxxxxxxxxxxx>
- To: <fuyejun@xxxxxxxxx>, <si-list@xxxxxxxxxxxxx>
- Date: Thu, 12 Dec 2013 23:47:00 +0100
Hi Johnny,
Suggest to run ur buffer+PKG into a test-load (Application specific, e.g.,
memory channel I/Os, ..etc.) , capture the waveform at the test-load
(test-load can be as simple as the impedance of your traces), then perform FFT
to find the frequency content of the signal that is gonna run through the
channel --> from the frequency content of the waveform, u can decide the
rise-time to use for ur TDR.
This is a nice document for FFT using Excel if u want to be simple:
http://online.sfsu.edu/jtai/downloads/ENGR%20302/Excel.FFT.pdf
Hany Fahmy
CEO & Chief Consultant Officer
Intelligent Solutions BVBA
hanymhfahmy@xxxxxxxxxxxxxxxxxxx
http://www.intelligentsolutionsbvba.com/
http://www.linkedin.com/pub/hany-fahmy/66/852/b11
Phone: +32471650724
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] On
Behalf Of Tom Dagostino
Sent: Thursday, December 12, 2013 11:35 PM
To: fuyejun@xxxxxxxxx; si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Re: TDR- rise time-channel bandwidth and speed
Johnny
You really want to tailor the speed of the TDR edge to your application.
You could use a 12 psec risetime TDR in a system with 500 psec risetimes from
the ICs. But then you would be seeing detail in the TDR waveforms that will
not affect the real signals on those board traces and wasting time fixing
stuff you don't need to fix. Conversely if you used a filtered risetime of 1
nsec on a system where real world signals are 100 psec and you may have
discontinuities masked by the slow risetime that are important to your
signals.
If you use a TDR that is 3 to 5X faster than the risetimes of the signals that
will use the traces you are characterizing you have likely captured everything
you need to.
Hope this helps.
Tom Dagostino
Teraspeed Labs
9999 SW Wilshire St.
Suite 102
Portland, OR 97225
USA
971-279-5325 Office
971-279-5326 FAX
503-430-1065 Cell
tom@xxxxxxxxxxxxx
www.teraspeed.com
Teraspeed Consulting Group LLC
16 Stormy Brook Road
Falmouth, ME 04105
401-284-1827
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] On
Behalf Of Yejun Fu
Sent: Thursday, December 12, 2013 1:22 PM
To: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] TDR- rise time-channel bandwidth and speed
Seems the more you want to dig and clear the more confuse you will have.
Some one tells me the more sharp rise time the better, it offers more
details that a lower rise time can't provide. someone says they prefer to
have filters to make a lower rise time to do TDR for a differential channel.
I want to know what is the right relation between the speed of signal
running through the channel and the rise time and the bandwidth related to
rise time and channel.
Thanks
Johnny
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