[SI-LIST] Re: Rise time bandwidth relation
- From: olaney@xxxxxxxx
- To: a.ingraham@xxxxxxxx
- Date: Tue, 8 May 2007 11:03:26 -0700
> In the instance of an infinite pole, all pass filter a.k.a coax
cable, I've read that BW ~ .31/Tr (10% to 90%). Can anyone clarify the
origin of THAT number?
Certainly not! Or was that meant as a trick question? An all-pass
response such as a lossless coax cable, would have infinite
bandwidth, so the formula above would be meaningless. Or perhaps you
meant lossy coax with some assumed low-pass response...?
OK, disregarding the perfect coax that I can't find in any catalog, yes
-- I mean the kind that has a non-zero risetime. Cutoff and moding
effects can be ignored, though I'd love to see a formula that includes
it! The mere fact of a cutoff frequency implies that Tr > 0, so even the
"perfect" case can't get there.
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