# Re: [SI-LIST] : RE: Split Plane

From: greg kimball ([email protected])
Date: Tue May 30 2000 - 22:16:08 PDT

Doug et al-
Has anyone extended the '0.35' rule beyond single-order systems?
Terman's
with overshoots in the 10% range - but doesn't reference any derivation.
I'd be curious about high Q networks up to 50% for ex.
Anyone?
Regards,
Greg Kimball
Apps Engr
TI Storage Products GP

Doug Brooks wrote:
>
> My 2 cents worth:
>
> I'm not sure there IS a derivation of the .35/Tr=BW equation.
>
> Here is a different, simplistic, but intuitive way to look at it. Look at
> the rise time of the fastest signal you have. It (closely) resembles the
> rise time of a sine wave. Superimpose a sine wave over that rise time so
> that the rising edges are congruent. The frequency of a sine wave that has
> the same rise time as the rise time of your signal is approximately
> .3/Tr. (That is because the rise time of a sine wave is approximately 30%
> of its period!) That is the maximum frequency you need to be able to pass
> in order to pass the rise time of your signal.
>
> Hence, BW is (approx) .3/Tr,
> sometimes expressed as .35/Tr
> other times expresser as 1/Pi*Tr (Pi = 3.14159...)
> and then sometimes approximated by other ratios close to these, perhaps
> allowing for a fudge factor.
>
> Doug Brooks
>
> At 09:55 AM 5/30/00 -0700, you wrote:
> >The equation for bandwidth .35/Tr = BW assumes a critically damped Guassian
> >response and 10% to 90% Tr times. Different filters (responses) will have
> >different constants. For example, if the response of the filter is a simple
> >RC filter the bandwidth will be .4545/Tr.
>
> .
> ************************************************************
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> .
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>
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