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

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From: Doug Brooks (doug@eskimo.com)
Date: Tue May 30 2000 - 14:58:29 PDT


It seems to me (by theory and also by inspection of a wave form) the
highest order harmonics are those that enable the 10%-90% rise time. The
rounded corners at the top and bottom (0%-10% and 90%-100%) are actually
much slower.

I think it is important to qualify the formula
BW=.35/Tr
as the bandwidth up to the 3dB point.
I don't argue with the definition, it's just that others may prefer a
different definition. Or, worse yet, may be thinking in terms of a
different definition without realizing it!
Nevertheless, given that qualification, the derivation is simple and tight.

Again, just my 2 cents:

Doug

At 02:06 PM 5/30/00 -0700, you wrote:
>Doug,
>
>That's fine for the risetime of an isolated edge. However, the corners at
>the top and the bottom of the waveform occur only as the result of higher
>order harmonics. If the amplifier cannot pass these harmonics then we can
>get a good timing measurement for a single edge after a long idle period,
>but successive edges of a repetitive waveform distort, and more so as the
>duty cycle varies from 50/50.
>
>Regards,
>
>
>Steve.

.
************************************************************
Doug Brooks' book "Electrical Engineering for the Non-Degreed
Engineer" is now available. See our web site for details.
.
Doug Brooks, President doug@eskimo.com
UltraCAD Design, Inc. http://www.ultracad.com

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