[SI-LIST] Re: Bandwidth
- From: trigg <trigg@xxxxxxxxxxxxxxxxxxxxxxx>
- To: Ken.Cantrell@xxxxxxxxxxx
- Date: Fri, 21 Sep 2001 00:28:39 +0100
A paragraph in "A HANDBOOK OF BLACK MAGIC" by Howard Johnston and Martin
Graham,
20-80% Rise Time.
This rise time is defined as the difference in time between when a step
responce crosses the 20% threshold and when it reaches 80% of its final value.
Manufacturers wishing to improve the appearance of their specification sheets
sometimes quote a 20-80% rise time, which makes the rise time figures look
faster.
T20-80= T(step at 80%) - T(step at 20%)
The 20-80% rise time hinges on measurments taken at only 2 points on a step
responce.Its principle strength is its ease of aplication.Its principal
weakness is its sensitivity to noise or ringing present at the same points.
Practicaly all measurments in this book are 10-90% the book is intended for
"High speed digital design"
hope this helps.
Trigger
Ken Cantrell wrote:
> Rich,
> I use the 20%-80% value only when confirming the [Ramp] data in the ibis
> file. Other than that I use 10%-90%. Under what conditions have you found
> the 20%-80% more accurate?
> Ken
>
> -----Original Message-----
> From: si-list-bounce@xxxxxxxxxxxxx
> [mailto:si-list-bounce@xxxxxxxxxxxxx]On Behalf Of Rich Peyton
> Sent: Tuesday, September 18, 2001 1:21 PM
> To: si-list@xxxxxxxxxxxxx
> Subject: [SI-LIST] Bandwidth
>
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>
> Hi all,
>
> I have equations for:
>
> a) bandwidth requirement = .361/Risetime.
>
> b) f3dB =.35/Risetime
>
> Are the above for 10% - 90% risetimes?
>
> In reading "Electronic Packaging of High Speed Circuitry" by Konsowski &
> Helland (any comments on book? mine- Good Reading )
>
> it states that you should be using 20% - 80% for high speed signals and
> states equation:
>
> c) 3F = 1/trise (20-80%)
>
> If I use a risetime of 1nsec. into the above equations I get:
>
> a) 361 MHz
>
> b) 350 MHz
>
> c) 1GHz
>
> Does anyone want to shed some light on this and comment on which is best to
> use when running in high speeds. I was taught awhile back ago to use the
> 10% - 90%, but am running allot of info that using the 20% - 80% is more
> accurate.
>
> Thanks to all who reply,
>
> Rich
>
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