[SI-LIST] Re: relation between signal rise time and scope risetime
- From: tom@xxxxxxxxxxxxx
- To: "Traa, Boris" <boris.traa@xxxxxxxxxxx>, si-list-bounce@xxxxxxxxxxxxx, "'Alfred Lee'" <alfred1520list@xxxxxxxxx>, "si-list@xxxxxxxxxxxxx" <si-list@xxxxxxxxxxxxx>
- Date: Tue, 1 Feb 2011 17:12:43 +0000
The math I've gone through was for a 2 pole critically damped Gaussian response
Tom
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-----Original Message-----
From: "Traa, Boris" <boris.traa@xxxxxxxxxxx>
Sender: si-list-bounce@xxxxxxxxxxxxx
Date: Tue, 1 Feb 2011 09:31:25
To: Tom Dagostino<tom@xxxxxxxxxxxxx>; 'Alfred Lee'<alfred1520list@xxxxxxxxx>;
si-list@xxxxxxxxxxxxx<si-list@xxxxxxxxxxxxx>
Subject: [SI-LIST] Re: relation between signal rise time and scope rise
time
Dear Tom,
I assume your calculation is only valid if the input of the oscilloscope is a
first order circuit (i.e. the oscilloscope behaves as a first order system). I
once determined the transfer of an oscilloscope and had to conclude that it was
not a first order system.
Kind regards
Boris Traa
System design engineer EMC
It's the currents that make circuits work or fail.
Philips Applied Technologies/EMC center
Room 2.020
High Tech Campus 26
5656AE Eindhoven, The Netherlands
Tel: ++ 31 40 27 43766
Fax: ++ 31 40 27 42224
E-mail: boris.traa@xxxxxxxxxxx
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] On
Behalf Of Tom Dagostino
Sent: 2011 Feb 01 6:43 AM
To: 'Alfred Lee'; si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Re: relation between signal rise time and scope rise time
It all depends on how accurate you want your measurements to be. You can do
the math yourself by remembering that the measured risetime = SQRT[(Scope
system risetime)^2 + (DUT risetime)^2]. The scope system includes the scope
plus probe plus whatever is between the scope and the DUT.
If DUT and scope have the same risetime the error will be 41.4% If the scope
is half the DUT the error is 11.8%. At one forth the risetime you are down to
3% and at 5 times faster you have 2% error when measuring from the scope screen.
Tom Dagostino
Teraspeed Labs
13610 SW Harness Lane
Beaverton, OR 97008
503-430-1065
tom@xxxxxxxxxxxxx
www.teraspeed.com
Teraspeed Consulting Group LLC
121 North River Drive
Narragansett, RI 02882
401-284-1827
www.teraspeed.com
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] On
Behalf Of Alfred Lee
Sent: Monday, January 31, 2011 9:20 PM
To: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Re: relation between signal rise time and scope rise time
Here's my take.
With HJ's rule, at near the limit, what you see is not what you get, but you
could figured out what it was.
With Tek's rule, who is in the interest of selling scopes, at the limit, what
you see is for all practical purposes what you get.
-
Alfred
"prasad" <hariprasad.palli@xxxxxxxxx> wrote:
>hi All,
>i was going through one of the note from an oscilloscope vendor saying
>
>*oscilloscope rise time < signal rise time/5.* its available at link
>below
>http://www.tek.com/Measurement/scopes/selection/pdf/55W_13768_2_rise.pdf
>
>
>but when i looked at the howard Johnson's book for High speed Digital
>Design, where the BW of a signal is calculated as FKnee= .5/Tr, and
>then
>BW of scope is chosen as around 1.4 to 2 times of BW.
>
>am i missing anything while trying to interpret what the above
>highlighted
>statment? request your comments.
>
>
>Thanks for taking time to read this....
>
>
>
>Best Regards,
>Hari....
>
>
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