[SI-LIST] Re: relation between signal rise time and scope rise time
- From: prasad <hariprasad.palli@xxxxxxxxx>
- To: Tom Dagostino <tom@xxxxxxxxxxxxx>
- Date: Tue, 1 Feb 2011 11:50:12 +0530
hi All,
thank you very much for your comments.
i read some where that Tr= measured risetime = SQRT[(Scope system
risetime)^2 + (DUT risetime)^2], which is valid when its a combination of 2
Gaussian Response filters, but if the Scope is a having Brick wall
response, then i believe the resultant rise time would be which ever is
slower among scope's rise time and signal's rise time.
Please correct.
Thanks,
hari....
On 1 February 2011 11:12, Tom Dagostino <tom@xxxxxxxxxxxxx> wrote:
> 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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