RE: [SI-LIST] : DSO Selection

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From: Tom Dagostino (tom_dagostino@mentorg.com)
Date: Wed Feb 09 2000 - 14:02:54 PST


Careful, the data rate is one thing but if you need to look at edges they
define a different bandwidth. In scope terms the bandwidth is .35/Tr where
Tr is measured from he 10 to 90% points. For a 350 ps risetime the
bandwidth of the edge is 1 GHz. If you were to use a 1 GHz scope you would
measure almost 500 psec as Tr of this edge or a 40% error. A 5 GHz scope
will display the 350 psec as 357 psec or about a 2 % error. To get less
error use a faster scope.

The displayed risetime is the root of the sum of the squares of the
measurement system (don't forget to include the probe here) and the signal
under test. Errors in risetime will translate into errors in prop delay
measurements. You will likely want 3 to 5 X the bandwidth in the
measurement systems compared to the signal of interest (as defined by its
risetime).

Tom Dagostino
ICX Modeling Group
tom_dagostino@mentor.com
503-685-1613

    -----Original Message-----
    From: owner-si-list@silab.eng.sun.com
[mailto:owner-si-list@silab.eng.sun.com]On Behalf Of Ron Miller
    Sent: Monday, February 07, 2000 12:01 PM
    To: si-list@silab.eng.sun.com
    Subject: Re: [SI-LIST] : DSO Selection

    If the data rate is 500 mbs, the maximum frequency is 250 mhz.
    However, to get a good picture of the waveform, 3X or 5X or even 7X the
    max frequency is required(odd harmonic content). 5X 250 would yield
    1.25 Ghz and should give reasonable results.

    Ron Miller

    manix@notes.shuttletech.co.in wrote:

        From: Manickavelu@SHUTTLE TECHNOLOGY on 02/07/2000 01:20 PM
        To: si-list@silab.eng.sun.com
        cc:
        Subject: DSO Selection

        Dear All,

        We are in the process of selecting a Digital Storage Oscilloscope.
The
        signal rate we are interested in is from DC to 500MHz.

        The theory is to choose a DSO that has a bandwidth of 5 times the
rate of
        signal and a sampling rate of 2.5 times the rate of signal.

        But in practical, we are able to measure a 100-MHz signal with a
200-MHz
        bandwaidth DSO.

        So, can we choose a twice BW, and Sampling rate DSO to measure a
500-MHz
        signal?

        Your suggestions and comments would be greatly helpful.

        Thanks,
        Manix Velu.

        Encl: Nil.

                                           -oOo-

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--
Ronald B. Miller  _\\|//_  Signal Integrity Engineer
(408)487-8017    (' 0-0 ') fax(408)487-8017
     ==========0000-(_)0000===========
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