# RE: [SI-LIST] : DSO Selection

From: Tom Dagostino ([email protected])
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
[email protected]
503-685-1613

-----Original Message-----
From: [email protected]
[mailto:[email protected]]On Behalf Of Ron Miller
Sent: Monday, February 07, 2000 12:01 PM
To: [email protected]
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

[email protected] wrote:

From: [email protected] TECHNOLOGY on 02/07/2000 01:20 PM
To: [email protected]
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?

Thanks,
Manix Velu.

Encl: Nil.

-oOo-

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Ronald B. Miller  _\\|//_  Signal Integrity Engineer
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