Slightly OT: What good does oversampling provide in an oscilloscope?

If I have a digital oscilloscope that has, say, a 1GHz bandwidth, presumably I need to sample the input signal at something above 2Gsps if I want to capture all the information present in the signal -- say 2.5Gsps given the anti-alias filters I might be able to realistically build.

I see, though, that something like a Tektronix DPO4104 actually samples at

5Gsps. I understand how that can buy them another 6dB SNR (from noise reduction), but other than this... does oversampling buy you anything on a DSO?

Does anyone out there prefer a classic analog scope like a Tek 2465B over a

*modern* DSO (one that uses color or intensity variation to tell you something about how the signal spends most of its time, like the brightness on an analog scope does -- the old DSOs just plotted min & max voltages sampled at each pixel...)?

---Joel

Reply to
Joel Kolstad
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Joel, I'm not done with the article, so you'll have to wait for the long answer.

The short answer is that Nyquist is a _theoretical_ limit, in practice you usually need to go way above Nyquist or you need one big filter. If you do use one big filter then you cut off way sharper than the

6dB/decade dominant pole that you see in most O-scopes.

I suspect the oversampling is there so they can have a mild slope, at least at first, in their anti-aliasing filters.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

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Reply to
Tim Wescott

Always when I'm measuring noises. The Nyquist effect is still there even you have a very good antialising filter.

greetings, Vasile Surducan

Reply to
vsurducan

_What_ anti-aliasing filters?

Cheers,

Phil Hobbs

Reply to
Phil Hobbs

Hi Phil,

It had occurred to me that... hmm... building a DC-1GHz lowpass filter that's reasonably flat is probably somewhat challenging... but you're saying many a DSO doesn't have any AAF, eh? Interesting...

Reply to
Joel Kolstad

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