Re: Understanding high speed digitizer parameters

On Tue, 06 May 2008 07:32:34 -0500, PRCalDude wrote:

Hi all,

I'm new to this board and need some steering in the right direction.

I've been trying to understand spec sheets for high speed digitizers
and
had several questions:

1. What does "form factor" tell you?

Usually that means the physical form of the card; it's often taken to
mean what the card is compatible with (ISA, VME, etc).

2. What is the relationship
between MSPS (mega samples/s) and bandwidth? For example, I saw one
card
that touted a 250 MHz BW, but only supported 105 MSPS signal capture
rate. Shouldn't the signal capture rate be much higher?

Not necessarily. You're assuming that the card should do anti-aliasing.

But if you're going to use the card to sub-sample bandlimited data (as is

done in radios) or to sample non-stationary or non-Gaussian data with
high signal-to-noise ratios then you want the most bandwidth you can
get. I have a paper that touches on this: http://www.wescottdesign.com/
articles/Sampling/sampling.html.

Note that the sampler's window duration and jitter performance will limit

a data acquisition system's high-frequency performance just as easily as

the bandwidth will. Since these specifications will be buried (or
nonexistent), and possibly hard to interpret, you'll have to dig for
them.

3. Does anyone have a link where I can read up on all of this myself?
The standard DSP books don't seem too helpful...

Not that I know of, although hopeful titles would be like "analog to
digital conversion applications" or "data acquisition applications". If

there is a book I'd like to hear about it; in the mean time this is
something that one absorbs with experience (and by asking questions in
newsgroups).

"Standard DSP" books teach theory, and do so very well. _Applying_ the
theory is left as an exercise to the reader.

--
Tim Wescott
Control systems and communications consulting
http://www.wescottdesign.com

Need to learn how to apply control theory in your embedded system?
"Applied Control Theory for Embedded Systems" by Tim Wescott
Elsevier/Newnes, http://www.wescottdesign.com/actfes/actfes.html

Mark, Tim,

Thanks a lot.

Tim,

I'll try to digest some of your papers and then post some follow up
questions on this thread.
.

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