Prev: Digital FM demodulation
Next: normalised cross correlation by FFT
From: PRCalDude on 6 May 2008 08:32
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?
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?
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...


From: Tim Wescott on 6 May 2008 11:44
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
From: Rick Lyons on 7 May 2008 06:12
On Tue, 06 May 2008 07:32:34 -0500, "PRCalDude" <prcaldude(a)gmail.com>
wrote:

>Hi all,

(snipped by Lyons)

>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...

Hi,
To add to Tim Wescott's good comments, please
have a look at:

http://www.analog.com/processors/learning/training/design_techniques.html

You'll be glad you did.

Good Luck,
[-Rick-]
 | 
Pages: 1
Prev: Digital FM demodulation
Next: normalised cross correlation by FFT