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...
Understanding high speed digitizer parameters
Started by ●May 6, 2008
Reply by ●May 6, 20082008-05-06
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
Reply by ●May 6, 20082008-05-06
>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...I would recommend any application notes from companies that design A/D converters. Analog Devices, National Semiconductor, Atmel, Maxim, TI, etc., all have good app notes as I recall. I think I've read Tim's papers as well at one time or another. Mark
Reply by ●May 6, 20082008-05-06
>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 digitizersand>> 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 onecard>> 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 forthem.> >> 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.
Reply by ●May 6, 20082008-05-06
Oh, I should add, Pentek (www.pentek.com) has some stuff on their website that may be of interest as well. They would be particularly useful if you're purchasing some sort of receiver board (if you aren't already looking at theirs in particular). I say that because you mentioned "form factor," which implies you may not be delving directly into an ADC itself, but a product that uses an ADC in some fashion. Their stuff tends to be a bit adverty for their own products, but just about any app note is. You get used to that. :) I don't own any stock in Pentek, but I am doing a system design with one of their boards at the moment, hehe. Mark
Reply by ●May 6, 20082008-05-06
PRCalDude wrote:> Hi all,...> I've been trying to understand spec sheets for high speed digitizers and > had several questions:...> The standard DSP books don't seem too helpful...That's because analog-to-digital converters are primarily analog gizmos. You need to be conversant with analog specs to understand them. Data sheets and application notes from (of all people) Analog Devices Inc. can be very helpful. Other makers also produce nifty and informative literature. Jerry -- Engineering is the art of making what you want from things you can get. �����������������������������������������������������������������������
Reply by ●May 7, 20082008-05-07
On Tue, 06 May 2008 07:32:34 -0500, "PRCalDude" <prcaldude@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-]
Reply by ●May 7, 20082008-05-07
>On Tue, 06 May 2008 07:32:34 -0500, "PRCalDude" <prcaldude@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-] >THE Rick Lyons answered my message board posting. Thanks Rick!
Reply by ●May 7, 20082008-05-07
PRCalDude wrote:>> On Tue, 06 May 2008 07:32:34 -0500, "PRCalDude" <prcaldude@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-] >> > THE Rick Lyons answered my message board posting. Thanks Rick!He's a good guy all around. He even has good taste in beer! Jerry -- Engineering is the art of making what you want from things you can get. �����������������������������������������������������������������������
Reply by ●May 8, 20082008-05-08
>PRCalDude wrote: >>> On Tue, 06 May 2008 07:32:34 -0500, "PRCalDude" <prcaldude@gmail.com> >>> wrote: >>> >>>> Hi all, >>> (snipped by Lyons) >>> >>>> 3. Does anyone have a link where I can read up on all of thismyself?>>>> 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-] >>> >> THE Rick Lyons answered my message board posting. Thanks Rick! > >He's a good guy all around. He even has good taste in beer! > >Jerry >-- >Engineering is the art of making what you want from things you can get. >����������������������������������������������������������������������� >I love beer myself. I've been drinking a lot of a local IPA lately. Rick, Your link definitely put me on the right track, especially pages 5.17-5.20. I hope this isn't too stupid of a question, but I can use radix-2 FFT benchmarks to estimate 2D FFT processing time, correct? My hunch is 'yes'. One more question on a slightly different note, where do I read up on appropriate use of boards of different form factors? In other words, when do I use a card with a PCI card a VME card, etc and what are their various applications?
