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12 and 16-bit oscilloscopes

Discussion in 'Electronic Design' started by Chris Carlen, Dec 13, 2006.

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  1. Chris Carlen

    Chris Carlen Guest

    Hi:

    Picotech seems to be the only supplier of these in low cost <$1500 flavors.

    But they are discontinuing their 16-bit version which had 96dB dynamic
    range:

    http://www.picotech.com/applications/resolution.html

    And there USB based 12-bit versions have 72dB rather than the 80dB of
    the parallel port versions. I expect they will dump the parallel ports
    eventually.

    This is a shame. The 16-bit unit is killer for low frequency/audio
    amplifier testing and general spectrum analysis. The FFT functions on
    8-bit fast DSOs from Tek and Agilent are of limited usefulness due to
    meager 70dB range (with averaging).

    I have been communicating with Pico to try to encourage them to keep the
    16-bit or develop another one. They haven't been very responsive.

    I will email the Cleverscope and notifiy them that they might consider
    filling the opening Pico is leaving.



    --
    Good day!

    ________________________________________
    Christopher R. Carlen
    Principal Laser&Electronics Technologist
    Sandia National Laboratories CA USA

    NOTE, delete texts: "RemoveThis" and
    "BOGUS" from email address to reply.
     
  2. Bob

    Bob Guest

    I wonder if picotech ever fixed the glaring bugs in their software?

    My boss bought a ADC-216 when we needed an 50KHz spectrum analyser.
    I'd seen picotech equipment before and reccommended buying a spectrum
    analyser off ebay instead. When the picotech unit arrived I connected
    it in parallel with a conventional scope and tried it out.

    I found several serious software bugs. I can't remember them all now.
    It has an AC voltmeter function, the spec page claims 1% accuracy. It
    worked ok up to about 10KHz and above that the reading were completly
    wrong. The hardware is just a fast ADC so the PC software did the task
    of adding up the area of the voltage versus time graph.

    A picotech support person reproduced the problems I found and promised
    to send a new version of the software. Months later after a few
    reminders they finally emailed me some software, the same buggy
    software I'd already been supplied with the unit.

    Bob
     
  3. Chris Carlen

    Chris Carlen Guest

    [edit discouraging story]


    Bummer. Now I'm disinclined to buy one.

    Any other experiences out there?



    --
    Good day!

    ________________________________________
    Christopher R. Carlen
    Principal Laser&Electronics Technologist
    Sandia National Laboratories CA USA

    NOTE, delete texts: "RemoveThis" and
    "BOGUS" from email address to reply.
     
  4. SioL

    SioL Guest

    I've purchased and used ADC216 specifically for the dynamic range in fft mode.
    For this purpose it seemed very usefull to me and I was able to troubleshoot
    a few things I could never have done without it.
    Although I can't and did not compare its operation against any other comparable
    unit.

    I admit to not having used it as a scope, analogue scope is a much better
    solution for that.

    SioL
     
  5. Tom Bruhns

    Tom Bruhns Guest

    Well, it won't fit in your "under $1500" budget, but HP/Agilent for
    many years has been making a 23-bit 20Ms/s card. It's not necessarily
    useful to 23 bits, but even by today's standards, the distortion and
    spur performance isn't too shabby, and was certainly cutting-edge when
    it was introduced. And in a stand-alone instrument, the HP/Agilent
    89410, especially those made around 2001 and later, should give you
    pretty nice performance out to 10MHz. I can "see" signals 120dB below
    full scale with a dB or so accuracy with mine, if there aren't also big
    signals that put distortion products on top of them. There are a very
    few spurs that keep you from getting to that low a level at every
    frequency, but they are pretty low amplitude and few in number. (We'd
    all love to have 120dB of spur-and-distortion-free dynamic range in a
    10MHz bandwidth analyzer with general-purpose inputs, but it's not
    likely to happen this year...)

    Cheers,
    Tom
     
  6. Guest

    You can get the HP3562A used for under a grand. It is 14 bits and
    100khz. It has GPIB to offload the data.
     
  7. Tom Bruhns

    Tom Bruhns Guest

    Should note it's 100kHz bandwidth; sampling is faster. Of course, it's
    also BIG and HEAVY (and if something goes wrong inside, it may not be
    easy to fix).
     
  8. Guest

    It has a self-check, which makes the used purchase safer. The big
    advantage to the 3562 is the synchromized sine source. No edge effects,
    i.e. windowing errors. Big? You bet. ;-)
     
  9. Fred Bartoli

    Fred Bartoli Guest

    a écrit :
    I do have a 3563A which is the 16bit that followed the 3562A. Big and
    noisy (fan) but excellent.

    The 3562A has service manuals available but I couldn't find the 3563A ones.
     
  10. Tom Bruhns

    Tom Bruhns Guest

    Gee, Fred, I'm curious where you found a 16 bit 3563A ... ;-)

    Cheers,
    Tom
     
  11. Guest

    Are there 3562 manuals on line?
     
  12. Fred Bartoli

    Fred Bartoli Guest

    a écrit :
    I have them in case you can't find them, but I guess I got them either
    from the agilent web site, either from their ftp.
     
  13. Guest

    ftp://ftp.agilent.com/pub/manuals/
    I found them. Thanks.
     
  14. vasile

    vasile Guest

    Hi Tom,
    Did you have the curiosity of checking exactly the accuracy ?
    Below 100dB is quite difficult to claim 1dB accuracy, even with a
    45.000$ VNA or spectrum analyzer.

    greetings,
    Vasile
     
  15. Tom Bruhns

    Tom Bruhns Guest

    Hi Vasile,

    Well, yes, it was a bit more than idle curiosity. :) The linearity
    of the ones with new ADC boards is generally quite good, noticably
    better than the ones with the older boards, and those weren't bad at
    all. Linearity to that level is not guaranteed, though. As you say,
    it's not trivial to test.

    Cheers,
    Tom
     
  16. joseph2k

    joseph2k Guest

    How about a different approach? semi-pro and pro audio offers some
    interesting prospects, such as 10 channels at 24 bits and 192 ksamples /s.
    requires firewire/1394 or usb2. start with RME/hammerfall please.
     
  17. Tom Bruhns

    Tom Bruhns Guest

    One thing to be a little careful about with cards that are designed to
    digitize audio is that they may use ADCs which indeed output 192k
    samples per second, but which have internal digital filters which will
    NOT allow response beyond 1/4 the output sample rate, or thereabouts.
    If the design of the board has limits in the analog signal path, you
    may be able to bypass that, but it will be difficult to deal with an
    ADC like that. In doing a survey of ADCs for such an application, I
    found more than one that was unacceptable for that reason. I believe a
    few also have highpass filters that would prevent them from going to
    DC, and in any event you might have to hack the software to disable
    such a filter. If you want a highpass, it's nice to do it digitally,
    because you can insure zero offset voltage, and many high-end audio
    ADCs have at least the ability to do it in their digital processing.
    (Practically all audio ADCs these days are delta-sigma type, with a lot
    of digital filtering and decimation going on inside.)

    Cheers,
    Tom
     
  18. Mike Monett

    Mike Monett Guest

    [...snip good info]
    Can you tell us which boards had response to DC?

    Which ones would you recommend for an inexpensive low-end pc scope?

    Regards,

    Mike Monett
     
  19. Tom Bruhns

    Tom Bruhns Guest

    Hi Mike,

    Sorry if I wasn't clear about that. I was doing a survey (and not a
    terribly complete one at that) of high resolution ADC parts that would
    be useful in a digitizer that went to at least 80kHz bandwidth. I
    can't tell you about any of the boards; I don't have info on what ADCs
    they actually used. There may be good reasons to sample audio faster
    than 44.1ks/s, but extending the digitized bandwidth much beyond 20kHz
    is probably not very high on the list.

    Cheers,
    Tom
     
  20. I would love to make a "scope" based on something like the
    AD7660. It's a 24 bit 2.5MHz sigma delta ADC
    <http://www.analog.com/en/prod/0,,AD7760,00.html>.

    I was thinking

    - USB powered
    - buffer data in local SDRAM
    - Hi-speed USB interface
    - local SDRAM chip to buffer samples
    - *all* samples streamed to controller PC
    - PC does post processing for "triggering", averaging, spectrum analysis
     
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