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adaptive sampling frequency

Discussion in 'Electronic Design' started by mustafa umut sarac, Jul 14, 2006.

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  1. Hello , I was reading headwise site and I learned that sampling is not
    a good working method. I will not go to wobbling , windowing details.
    but i thought is it possible to change samplling signal adaptive to
    recording signal. analog signal could drive the sampler .

    What do you think ?

    Regards ,

    Mustafa Umut Sarac
     
  2. I think you're nuts.
     
  3. John Larkin

    John Larkin Guest

    That's an idiotic statement, at the very least.


    Last week Cornell sent me an email offering to license an invention
    that digitizes a signal only when the level crosses bit boundaries, so
    it outputs low rate samples when the signal isn't changing much.

    Seems sort of silly to me, given real-world issues like noise and
    signal processing.

    John
     
  4. Luhan

    Luhan Guest

    Sounds like a compression algorithm to me. Some of them Do work, but
    this is no breakthru idea.

    Luhan
     
  5. John Larkin

    John Larkin Guest

    No, it's actually in the adc itself. It's like a classic flash with,
    say, 1023 comparators, each comparing the input against taps on a
    resistive divider. They just don't do anything until one of the
    comparators transitions, or something like that.

    Looks like I deleted the email.

    John
     
  6. PeteS

    PeteS Guest

    But that's merely a form of adaptive sampling by adapting the sampler
    rather than compressing afterwards (and yes, a form of compression)
    which has been around for decades. I remember talking to a few friends
    about sampling and not bothering to sample unless there was a change in
    the input at least 20 years ago. (I still have the notes from those
    meetings)

    Cheers

    PeteS
     
  7. John Larkin

    John Larkin Guest

    Then your notes may invalidate the Cornell patent.

    John
     
  8. Guest

    The patent isn't worth anything - I used that technique when I
    programmed the PDP-8 to handle the experimental data for my Ph.D. work.
    I knew I was looking at a monotonic decay, so I had the computer sample
    the data until there was a significant change in voltage, then work
    out the average value of all the samples stored since the last value
    had been stored, then store that average (and the time) if there had
    been a siginficant change in voltage.

    The initial samples were summed over 2^n intervals (double precision)
    and divided by 2^n by shifting., which dealt with the noise. I adjusted
    n by hand, but a high pass filter would have extracted the noise to
    allow "n"to be set automatically.

    Much the same idea was employed in the Cambridge Instruments Electron
    Beam Tester 1989-91, but it wouldn't be useful in a patent case, since
    it wasn't publicly documented.
    The digital signal processing was all done in 100k ECL, and all the
    sample intervals were restricted powers of two to avoid the necessity
    for a proper multiplier.

    Worked fine in both application - and in 1968 it meant that I could get
    my data into the 3k of 12-bit memory left available after I'd loaded my
    900-word program. Ph.D. was deposited in the Melbourne Univeristy
    library in 1970, so Cornell's patent is probably so much waste paper.
     
  9. PeteS

    PeteS Guest

    Well, Bill's stuff is certainly more impressive, but it would be
    amusing if you mentioned it to Cornell the next time they ask you to
    license this 'astounding' invention ;)


    The details:

    First meeting: May 7 1983
    Discussion on reducing hardware and software requirements for the
    experimental voice encoder [back then, of course, memory was at a real
    premium as you remember]. We used a power supply for basic encoding
    simply because we could read it with a scope to correlate (at least
    roughly) with the data for proof of concept.

    Sampled data : Power supply under varying loads to prove the principle
    of the project

    Issue: fixed sampling takes too much memory

    Possible resolution:

    "As the supply only changes significantly when the load changes, set
    the circuitry to trigger a comparator when the input changes
    significantly enough to require a sample. So the output may be
    reconstructed, tag a new sample (where sampling has been suspended)
    with the sample frame ID."

    Those are my raw notes. There are also schematics (included a sampler
    counter so the sampler count could be tagged at the start of a new
    sample sequence). Takes me back.I'll need to dig out at least three
    notebooks to reconstruct the whole thing, but I have no doubt I could
    :)

    Cheers

    PeteS
     
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