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Digital Delta-Sigma DAC

Discussion in 'Electronic Basics' started by Davy, Jan 17, 2006.

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  1. Davy

    Davy Guest

    Hi all,

    I want to design a digital delta-sigma DAC. It includes a pulse density
    modulated module and RC low-pass filter.

    The pulse density modulated module is a Delta-Sigma type (one adder and
    one substractor). But why use Delta-Sigma type (i.e. how to understand
    it)? Is there any good tutorial on digital Delta-Sigma?

    Best regards,
    Davy
     
  2. Randy Yates

    Randy Yates Guest

    Wikopedia has some good information. At least yesterday it did.
    --
    % Randy Yates % "How's life on earth?
    %% Fuquay-Varina, NC % ... What is it worth?"
    %%% 919-577-9882 % 'Mission (A World Record)',
    %%%% <> % *A New World Record*, ELO
    http://home.earthlink.net/~yatescr
     
  3. Jim Thomas

    Jim Thomas Guest

    Hi Randy,

    You mean "Wikipedia" - replace the 'o' with an 'i'.
    http://wikipedia.org
     
  4. Randy Yates

    Randy Yates Guest

    Ayup. Of that's the way you spell ot.

    :)

    --RY
     
  5. Guest

    Guest Guest

    : Hi all,

    : I want to design a digital delta-sigma DAC. It includes a pulse density
    : modulated module and RC low-pass filter.

    : The pulse density modulated module is a Delta-Sigma type (one adder and
    : one substractor). But why use Delta-Sigma type (i.e. how to understand
    : it)? Is there any good tutorial on digital Delta-Sigma?

    : Best regards,
    : Davy

    Read, read, read!

    In any A/D or D/A circuit there is a quantizer -- the part of the
    circuit that actually does the conversion from analog to digital. The
    error in quantization shows up as noise in the resulting signal. The
    total power of this quantization noise only depends upon the number of
    levels in the quantizer, for any type of data converter (This is often
    stated as the distance between levels, which means pretty much the same
    thing.)

    In a nutshell, while most types of data converters result in
    quantization noise with a white spectrum (i.e. spread evenly throughout
    the signal band,) Delta-Sigma converters "shape" the noise, to move it out
    of the band of interest. This is often combined with oversampling which
    has at least two advantages -- to spread the quantization noise out over a
    larger band (even without noise shaping,) and to be able to move the
    quantization noise far away from the band of interest, such that it can be
    subsequently filtered out relatively easily.

    Delta-Sigma modulation allowed for parctical A/D and D/A
    converters to be built that use as few as 2 levels (i.e. "1-bit
    converters") and have acceptable performance for data conversion of
    relatively low-bandwidth signals like audio (or slower) signals. The
    reason why Delta-Sigma converters are usually used for low-bandwidth
    signals is because the oversampling ratio must be relatively high
    (around 100X) for good performance, which dictates how fast the system
    clock needs to run.

    Joe
     
  6. I would recommend books from the authors Richard Schreier, Gabor C. Temes,
    Steven R. Norsworthy and James C. Candy. Specifically the following books
    cover almost all subjects from end to other:

    R. Schreier, G. Temes, "Understanding Delta-Sigma Data Converters", 2004
    http://www.amazon.com/gp/product/0471465852/103-2515440-5710236
    Very good introduction to the principles, with many examples. A more
    hands-on approach than many other books on the subject.

    R. Schreier, G. Temes, S. Norsworthy "Delta Sigma Data Converters: Theory,
    Design and Simulation", 1996
    http://www.amazon.com/gp/product/0780310454/103-2515440-5710236
    Very detailed and in-depth coverage with good theoretical background on most
    subjects.

    James C. Candy, Gabor C. Temes, "Oversampling Delta-Sigma Data Converters:
    Theory, Design and Simulation", 1991
    http://www.amazon.com/gp/product/0879422858/103-2515440-5710236
    A collection of important scientific papers that covers the full (almost)
    history of the development of this particular field of science. Very good
    supplement for the two other books.

    I have read several other books on the subject, but none of them have the
    accuracy of these books. I would recommend not reading them cronologically,
    but start with the newest one, and then progress to the older books if you
    have a need for more background info or explanation of the theories.

    -Thomas
     
  7. Davy

    Davy Guest

    Hi,

    Thank you for your help!

    I just want to learn the simplest one-bit Sigma Delta DAC.

    And I found a link interesting:
    http://www.embedded.com/shared/printableArticle.jhtml?articleID=22101730

    I have one more question:
    If I want the one-bit Sigma Delta DAC have better performance, shall I
    accelerate the integrator (move the frequency Fs to higher frequency)?

    Best regards,
    Davy
     
  8. Guest

    Hi,

    If you want to understand more about internals of ADC/DAC with
    differentiation of various methods
    I will refer one book

    It titles something like Designing Methods of ADC/DAC from an author
    named Joshpher...

    I am very sorry that I am not able to give correct name of both book
    and author but what ever I knew I have told I had referred this book
    some time back.

    But for delta sigma type of conversion you have to limit the data width
    also as you increase the data width for more resolution the noise will
    cause problems.

    Thanks,
    Regards,
    Kedar
     
  9. Guest

    Guest Guest

    : Hi,

    : Thank you for your help!

    : I just want to learn the simplest one-bit Sigma Delta DAC.

    : And I found a link interesting:
    : http://www.embedded.com/shared/printableArticle.jhtml?articleID=22101730

    : I have one more question:
    : If I want the one-bit Sigma Delta DAC have better performance, shall I
    : accelerate the integrator (move the frequency Fs to higher frequency)?

    : Best regards,
    : Davy

    Yes, that is one way to achieve slightly higher performance.

    Joe
     
  10. Randy Yates

    Randy Yates Guest

    You can read the presentation I made at the comp.dsp conference on
    delta sigma conversion here:

    http://www.digitalsignallabs.com/presentation.pdf

    See especially Figure 9 on page 18, which shows how SNR is related to
    modulator order and oversampling ratio.
    --
    % Randy Yates % "...the answer lies within your soul
    %% Fuquay-Varina, NC % 'cause no one knows which side
    %%% 919-577-9882 % the coin will fall."
    %%%% <> % 'Big Wheels', *Out of the Blue*, ELO
    http://home.earthlink.net/~yatescr
     
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