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1% 8 bit R2R DAC @ 44KHz = Joke?

Discussion in 'Electronic Design' started by [email protected], May 19, 2006.

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  1. Guest

    I'm trying to make a stereo audio playback device with a frequency
    response up to 20khz. I am feeding 16 bits of digital PCM audio into a
    16bit shift register which has a storage latch, and then latching the
    output into an 8-bit R2R DAC in 100ns. The R2R dac is discrete, i.e. a
    bunch of resistors tied together with a buffer opamp. I'm wondering how
    imprecision in the resistor values (they will be 1% tolerance) affects
    the output? I.e. if I looked at the FFT of the original and the FFT of
    the output, what differences would I see? (ignoring quantization
  2. Joerg

    Joerg Guest

    Archie Bunker would have said "louseh". For audio eight bits ain't much
    to write home about. Imagine that the MSB resistor is 1% off. That's
    already about twice as much as the contribution of the LSB resistor.

    You could measure them all out and put a correction LUT in. Or use
    precision resistors or better yet a "real" DAC.

    Regards, Joerg
  3. Luhan

    Luhan Guest


    As long as you are shifting out your data anyway ... try a phillips
    TDA1312 16-bit stereo DAC.

  4. Ben Jackson

    Ben Jackson Guest

    FWIW, you can get little SOT DACs from Analog Devices like AD5300,
    AD5301. They also have pin- and protocol-compatible 10 and 12 bit
    versions (probably higher, too, but I haven't looked at them).
  5. Jim Thompson

    Jim Thompson Guest

    Back some 40 years ago, when 16-bit DAC's were horribly expensive, I
    demonstrated a system that had 8-bits of resolution plus 8-bits of

    It was for the (IIRC) L-1011 aircraft passenger audio system.

    Sounded great!

    They chose instead to pay thru the nose and went with 16-bit DAC's :-(

    ...Jim Thompson
  6. Genome

    Genome Guest

    Oh, shut up... That was just after WWI when people were converting Avro's
    for trips to the seaside. America hadn't even been invented and you're
    babbling on about how you designed the tampon!

  7. Joerg

    Joerg Guest

    Hello Jim,
    Maybe the stuff I did was similar. 8-bit DAC, feedback and another 8-bit
    DAC of same breed as a "modulator". If that's the same you'd hold the
    title since I was still swinging from trees 40 years ago.

    16-bit in a Lockheed? Somehow that doesn't seem to make much sense.

    That is sad. Did they think you were too young?

    Regards, Joerg
  8. Jim Thompson

    Jim Thompson Guest

    Precisely (both sentences ;-)
    That's what they wanted. I always liked the 1011... don't know why it
    faded away so quickly.
    Probably, I was only 26 ;-)

    Gawd! I feel old now!

    ...Jim Thompson
  9. Jim Thompson

    Jim Thompson Guest

    If Al Gore invented the Internet, _I_ invented the tampon ;-)

    ...Jim Thompson
  10. Genome

    Genome Guest

    I don't see how A1 Gore and the internet are related. How do flat hedgehogs
    come into this? I might see the tampon link but I wouldn't want one in mine.
    Perhaps it's a cultural thing....

  11. Joerg

    Joerg Guest

    Hello Jim,

    The Tristar is a great aircraft, huge. They didn't fade, LTU (the
    tourist branch of Lufthansa) used lots of them. I wouldn't be surprised
    if they still do. Once my wife and I had the pleasure to hop on a ferry
    ride from Dublin to Shannon. Just imagine, about 20 passengers in a
    1011. "Take any seat you want" the stewardess from Air Caledonian said.
    That's about how old I was when I did the DAC trick. Had to, because
    anything else was very expensive since this was RF stuff.

    Nah, my great-grandpa hopped on a motorcycle at 95. He didn't understand
    our worries. "But I had to buy some new shoes".

    Regards, Joerg
  12. Did you use it?

  13. Jim Thompson

    Jim Thompson Guest

    Yep. Shoved it up the ass of a leftist weenie ;-)

    ...Jim Thompson
  14. Jim Thompson

    Jim Thompson Guest

    I did one last year that was linear in dB's... at 500MHz.
    I thought you were going to say "underwear" ;-)

    ...Jim Thompson
  15. Genome

    Genome Guest

    With or without the hedgehog?

  16. Jim Thompson

    Jim Thompson Guest

    Special coarse wood rasp texture ;-)

    ...Jim Thompson
  17. Did you need any duct tape? ;-P
  18. Rich Grise

    Rich Grise Guest

    That's what they wanted. I always liked the 1011... don't know why it
    faded away so quickly.

    Wasn't that the one that they nicknamed "the swamp buggy", because
    they kept crashing in the Everglades or something?

  19. Rich Grise

    Rich Grise Guest

    I was on a 747 ride like that once - about a half-dozen of us went
    upstairs to the lounge and sat on the floor and played cards. :)

  20. JeffM

    JeffM Guest

    Just the once--and it was stupid humans that caused it
    (the aircraft commander didn't delegate responsibilities properly).
    The airplane was only fractionally to blame.
    (I have never felt more safe flying than in a TriStar.)

    The one that sticks in my mind
    is the burned-out ass end on the end of the runway at DFW.
    (The impetus for all the Doppler-shift radar we have now.)
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