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What type of digital signaling is more efficient, digital DC or digital AC?

  1. Jul 4, 2012 #1
    What type of digital signaling is more efficient, digital DC or digital AC?

    With digital DC, the square-wave signal is only between a (+) value and 0.

    With digital AC, the square-wave signal is between a (+) & (-) value.
  2. jcsd
  3. Jul 10, 2012 #2
    The thread originator is requesting an answer to the question.
  4. Jul 10, 2012 #3


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    Staff: Mentor

    Without more context to the question, the answer is that they are the same.
  5. Jul 10, 2012 #4
    Can you define efficient?
  6. Jul 10, 2012 #5
    Which digital signalling method listed in post #1:

    -Uses electronics that is less complex and prone to malfunction
    -Is less error prone
    -Uses less electrical energy
    -Can operate at higher data rates
  7. Jul 10, 2012 #6
  8. Jul 10, 2012 #7
    What if the DC is a fluctuating DC? A constant DC cannot pass through a capacitor in series because once the capacitor is fully charged, it can no longer permit current flow, but in a fluctuating DC, the capacitor has time to discharge its stored energy when the power is cut off.

    In the case of a transformer, is a fluctuation in current enough for the primary inductor to emit radiation that can be absorbed by the secondary transformer or is a reversal of polarity necessary?
  9. Jul 10, 2012 #8
    With both capacitors and transformers the fluctuation of the DC, which will include both data and noise, will pass through, but the DC bias will not. At that point we can no longer call it a DC transmission method.
  10. Jul 10, 2012 #9
    That is correct since the DC bias comes from a constant DC power supply while the fluctuating DC signal is a separate component.
  11. Jul 10, 2012 #10


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    Homework Helper

    If the orignal post means digital signals used in common integrated circuits, then most logic just uses some positive voltage and zero voltage for the two states. Decades ago, computers like the HP 2100 mini-computer used +5, -2 volts for it's TTL logic on it's circuit boards.

    Interfaces like USB send synchrounous (fixed clock rate) data via a differential pair of signals, +D and -D, where -D is an inversion of +D, each with a 3 volt range. There are also ground and +5 volt pins, which the host drives to send power to some USB devices. Wiki article:


    Interfaces like RS-232 can range from +/- 3 volts to +/- 15 volts, and for the original PC, +/- 12 volts was used for RS-232. There is a ground pin used as a reference for 0 volts. Wik article:

  12. Aug 2, 2012 #11
    Won't the "phase angles" of a sampled A/C become random unless your sample rate is matched to the A/C frequency?
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