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

  • Thread starter Bararontok
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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.
 

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  • #2
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The thread originator is requesting an answer to the question.
 
  • #3
berkeman
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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.
Without more context to the question, the answer is that they are the same.
 
  • #4
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Can you define efficient?
 
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Can you define efficient?
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
 
  • #6
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Which digital signalling method listed in post #1:

-Uses electronics that is less complex and prone to malfunction
DC - Most logic devices are unipolar.

-Is less error prone
One measure of immunity from errors involves the amount of difference between a 1-level and a 0-level. If the difference between the levels for AC and DC transmission is the same, the immunity from errors should be the same.

-Uses less electrical energy
I'm assuming you mean uses less electrical energy for the same bit error rate. I'm not sure there's a difference.

-Can operate at higher data rates
I can't think of any reason there would be a difference. In my experience more efficient signalling methods involve more efficient coding algorithms rather than relying on AC or DC.

DC has the disadvantage of not being able to pass through capacitors or transformers. This may be important if bandpass filters are used to reduce noise.
 
  • #7
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DC has the disadvantage of not being able to pass through capacitors or transformers. This may be important if bandpass filters are used to reduce noise.
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?
 
  • #8
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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.
 
  • #9
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That is correct since the DC bias comes from a constant DC power supply while the fluctuating DC signal is a separate component.
 
  • #10
rcgldr
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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:

http://en.wikipedia.org/wiki/Usb

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:

http://en.wikipedia.org/wiki/RS_232
 
  • #11
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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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