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Analog Forced into Digital

Discussion in 'General Electronics' started by Radium, Nov 14, 2003.

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  1. Radium

    Radium Guest

    What will happen if an sine-wave analog signal is forced into a
    electrical device only meant for receiving digital signals?
  2. Robert Baer

    Robert Baer Guest

    Depends on the amplitude of the sine wave, and hysteresis levels (if
    A few years ago (1980 to be a litle more accurate), the first IBM
    PC/XT has a cassette port that was meant to use the Kansas City standard
    for reading/writing binary data.
    This is a specific case where an analog (audio) signal drove a digital
    input; no hysteresis was used.
    A nifty program was made so one could record voice and music to files,
    and play them back.
    One-bit audio!
    Worked quite well, a lot better than one would expect.
    Just make sure that the input is not over-driven; the positive swing
    should be clamped to prevent it from going more positive than the supply
    voltage of the digital IC that is being driven.
    Most digital ICs already have clamping for negative signals.
  3. Quack

    Quack Guest

    What will happen if an sine-wave analog signal is forced into a
    The 'digital device' will see a '1' or '0' when the analogue signal
    rises above or falls below a curtain threshold. As far as i have seen,
    this is usually about 1.5 to 2.0 volts. below which will be seen as a
    '0', above a '1' (typically).

    What are you trying to do ?

  4. Most likely it will not respond, or may output some noise if anything.
    The digital circuit, depending on its design, should normaly mute if
    it does not recognize the proper protocal structure, such as packet ID
    data, parity, and the proper pulse train of data.

    Jerry Greenberg
  5. Dbowey

    Dbowey Guest

    glucegen posted:
    First it depends on what you mean by "device."

    Do you mean, for example, a modem's digital port (equipment)?

    Do you mean an IC designed for digital applications (component)?

    An analog signal can drive some digital components, but the component must be
    selected to be able to withstand a slow rising voltage. Components that can't
    handle the slow rise-time will likely be damaged.

    At best driving an analog signal into the digital port of some equipment will
    do nothing, or at best result in garbage at the output. Or it could damage a
    component in the equipment.

  6. Radium

    Radium Guest

    How so?
    I don't understand why a device strong enough to handle the roughness
    of digital signals (discrete, square-wave, spikes) could not enjoy the
    smoothness of analog signals (smoothly varying, sine-wave)
  7. Dbowey

    Dbowey Guest

    glucegen posted:
    With a slow rise time signal, the device can be in an indeterminate state
    between 0 and 1 for too long, drawing excess current. Read component specs.

    ..>I don't understand why a device strong enough to handle the roughness
    You are attempting to apply attributes to analog and digital that are not
    realistic. There is nothing "rough" about digital signals.

    In analog, not all signals are sine-waves.

  8. Robert Baer

    Robert Baer Guest

    *If* the input is TTL, then the threshold is 1.4V and varies according
    to temperature (roughly -4.4mV/C).
    CMOS input thresholds are about half of the supply voltage *if* no
    hysteresis; i do not know what theye might be if it is a schmitt input.
  9. Radium

    Radium Guest

    Thermal damage?
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