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Really OLD logic levels

Discussion in 'Electronic Design' started by whit3rd, Apr 4, 2013.

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  1. whit3rd

    whit3rd Guest

    Today we use LVD (low voltage differential) logic, at low voltage levels; before
    that, there was HVD (RS-485), ECL, TTL, DTL, and a few odd items
    like the high-voltage DTL of MC1488, and CML (current-mode
    logic?) and such.

    But 'WAY back there was a system with high power supply voltages
    (about 450V) and very peculiar antenna-based sensing

  2. Guest

    Don't forget the high threshold logic families (15 V) used in
    industrial applications.
    Why would anyone use such high voltages for digital logic ? This
    would require quite high impedance levels and due to the stray
    capacitances, quite slow operation.

    For instance the 5965 double triode was operated at about 100-150 V
    anode voltage supply. The early semiconductor diodes used to build
    diode/tube logic NAND/NOR would not have tolerated much more.

    As strange as it might sound, the early semiconductor diodes were more
    unreliable than tubes.
  3. Tim Williams

    Tim Williams Guest

    I've never heard anything about vacuum state logic levels, if any
    companies even defined their own logic standards -- I would guess
    something in the neighborhood of, say, -20/0V (requires low current C-
    supply) or 50/100V (requires cathode bias = wastes power).

    Tubes aren't so bad. I've done, I think it was -80/0V drive into a sweep
    tube, which is equivalent of driving a 6000V, 1A MOSFET to produce
    sub-150ns edges (comparable to... lazily driving an IRF540, I'd say).
    Such high voltage MOSFETs don't even exist [yet], so I guess toobs win
    that battle. :p
    Umm, read the link..

  4. gregz

    gregz Guest

    I worked with stuff negative voltage, even saw negative logic
    Collins logic, dec logic, zerox logic, general dynamics dynamic logic.

  5. whit3rd

    whit3rd Guest

    It was because the power supplies (highly redundant, a system would operate
    with a few hundred of 'em) weren't regulated, except by corona leakage to atmosphere.

    Higher tech for regulators (gas discharge tubes, Zener diodes, bandgap references)
    was unavailable. :)
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