some word confusion

Discussion in 'General Electronics Chat' started by shaking928, Nov 26, 2004.

  1. shaking928

    Thread Starter New Member

    Nov 8, 2004
    4
    0
    why do your enlish men define power supplies of Op amp as a rail or rail-to-rail voltage?how to explain the word "rail"?
    "subharmonics" is just another word confusing me a lot.why is it made?
     
  2. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
    282
    Hi,

    Technical English can be hard to understand.

    The "rails" thet are speaking about are the power supply voltages. This term comes from the past, when it was customary to draw the positive voltage line and the negative voltage line as the upper and lower lines on schematics with the circuit symbols in between. As such, the voltage supply lines were parallel and spaced apart like train track rails.

    An amplifier cannot swing its output as far as the voltage supply potentials. "Rail to rail" amps have charge pumps incorporated to boost the internal voltage such that the output waveform can equal the power supply potentials.

    Subharmonics are those harmonics whose frequencies lie below that of the fundamental. For 100 Hz, the first even subharmonic is 50 Hz.
     
  3. pebe

    AAC Fanatic!

    Oct 11, 2004
    628
    3

    <!--QuoteBegin-beenthere
    @Nov 27 2004, 08:32 PM
    .......An amplifier cannot swing its output as far as the voltage supply potentials. "Rail to rail" amps have charge pumps incorporated to boost the internal voltage such that the output waveform can equal the power supply potentials.....[/quote]As far as I am aware, op-amps with FET output stages can swing rail to rail.
     
  4. bodhisatva

    Member

    May 20, 2004
    23
    0
    There are not only charge pumps inside but other techniques to achieve "rail-to-rail" output, most of them are with CMOS opamps. Ofcourse usualy you still have at about 20mV more or less the power rails.
     
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