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virtual ground

Discussion in 'Electronic Basics' started by novice, Dec 25, 2005.

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  1. novice

    novice Guest

    what is a virtual ground in op-amps? how is it different from normal
    ground?is virtual ground concept used in any other amplifiers? thanks
    a lot in advance
  2. Virtual ground is a copy of ground potential created by an amplifier
    that is not actually connected directly to ground. It is the input
    node of a current summing negative feedback amplifier. The amplifier
    produces whatever output voltage is necessary to soak up all the
    current arriving at the input node from some signal voltage or current
    source, through some input network, through some other network between
    the output and the input node. To the input signal, it appears that
    the input network is connected to ground, but it is just anode forced
    to stay very close to ground potential by the negative feedback
    network and the high gain of the amplifier.

    One of the uses for it is to sum two signals, with no bleed over of
    one signal into the other. If each is connected to the virtual ground
    node through, say, a resistor, each signal voltage is converted to a
    proportional current, but each input acts as if that resistor were
    just tied to ground, so there is no cross talk between the two
    signals, just loading to ground. In the mean time, the amplifier
    adjusts the output voltage so that the feedback network passes all the
    current provided by both input signals, in a way that balances the
    input voltage very close to zero volts. The inputs and outputs just
    sort of pivot on the input node like a voltage see saw.
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