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virtual ground

N

novice

Jan 1, 1970
0
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
 
J

John Popelish

Jan 1, 1970
0
novice said:
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
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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