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The opamp has a very
high gain, typically
(100 dB)100,000 times.
Looking at the left hand
diagram, an input with a
swing of a fraction of a
millivolt produces an
output that changes
between + 12 volts and -
12 volts.
In most cases this gain
is excessive, and is
reduced by negative feed
back.
Looking at the right
hand diagram we can see
that the opamp amplifies
right down to dc.
Gain falls quite rapidly
as the frequency
increases.
In fact the bandwidth
(the point at which the
output has fallen by 3
dB) is only 1 kHz.
This is also improved
upon by the use of
negative feedback.
The input impedance is
high, 1M.
The output impedance is
low, 150 ohms.
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