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A perfect amplifier with
an amplification of
times 10, as shown
above, would give an
output 10 times greater
than the input, NO
MATTER WHAT THE INPUT
FREQUENCY.
If the input was 10 mV
then the output would be
100 mV, no matter the
frequency of the input
signal, as seen in the
graph below.
This graph is known as a
FREQUENCY RESPONSE
diagram.
In a practical amplifier
it is not possible to
obtain a perfectly flat
response curve.
This is due to
limitations of
electronic components
and circuitry.
Usually there is a fall
of response at low and
high frequencies.
The two points in red on
the response curve mark
where the output of the
amplifier has fallen to
70.7 % of the maximum
output.
This means that that the
100mV output has fallen
to 70.7 mV at these
frequencies.
These are called the -3
dB points.
One is at about 5Hz
(call it f1).
The other is at about
900 kHz (f2).
Subtract f1 from f2 to
get the BANDWIDTH of the
amplifier.
In this case it is just
under 900 kHz wide.
In some cases the
bandwidth is tailored to
pass some frequencies
and not others.
This is called
FILTERING.
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