RF Electronics Chapter 10: Operational Amplifiers Page 341
2022, C. J. Kikkert, James Cook University, ISBN 978-0-6486803-9-0.
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∗ Eqn. 10.4
When A(s) = G the gain will be 3 dB below the gain when A(s) is very large. The
frequency when A(s) = G is thus the bandwidth of the amplifier. Since A(s) decreases
with frequency as shown in figure 2, the bandwidth of the amplifier will depend on the
gain as is also shown in figure 2.
Figure 10.2. Open loop and Closed loop gain of Voltage Feedback Amplifier [1]
If D is the distortion introduced by the amplifier, the distorted gain Ad(s) is then;
Ad
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s
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� A
�
s
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∗
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Eqn. 10.5
Then the gain of the amplifier can then be written as:
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�� Eqn. 10.6
The larger A(s), the smaller the effect of the distortion D. OpAmps are thus very useful
in producing low distortion amplifiers.
Current Feedback Amplifier Theory
The Current feedback amplifier produces an output voltage proportional to an "Error
current" I
error
. The Current feedback amplifier "gain" is the transfer impedance Z(s).
Figure 10.3 Current Feedback amplifier configuration [1]
For the inverting amplifier configuration of figure 10.1, the equations for the amplifier
are:
RF Electronics: Design and Simulation
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