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4. Operating classes
The qualities required of an amplifier are numerous and often contradictory: efficiency, linearity, gain, output power, noise figure... Depending on the application, neither the same components nor the same amplifier structure are chosen.
4.1 Class A
Class A is generally chosen for better linearity. In class A, the transistor is constantly conducting, there is no threshold effect on the output signal, and distortions of the output signal arise solely from the non-perfect linearity of the transfer characteristic (a defect that is particularly noticeable for large excursions around the quiescent point).
Low-level amplifiers (low-noise amplifiers, for example) are Class A but with a quiescent point chosen to minimize noise (typically I...
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Operating classes
Microwave-specific structures
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