4. Operating classes

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...