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What makes an amplifier a class AB amplifier?
If the class AB operating point is closer to the class A operating point (resp. class B) than the class B operating point (resp. class A) the circuit will behave more such as a class A amplifier (resp. class B) by presenting a higher linearity but a lower efficiency (resp. higher efficiency but lower linearity).
Where is the biasing point of a Class B amplifier?
Class B Amplifier Operation For Class B amplifier operation, two complimentary switching transistors are used with the Q-point (that is its biasing point) of each transistor located at its cut-off point. This allows for one transistor to amplify the signal over one half of the input waveform, while the other transistor amplifies the other half.
Why are class AB amplifiers cannot be used in push pull configuration?
The main reason why this configuration cannot be used for class AB amplifiers is that the set of values of the resistors will only work for a particular push-pull configuration. Moreover, the set of values needs to be chosen very carefully, specially if the complementary transistors are different.
What is the efficiency of a Class A amplifier?
If the class AB amplifier is biased at the limit of the class A operating point, V AC,max =V supply /2 and thus ηmax=π/8=39.3 %. In the other cases, the maximum efficiency of a class AB amplifier will be in the ]39.3 % ; 78.5 % [ range.
When does distortion occur in an AB amplifier?
The transistors do not go into its full off range. This is achieved by implementing two diodes in the circuit. With AB amplifiers, distortion is worst when the signal is at its minimum value. Paradoxically, the distortion is at its lowest when the signal reaches it clipping point.
Why do class AB amplifiers have PNP transistors?
We can note that a small portion of the signal is conducted simultaneously by the NPN and the PNP transistors. This ensures that no crossover distortion is observed during the amplification performed by class AB amplifiers.