As the name indicates, class AB amplifiers operate somewhere between class A and class B. Or perhaps the name is short for "Almost B" -- which would be true as well.

A class A amplifier operates at a full 360 degrees. The purity of amplification is terrific, but the efficiency is not.

Class B amplification uses two "finals", each operating for 180 degrees of the wave -- a great improvement in efficiency. However, with the introduction of bipolar transistors as finals, a problem with class B amplification developed. In a pure class-B configuration, there is a period of time where neither the forward-going nor the negative-going final has a forward-biased base-emitter junction. When this type of amplifier is fed a pure sine wave, there is a "hitch" at the zero crossing caused by neither final being forward-biased. This is called crossover distortion, and is a highly undesirable alteration of a pure sine wave.

The simple and elegant solution to this was to bias the finals so that each one operates slightly more than 180 degrees (but less than 360 degrees) to eliminate the problem of crossover distortion. The result is an amplifier with "Almost Class B" efficiency, but with distortion characteristics close to class A. Or, as it is called, Class AB.

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Just remember that the key feature of Class D amplifiers is high efficiency.

Each one of the wrong answers misleads you by putting the letter D in the description: differential, drift-mode, and doubling.

Trick: Class D, D is for Digital -> Technology is the answer.

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Setting the bias half-way between saturation and cutoff gives the maximum possible swing in collector voltage without entering either saturation or cut- off.

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Unwanted oscillations are also called parasitic oscillations. Naturally, a parasitic suppressor suppresses parasitic oscillations.

SWR, power, and phase are all more or less unrelated to oscillation.

Silly Hint: Parasites are unwanted

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Memory Aid: The ground is under your feet so it is low and won't impede your walk.

Compare to transistor base, collector, emitter. Which common lead type has low impedance? Which lead is like the grid in a vacuum tube?

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From Wikipedia: "Class-C amplifiers conduct less than 50% of the input signal and the distortion at the output is high". So, the option that mentions distortion is correct.

Silly hint: Class C - correct answer contains words starting with the next letters in the alphabet; signal distortion and excessive bandwidth. (c, d, &e).

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Linear amplifiers (such as Class A amps) bias transistors in their linear region. Whenever these transistors are conducting they are never fully on nor off, but have some instantaneous resistance which generates heat.

An ideal switch when closed has 0 ohms of resistance, and when open has infinite resistance. In either case the switch does not generate any heat.

Transistors in switching amplifiers act much like switches--they are either on or off most of the time. Because switched transistors are seldom partially on they don't generate much heat, resulting in low power dissipation compared to transistors operating in their linear region.

Hint: 'linear' descriptor of time, only answer with 'time'

Hint: The only one that doesn’t say amplifier

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