Small Signal Amplifiers Questions and Answers

Answer: A

Power gain is the product of voltage and current gain, which is why common emitter beats the other two configurations on that measure: common base has no current gain and common collector no voltage gain. The other combinations describe the intrinsic gain, an impedance ratio and the gain-bandwidth product. Which figure of merit to quote depends on what the stage is for, and power gain is the one that ranks the three configurations most clearly.

Answer: B

Common emitter offers both voltage and current gain, so their product is the largest of the three - typically tens of thousands. Common base gives voltage gain with a current gain just under one, and common collector the reverse, so each is limited to roughly the one gain it has. That the default choice for a general amplifier stage is also the one with the highest power gain is no accident, and it is the reason it became the default.

Answer: C

The first two are correct and the third is the reverse: a current source needs some voltage across it to remain a current source, so headroom is lost rather than gained. The gain and area benefits are real and are why the technique dominates integrated design. A statement that reverses the cost of a technique into a benefit is worth checking against what the component physically requires.

Answer: D

The first is true and the second is false: the gain rises because the load impedance is high, and the swing falls because the current source needs headroom of its own. The two move in opposite directions, which is exactly the trade the technique makes. Being able to name both directions of a change is what distinguishes understanding a technique from having heard of it.

Answer: A

A higher gain per device is not among them - each half of a pair gives about the same gain as a single stage, and the differential gain is comparable rather than larger. The other three are the real advantages, all following from the symmetry. A topology adopted for its rejection and stability rather than for raw gain is worth recognising as such, since expecting extra gain from it leads to disappointment.