Discussion
Consider the following circuit configurations :
1. Common emitter
2. Common base
3. Emitter follower
4. Emitter follower using Dartington pair The correct sequence in increasing order of the input resistances of these configurations is
Answer: C
The input resistance rises in the order common base (2), common emitter (1), emitter follower (3), and emitter follower using a Darlington pair (4): the common base stage has a very low input resistance, the common emitter stage a moderate one of about \( h_{ie} \), the emitter follower a high one of about \( \beta R_E \), and the Darlington pair increases it further because its current gain is the product of two stages. That order is 2, 1, 3, 4, option C. Options A and B place the Darlington pair below the simple follower, and option D puts the common emitter stage below the common base stage.
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