Question

in saturation region of a bjt: transistor behaves like a closed switch both junctions are forward biased collector current ≈ β x base current both junctions are reverse biased transistor behaves like an amplifier in a common emitter amplifier, what is the role of the coupling capacitor? to amplify the signal to block dc and pass ac signals between stages to stabilize the emitter current to provide biasing for the transistor

Explanation:

1. In the saturation region of a BJT, the transistor behaves like a closed - switch and both junctions are forward - biased. The relation Collector current ≈ β×base current holds in the active region, not saturation. Both junctions are reverse - biased in the cutoff region and the transistor acts as an amplifier in the active region.
2. In a Common Emitter amplifier, the coupling capacitor blocks DC and passes AC signals between stages. It doesn't amplify the signal (amplification is done by the transistor), doesn't stabilize the emitter current (emitter resistors or other biasing techniques do that), and doesn't provide biasing for the transistor (biasing circuits do that).

Answer:

1. Transistor behaves like a closed switch, Both junctions are forward biased
2. To block DC and pass AC signals between stages