GATE EC 2019 Set 1 — Question 19
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Electronic Devices → BJT → Structure & Operation
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Question
The correct circuit representation of the structure shown in the figure is
Correct answer
(A) [figure]
Solution
The given structure shows a Bipolar Junction Transistor (BJT).
Let's identify the regions and their doping types:
Let's identify the regions and their doping types:
- The top layer is labeled 'B' and is . This is the Base.
- The region below 'B' is 'n'. This is the Collector.
- The region on the right, labeled 'C', is . This is the Emitter.
- The region on the left, labeled 'E', is . This is also the Emitter.
1.Emitter (E): The heavily doped region on the right, labeled 'E'. This is typically the most heavily doped region.
2.Base (B): The region, labeled 'B', which is between the emitter and collector.
3.Collector (C): The 'n' region, labeled 'C', which surrounds the base and emitter. This is typically lightly doped.
The structure is (Emitter) - (Base) - (Collector). This indicates an NPN transistor.Now let's look at the circuit symbols for an NPN transistor:- The arrow on the emitter points outwards from the base.
- The base is connected to the region.
- The collector is connected to the region.
- Option (A): Shows an NPN transistor. The base is connected to 'B', the collector to 'C', and the emitter to 'E'. This matches the NPN structure identified.
- Option (B): Shows a PNP transistor (arrow points inwards). This is incorrect.
- Option (C): Shows an NPN transistor, but the connections are swapped for collector and emitter compared to the labels in the diagram. The 'C' terminal is connected to the emitter and 'E' to the collector. This is incorrect based on the physical layout and typical BJT labeling.
- Option (D): Shows a PNP transistor. This is incorrect.
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