Question

In integrated circuits, NPN construction is preferred to PNP construction because:
A) NPN construction is cheaper
B) To reduce diffusion constant, n-type collector is preferred
C) NPN construction permits higher packing of elements
D) P-type base is preferred

Answer 1

Hint-The integrated circuits are made up of hundreds of transistors, resistors, capacitors etc. The integrated circuits are used as amplifiers, oscillators, microprocessors, memory elements etc. The transistors are made up of semiconductors. It is the fusing of oppositely doped semiconductors in between the similarly doped semiconductors. There are two types of transistors. They are NPN and PNP according to the fusion of doping materials.

Complete step by step answer:
(i) In PNP transistors, the negatively doped semiconductor is placed in between the two positively doped semiconductors. Hence there are more holes in the transistor. It provides positive power to the output. Thus, it is called as “sourcing sensors”

(ii) In NPN transistors, the positively doped semiconductor is placed in between two negatively doped semiconductors, hence there are more electrons in this transistor. It sinks the ground to the output. Thus, it is called as “sinking sensors”

(iii) In both transistors the charge carriers are holes and electrons. The charge carriers’ electrons and holes diffuse into the material. This movement of charge carriers causes diffusion. The diffusion causes the current to flow in the semiconductor material.

(iv)The diffusion constant is low in the NPN transistors. Hence it is used in the integrated circuits.

Thus, the correct option is B.

Note:
The transistors are used as oscillators and amplifiers. In the transistor, unless the current flows in the base circuit, there is no current that can flow in the collector circuit. This property allows the transistors to work as a switch.
Note In integrated circuits, NPN construction is preferred to PNP construction because:
A) NPN construction is cheaper.
B) n-type is preferred for reducing the diffusion constant.
C) NPN construction permits higher packing of elements.