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The only negative charged electrons are available as negative charges and they accumulate at the surface. Accumulation: An applied positive gate voltage larger than the flat band voltage (V GB > V FB) then a positive charge is induced on the metal (poly silicon) gate and negative charge in the semiconductor.It is defined as the voltage at which there is no charge on the capacitor plates and hence there is no static electric field across the oxide. The flat band voltage is an important term related to the MOS capacitor.The value of MOS capacitor depends on the region of operation.

A capacitor is formed when two conducting layers are separated by a dielectric layer.An MOS capacitor is made of a semiconductor body or substrate, an insulator film, such as SiO2, and a metal electrode called a gate.

Another region inverse active region is of less importance in practice. Common Base (CB) amplifier, Common Emitter (CE) amplifier and Common Emitter (CE) amplifier. There are three types of operating modes of amplifier i.e.

Transistor as an amplifier: Transistor, when used as an amplifier, is operated in the active region in which input junction will be forward biased and output junction will be reverse biased.

The transistor as a Switch: The transistor can be used as a switch in logic gates will be operated in extreme regions of input output characteristics in which both regions will be forward biased (On state) or reverse biased (Off state) which are called saturation and cut off regions of operation simultaneously.

Due to the presence of two junctions each junction can be operated in forward or reverse bias leading to three different regions of operation.

They are Common Base, Common Emitter, and Common collector configurations.

BJT can be operated in three configurations.In typical operation, the emitter–base junction is forward biased and the base–collector junction is reverse biased. An NPN transistor can be considered as two diodes with a shared anode region.The direction of arrow signifies the direction of emitter current when base emitter junction is forward biased.