Which of the following terminals does not belong to the MOSFET?

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Examoogle · Accepted Answer

Base

Explanation: A MOSFET (Metal-Oxide-Semiconductor Field-Effect Transistor) is a voltage-controlled device consisting of three main terminals: Gate, Drain, and Source. The 'Base' terminal is characteristic of Bipolar Junction Transistors (BJTs), not MOSFETs.

Working Principle: The MOSFET operates by creating an electric field between the Gate and the channel region. This field modulates the conductivity of the channel, allowing current to flow between the Source and the Drain. The Base terminal in a BJT, by contrast, controls current via charge carrier injection, which is fundamentally different from the capacitive field-effect mechanism of a MOSFET.

Key Formulas: $I_D = \mu_n C_{ox} \frac{W}{L} [(V_{GS} - V_{th})V_{DS} - \frac{V_{DS}^2}{2}]$ — Drain current in the linear region; $I_D = \frac{1}{2} \mu_n C_{ox} \frac{W}{L} (V_{GS} - V_{th})^2$ — Drain current in the saturation region

Key Points: MOSFET terminals: Gate, Drain, Source.; BJT terminals: Base, Collector, Emitter.; MOSFETs are unipolar devices (current carriers are of one type).; BJTs are bipolar devices (current involves both electrons and holes).

Advantages: High input impedance; High switching speed; Low power consumption

Disadvantages: Susceptible to electrostatic discharge (ESD); Lower current handling compared to some BJTs

Applications: Digital logic circuits; Power converters and switching supplies; Microprocessors

Additional Info: In MOSFETs, the Gate is electrically isolated from the channel by a thin insulating layer (usually $SiO_2$).. Option C is the correct answer because the term 'Base' refers to the input control terminal of a Bipolar Junction Transistor (BJT), not a MOSFET.

Answer: C is correct — The Base terminal belongs to a BJT, whereas a MOSFET utilizes Gate, Drain, and Source terminals.

Exam Tip: Always remember the mnemonic: MOSFET uses Gate/Drain/Source, while BJT uses Base/Collector/Emitter. This distinction is foundational for all transistor-based circuit analysis.

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