How does the construction of a MOSFET help to achieve high input impedance?
The gate is insulated from the channel by a thin oxide layer
The question asks about the construction of a Metal-Oxide-Semiconductor Field-Effect Transistor (MOSFET) and how it achieves high input impedance. Let's explore the concept:
MOSFET Structure and High Input Impedance:
- A MOSFET consists of three terminals: Gate, Drain, and Source. Additionally, it has a substrate made of semiconductor material.
- The key feature of a MOSFET that results in high input impedance is the thin oxide layer between the gate and the channel (the path between the source and the drain).
- This oxide layer is typically Silicon Dioxide (SiO2), which is an excellent insulator.
Explanation:
- The gate electrode is insulated from the channel by this thin oxide layer.
- Because of this insulation, there is virtually no direct path for current to flow into the gate, significantly increasing the input resistance or impedance of the MOSFET.
- This means that no significant current flows into the gate; instead, it controls the channel conductivity by capacitive action.
- High input impedance is advantageous because it reduces the load on the preceding stage in an electronic circuit.
Evaluating Options:
- The gate is insulated from the channel by a thin oxide layer (Correct option): As discussed, this insulation leads to high input impedance due to the absence of a direct DC path for current between the gate and the channel.
- The gate uses a resistive layer to limit current: This is incorrect because a resistive layer would not provide the high impedance structure characteristic of a MOSFET.
- The gate is connected directly to the channel: This would lower input impedance, contrary to MOSFET design.
- The device has a thick substrate for support: While substrate support is necessary, it does not contribute to the high input impedance of a MOSFET.
Therefore, the correct answer is that the gate is insulated from the channel by a thin oxide layer, providing the MOSFET with high input impedance.
Similar Questions
Which set of terminals is commonly used to connect a Field Effect Transistor in a circuit?
In an n-channel enhancement mode MOSFET, what must be applied to the gate terminal relative to the source to turn the device on?
What is the configuration called when the emitter terminal of a transistor is common to both input and output circuits?
While diagnosing an NPN BJT in a SOT-23 package, your multimeter positive probe (+) is locked on the Base (Pin 1). Measuring to Pin 3 reads 0.6 V, while measuring to Pin 2 reads 0.68 V. Which pin is the Emitter?
Which type of charge carriers mainly control current in a Field Effect Transistor (FET)?
Why are transistors preferred over mechanical switches for rapid switching operations?
What is the purpose of the base region in an NPN transistor?
In the output characteristics of a common-emitter configuration, a family of curves is obtained by varying VCE while keeping which quantity fixed? (Symbols have their usual meaning.)
The common-emitter (CE) configuration of a transistor is most widely used as a/an:
Important Questions from Transistors
Heat sink of a power transistor can be used for:
Transistors used as power amplifiers are generally mounted on a metallic plate so as to-
MOSFET can be used as a
In a C-E configuration, an emitter resistor is used for:
Which of the following transistor amplifier configuration is used as a buffer for impedance matching.
