FET Concepts: Statement Analysis

We need to evaluate the correctness of the three statements regarding Field-Effect Transistors (FETs).

Statement 1: MOSFET Input Impedance vs JFET

This statement claims MOSFETs have very low input impedance compared to JFETs.

• MOSFETs: Utilize an insulated gate, resulting in extremely high input impedance (typically $10^{10}$ to $10^{15} \Omega$).
• JFETs: Have a reverse-biased gate-source PN junction, providing high input impedance (typically $10^8$ to $10^{10} \Omega$), but significantly lower than MOSFETs.

Therefore, MOSFETs provide very high, not low, input impedance compared to JFETs. Statement 1 is incorrect.

Statement 2: Depletion-Type MOSFET Operation

This statement discusses the operating modes of a depletion-type MOSFET.

• A depletion-type MOSFET has a channel that exists even with zero gate-source voltage ($V_{GS}=0$).
• Depletion Mode: Achieved when $V_{GS}$ is negative, reducing the number of charge carriers in the channel and decreasing drain current ($I_D$).
• Enhancement Mode: Achieved when $V_{GS}$ is positive, attracting more charge carriers to the channel and increasing $I_D$.

Thus, a depletion-type MOSFET can operate in both modes. Statement 2 is correct.

Statement 3: FET Biasing for Amplification

This statement addresses the required biasing region for FETs in amplifier applications.

• For amplification, the FET must operate in a region where the drain current ($I_D$) is primarily controlled by the gate-source voltage ($V_{GS}$) and is relatively independent of the drain-source voltage ($V_{DS}$).
• This characteristic is found in the saturation region of the FET's operation.

Therefore, biasing the FET in the saturation region is essential for its use as an amplifier. Statement 3 is correct.

Conclusion on Correct Statements

Based on the analysis, statements 2 and 3 are correct, while statement 1 is incorrect.

The correct option is the one that includes only statements 2 and 3.