Question

Which of the following is a characteristic that distinguishes a JFET from a MOSFET?

• A. JFETs are voltage-controlled, while MOSFETs are current-controlled devices
• B. MOSFETs can only operate in depletion mode, whereas JFETs can operate in both depletion and enhancement modes
• C. JFETs have a higher input impedance compared to MOSFETs
• D. MOSFETs are controlled by voltage applied to their gate, whereas JFETs are controlled by the current

Hint:

Remember: MOSFET = voltage gate, JFET = junction gate. One uses insulation, the other uses a junction.

Answer 1

The Correct Option is D

The fundamental difference between a JFET (Junction Field Effect Transistor) and a MOSFET (Metal-Oxide-Semiconductor FET) lies in how they are controlled:
- MOSFETs are voltage-controlled devices. A voltage applied to the insulated gate controls the current through the channel, with virtually no gate current due to the oxide insulation layer. - JFETs are current-controlled in the sense that the gate-source voltage controls the current flow, but there is some gate current due to the PN junction.
MOSFETs offer extremely high input impedance due to the insulating oxide layer, which distinguishes them from JFETs in practical circuit design.
Why the other options are incorrect:

• (A) Incorrect — it reverses the actual control mechanisms.
• (B) JFETs operate only in depletion mode; enhancement mode is a feature of certain MOSFETs.
• (C) MOSFETs generally have higher input impedance than JFETs.

Hence, the correct distinguishing feature is that MOSFETs are voltage-controlled via the gate, while JFETs are influenced by current through their junction.