Field Effect Transistors (FETs): JFET and MOSFET Basics Quiz Quiz

Explore the essential principles of Field Effect Transistors with this quiz designed to test your understanding of JFET and MOSFET basics. Assess your knowledge of FET structure, operation, characteristics, and differences between MOSFET and JFET devices in analog and digital circuits.

1. FET Input Impedance

   Which property of a Field Effect Transistor (FET) makes it especially suitable for use as an input stage in amplifiers where minimal current is desired from the signal source?

   1. High input impedance
   2. Fast switching time
   3. Low source voltage
   4. Large gate current

   Explanation: FETs have high input impedance, which means they draw very little current from the signal source, making them ideal for sensitive amplifier stages. Low source voltage is not a defining property of FETs. Large gate current is actually undesirable since FETs ideally have negligible gate current. Fast switching time is beneficial but does not directly relate to minimizing current drawn from the input.

2. JFET Channel Control

   In an N-channel JFET, how does applying a more negative gate-to-source voltage (Vgs) affect the drain current (Id), assuming drain-to-source voltage is held constant?

   1. Drain current increases
   2. Drain current stays the same
   3. Drain current decreases
   4. Channel becomes wider

   Explanation: Increasing the negative gate-to-source voltage in an N-channel JFET causes the depletion region to widen, narrowing the channel and reducing the drain current. If the drain current increased, it would contradict the pinch-off characteristic. Drain current only stays the same if Vgs does not change, and the channel actually becomes narrower, not wider.

3. MOSFET Structure

   Which terminal of a MOSFET is electrically insulated from the main channel by a thin oxide layer, helping to achieve extremely low gate current during operation?

   1. Drain
   2. Bulk
   3. Gate
   4. Source

   Explanation: The gate of a MOSFET is separated from the channel by a thin insulating oxide layer, resulting in very low gate current. The source and drain are connected to the channel and do not provide insulation. The bulk (or substrate) is not the main insulated terminal in this context. This insulation distinguishes MOSFETs from other FETs such as JFETs.

4. Enhancement vs. Depletion Mode

   When using an N-channel enhancement-mode MOSFET, what must be applied to the gate for the device to conduct significant current between drain and source?

   1. Alternating voltage
   2. A positive voltage relative to source
   3. A negative voltage relative to source
   4. Zero voltage

   Explanation: An N-channel enhancement-mode MOSFET requires a positive gate-to-source voltage to create a conducting channel, allowing drain current to flow. Applying a negative voltage suppresses conduction. Zero voltage means there is no enhancement and the channel remains off for an enhancement-mode device. Alternating voltage can switch the device, but to turn it 'on,' a positive DC voltage is specifically required.

5. FET Symbol Identification

   In standard circuit symbols, which feature distinguishes the symbol of a MOSFET from that of a JFET when shown on a schematic diagram?

   1. Dotted circle around the symbol
   2. Arrow direction on the source terminal
   3. Double lines at the gate terminal
   4. Insulating gap between gate and channel

   Explanation: The MOSFET symbol includes an insulating gap between the gate and channel to represent the oxide layer, visually distinguishing it from the continuous connection in a JFET symbol. The arrow direction on the source shows channel type but does not distinguish between JFETs and MOSFETs. Double lines at the gate are not standard for FET symbols. There is no dotted circle conventionally used in these transistor symbols.