For JFET and MOSFET, consider the following statements : (A) MOSFET is a voltage controlled capacitor...

86) For JFET and MOSFET, consider the following statements :

(A) MOSFET is a voltage controlled capacitor

(B) BJT is slower than FET

(D) Leakage currents are zero in FET

(E) MOSFET are slower than JFET

Choose the correct answer from the options given below :

(1) (A), (B) and (C) only

(2) (A), (B) and (D) only

(3) (B), (C) and (D) only

(4) (B) and (E) only

Answer: A

Solution

(A) MOSFET is a voltage controlled capacitor: True. The capacitance of the MOS structure depends on the applied gate voltage, which controls the depletion/inversion regions.
(B) BJT is slower than FET: True. BJTs are bipolar (minority carrier) devices and suffer from carrier storage effects, making their switching speed slower than unipolar (majority carrier) FETs.
(C) Input impedance of MOSFET is greater than JFET: True. A MOSFET has an insulated gate (using
```
 $S i O_{2}$ 
```
), leading to extremely high input impedance (
```
 $10^{10}$ 
```
to
```
 $10^{15} Ω$ 
```
), whereas a JFET uses a reverse-biased PN junction (
```
 $10^{9} Ω$ 
```
).
(D) Leakage currents are zero in FET: False. While they are very small (picoamps to nanoamps), they are not zero.
(E) MOSFET are slower than JFET: False. Modern MOSFETs are designed for very high-speed switching and generally outperform standard JFETs in this regard.

Statements (A), (B), and (C) are correct.
Answer: (1)