NTA UGC NET/JRF Exam, June -2021 (Electronic Science)

91. Read the passage given below and answer the question:

The Metal Oxide Semiconductor Field Effect Transistor (MOSFET) is the most important device at the forefront of high-density integrated circuits such as microprocessors and semiconductor memories. It is also becoming an important power device. The principle of the surface field-effect transistor was first proposed in the 1930s and the first MOSFET was reported in 1960 using the Si-SiO2 system.

The current in MOSFET is transported by carriers of one polarity only and hence it is usually referred to as a unipolar device. Although MOSFETs have been made with various semiconductors, such as Ge, Si, and GaAs and use various insulators such as SiO₂, Si₃N₄ and Al₂0₃, the most important system is Si-SiO₂.
The drain current density including both drift and diffusion component is given by:

Correct Answer: D.

92. The drain current density including both drift and diffusion component is given by:

Correct Answer: C.

93. The channel resistance of an elemental section dy is:

Correct Answer: B.

94. In n-channel MOSFET, the charge induced in the inversion layer per unit area at a distance y from the source is:

Correct Answer: B.

95. The one dimensional Poisson equation for the surface space charge region at the drain is:

Correct Answer: A.

96. Read the passage given below and answer the question:

One very common use of filters is bandwidth limiting. Analog filter implementation consists of two categories: passive and active. The active filters are further classified as high-pass, low-pass, bandpass, band-reject and all-pass. Butterworth and Chebyshev are commonly used practical filters.

The key characteristic of Butterworth filter is that it has a flat passband and stopband. The practical limit for most RC active filters is close to 30 kHz. The Chebyshev response is referred to as an equiripple response because passband is characterised by a series of ripples that have equal maximum levels and equal minimum levels besides exhibiting flat stopband.
Which of the following statements is not correct for a Chebyshev filter?

A. Chebyshev filter tends to exhibit ringing effect with transient signals.
B. Time delay and phase characteristics of Chebyshev filter are comparitively better than that of Butterworth filter.
C. Chebyshev filters have a sharper slope than Butterworth filters.
D. Chebyshev filters are capable of achieving more attenuation in stopband.

Correct Answer: B. Time delay and phase characteristics of Chebyshev filter are comparitively better than that of Butterworth filter.

97. Which of the following statements is not correct about Butterworth filter?

Correct Answer: C.

98. Read the statement.

A. 30 2, 32.5 milli Farads
В. 68 2, 30.5 milli Farads
C. 82 Ω, 3.25 milli Farads
D. 89 2, 2.65 milli Farads

Correct Answer: D. 89 2, 2.65 milli Farads

99. The characteristic equation for the output voltage of an All-pass filter is given by:

Correct Answer: C.

100. Which of the following statements are correct for active filters?

(a) Multiple feedback are preferred for Q≤ 10.
(b) For Q > 10, state variable filter is used.
(c) The upper and lower cut-off frequencies have arithmetic symmetry about centre frequency fa for smaller Q values.
(d) As Q is increased, the filter becomes less selective and both upper and lower cut-off frequencies approximate geometric symmetry.
Choose the correct answer from the options given below: