GATE 1990 ECE Analog Circuits (Analog Electronics) - Video Solutions

1. For good stabilized biasing of the transistor of the CE amplifier of the figure shown, the condition is

Answer: B

Solution : https://www.youtube.com/watch?v=fm8C06N2YjU


2. Which of the following statements are correct for biasing transistor amplifier configurations?
a. CB amplifier has low input impedance and a low current gain
b. CC amplifier has low output impedance and a low current gain
c. CE amplifier has very poor voltage gain but has very high input impedance
d. The current gain of CB amplifier is higher than the current gain of CC amplifier

Answer: A

Solution : https://www.youtube.com/watch?v=5PMMEFOSckU


3. For the same a.c. voltage and load impedance, which of the following statements about rectifier are correct?
a. The average load current in a full wave rectifier is twice than in a half wave rectifier
b. The average load current in a full wave rectifier is n times that in a half wave rectifier
c. Half wave rectifier will have a bigger sized transformer compared to full wave rectifier
d. Half wave rectifier will have a small sized transformer compared to full wave rectifier

Answer: A & D

Solution : https://www.youtube.com/watch?v=B6rB6cVX0L4


4. The operational amplifier has a very poor open loop gain of 45, otherwise is ideal. The gain of the amplifier is

a. 5
b. 20
c. 4
d. 4.5

Answer: D

Solution : https://www.youtube.com/watch?v=AKfkDdQUCk4


5. The CMRR of the differential amplifier shown is

a. Infinity
b. Zero
c. 900
d. 1800

Answer: C

Solution : https://www.youtube.com/watch?v=p4ZPC8J4Nb8


6. If the input to the circuit shown is a sine wave, the output will be

a. Half wave rectified sine wave
b. Full wave rectified sine wave
c. Triangular wave
d. Square wave

Answer: D

Solution : https://www.youtube.com/watch?v=C0HGrOgrvrE


7. Figure shows an RC phase shift oscillator.

Solve the network to find the minimum value of h_fe for the transistor for oscillations to be possible. Also determine the frequency of such oscillations. Take C = 0.01 µF and h_ie = 2 KΩ.

Answer: 56 and 5 KHz

Solution: https://www.youtube.com/watch?v=xupn6VebQzg


8. A pick up signal is power amplified using a complementary symmetry push pull amplifier and fed to a 5 Ω loud speaker as shown.

The specifications of power transistors are as follows:
I_Cmax = Maximum collector current = 2 Amps and P_Cmax = Maximum power dissipation = 1 Watt.
Find the maximum power delivered to the loud speaker, if the maximum output voltage subject to OP-AMP voltage limitations is 15 volts.
If the transistors are mounted on a heat sink, so that P_Dmax changes to 3 Watts. What will be the new value of the maximum power delivered?

Answer: (i) 3.08 Watts, circuit gets breakdown (ii) 3.08 Watts, circuit gets breakdown

Solution: https://www.youtube.com/watch?v=Y0bFRK_uSuY

GATE 1990 Video Solutions on Digital Circuits

1. The number of Boolean functions that can be generated by n variables is equal to :

Answer:B

Solution : https://www.youtube.com/watch?v=cbcw8w6W5-M


2. The minimal function that can detect a “divisible by 3” 8421 BCD code digit (representation is D₈D₄D₂D₁) is given by

Answer:B

Solution : https://www.youtube.com/watch?v=JuFxnaN__Z8


3. A 4 bit modulo-16 ripple counter uses JK flip-flops. If the propagation delay of each flip-flop is 50 nsec, the maximum clock frequency that can be used is equal to ……
a. 20 MHz
b. 10 MHz
c. 5 MHz
d. 4 MHz

Answer: C

Solution : https://www.youtube.com/watch?v=v4RIzGm0DGY


4. Which of the following resistance networks can be used as 3 bit R-2R ladder DAC? Assume V_o corresponds to LSB.

a. Both (i) and (ii)
b. Both (i) and (iii)
c. Only (iii)
d. Only (ii)

Answer:C

Solution : https://www.youtube.com/watch?v=CQEUnS3slF4

GATE 1990 Electronic Devices (EDC) Video solutions

1.  In a uniformly doped abrupt PN junction, the doping level of the N-side is four times the doping level of the P-side. Then the ratio of the depletion layer widths is......

Answer:

W_n / W_p = 1 / 4

Solution :  http://www.youtube.com/watch?v=ddZ7Kuje6E8


2. In a semiconductor, under high electric fields, with increasing electric fields, mobility of charge carriers ............. and velocity of charge carriers ..............

Answer: Reduces, Gets saturated so remains constant.

Solution : http://www.youtube.com/watch?v=8cjTRCdTpbk


3. In a forward biased photo diode, with increase in incident light intensity, the diode current
       a.  increases
       b.  remains constant
       c.  decreases
       d.  remains constant, but the voltage drop across the diode increases.

Answer: A

Solution :  https://www.youtube.com/watch?v=dBkgMBzNyYA

4.  In a junction diode,
       a. the depletion capacitance increases with increase in the reverse bias
       b. the depletion capacitance increases with decrease in the reverse bias
       c. the diffusion capacitance increases with increase in the forward bias
       d. The diffusion capacitance is much higher than the depletion capacitance, when it is   
           forward biased.

Answer: B, C, D

Solution :  https://www.youtube.com/watch?v=2Vmo8zKg4vY

5. SCR can be turned On by
       a. Applying anode voltage at sufficiently fast rate
       b. Applying sufficiently large anode voltage
       c. Increasing the temperature of SCR to a sufficiently large value
       d. Applying sufficiently large gate current

Answer: All are correct, most accurate is D

Solution :   https://www.youtube.com/watch?v=U0x31gFcggQ

6. The pinch off voltage of a JFET is 5.0 volts. Its cutoff voltage is

Answer: 5 volts

Solution :  https://www.youtube.com/watch?v=YZcn5Y_9p14

7.  Which of the following effects can be caused by a rise in the temperature ?
       a. Increase in MOSFET current
       b. Increase in BJT current
       c. Decrease in MOSFET current
       d. Decrease in BJT current

Answer: B,C

Solution : https://www.youtube.com/watch?v=BoRoLQ2eN6o

8. (a) Two ideal and identical junction diodes (with ideality factor Ƞ = 1) connected in series as shown below.

Show that exp(eV1/KT) + exp(-eV2/KT) = 2, where V1 and V2 are the voltage drop across the diodes D1 and D2.

(b) Assuming that the current flowing through the reverse biased diode is saturated at I_CO, calculate the voltage drop across the forward biased diode. Assume KT = 26 meV.

Answer: (b) 0.018 volts

Solution :   https://www.youtube.com/watch?v=qz6ZD9Y5nUo

9. In a semiconductor at room temperature, the intrinsic carrier concentration and resistivity are 1.5 X 10¹⁶ m^-3 and 2 X 10⁵ Ω-m respectively. It is converted into an extrinsic semiconductor with a doping concentration of 10²⁰ per m³. For the extrinsic semiconductor, calculate the

a.       Minority carrier concentration

b.      Resistivity

c.       Shift in Fermi level due to doping

d.      Minority carrier concentration when its temperature is increased to a value at which the intrinsic carrier concentration doubles.

Assume the mobility of majority and minority carriers to be the same and KT = 26 meV at room temperature.

Answer:

a) 2.25 x 10¹² /m³

b) 60 Ω-m

c) 0.228 eV

d) 9 x 10¹² /m³

Solution :    https://www.youtube.com/watch?v=1E491IgBz-I