GATE 2001 ECE Video Solutions on Analog Circuits (Analog Electronics)

1. The current gain of a BJT is
a. g_mr_o
b. g_m / r_o
c. g_mr_π
d. g_m / r_π

Answer: C

Solution: https://www.youtube.com/watch?v=NQcoEO5xLYk


2. The ideal OP-AMP has the following characteristics
a. R_i = ∞, A_V= ∞, R_o = 0
b. R_i = 0, A_V= ∞, R_o = 0
c. R_i = ∞, A_V= ∞, R_o = ∞
d. R_i = 0, A_V= ∞, R_o = ∞

Answer: A

Solution: https://www.youtube.com/watch?v=mtUl2BzGphU


3. Consider the following two statements :
Statement 1: Astable Multivibrator can be used for generating square wave.
Statement 2: Bistable Multivibrator can be used for storing binary information.
a. Only statement 1 is correct.
b. Only statement 2 is correct.
c. Both the statements 1 and 2 are correct.
d. Both the statements 1 and 2 are incorrect.

Answer: C

Solution: https://www.youtube.com/watch?v=HQUPS3pY2A8


4. An NPN BJT has g_m = 38 mA/volt, C_µ = 10^-14 F, C_π = 4x10^-13 F and DC current gain β = 90. For this transistor f_τ and f_β are
a. f_τ = 1.64 x 10⁸ Hz and f_β = 1.47 x 10¹⁰ Hz
b. f_τ = 1.47 x 10¹⁰ Hz and f_β = 1.64 x 10⁸ Hz
c. f_τ = 1.33 x 10¹² Hz and f_β = 1.47 x 10¹⁰ Hz
d. f_τ = 1.47 x 10¹⁰ Hz and f_β = 1.33 x 10¹² Hz

Answer: B

Solution: https://www.youtube.com/watch?v=VJJplixM0a8


5. The following circuit shown in the figure is

a. Hartley oscillator with f_osc = 79.6MHz
b. Colpitts oscillator with f_osc = 50.3MHz
c. Hartley oscillator with f_osc = 159.2MHz
d. Colpitts oscillator with f_osc = 159.2MHz

Answer: B

Solution: https://www.youtube.com/watch?v=U6V6gK9avGY


6. The inverting OP-AMP shown in the figure has an open loop gain of 100. The closed loop gain V_o/V_sis

a. – 8
b. – 9
c. – 10
d. – 11

Answer: B

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


7. In the figure, assume the OP-AMPs to be ideal. The output V_o of the circuit is

Answer: A

Solution: https://www.youtube.com/watch?v=E4dxhaGLiOA


8. An emitter follower amplifier is shown below, where Z_i is the impedance looking into the base of the transistor and Z_o is the impedance looking into the emitter of the transistor.

a. Draw the small signal equivalent circuit of the amplifier.
b. Obtain an expression for Z_i.
c. Obtain an expression for Z_o.
d. Determine Z_i and Z_o, if a capacitor C is connected across R₁.

Answer:
(b) Z_i = r_π + (1 + β)R_L
(c) Z_o = (R_S + r_π)/(1 + β)
(d) Z_i = r_π + (1 + β)Z_L and Z_o = (R_S + r_π)/(1 + β)

Solution: https://www.youtube.com/watch?v=UH5_EioJdxU


9. In the circuit shown, assume that the OP-AMP is ideal.

a. Obtain an expression for V_o in terms of V_s, R and the reverse saturation current I_s of the transistor.
b. If R = 1 Ω, I_s = 1 pA and the thermal voltage V_T = 25 mV, then what is the value of the output voltage V_o for an input voltage V_s of 1 volt?
c. Suppose that the transistor in the feedback path is replaced by a PN junction diode with a reverse saturation current of I_s. The P-side of the diode is connected to node A and the N-side to node B. then what is the expression for V_o in terms of V_s, R and I_s ?

Answer:
(a) V_O = – V_T ln(V_S/I_OR)
(b) – 0.81 volts
(c) V_O = – ηV_T ln(V_S/I_OR)

Solution: https://www.youtube.com/watch?v=3YOkRQGOWbg

GATE 2001 ECE Video Solution on Digital Circuits (Digital Electronics)

1. The 2’s complement representation of – 17 is
a. 01110
b. 101111
c. 11110
d. 10001

Answer:B

Solution : https://www.youtube.com/watch?v=6SQjwYET7cM


2. For the ring oscillator shown in teh figure, the propagation delay of each inverter is 100 pico sec. What is the fundamental frequency of the oscillator output?

a. 10 MHz
b. 100 MHz
c. 1 GHz
d. 2 GHz

Answer:C

Solution : https://www.youtube.com/watch?v=HefE3DzUfOo


3. An 8085 microprocessor based system uses a 4K x8 bit RAM whose starting address is AA00H. The address of the last byte in this RAM is
a. 0FFFH
b. 1000H
c. B9FFH
d. BA00H

Answer:C

Solution : https://www.youtube.com/watch?v=psL4GimAjV8


4. In the figure, the LED

a. Emits light when both S₁ and S₂ are closed.
b. Emits light when both S₁ and S₂ are open.
c. Emits light when only of S₁ or S₂ is closed.
d. Does not emit light, irrespective of the switch positions.

Answer:D

Solution : https://www.youtube.com/watch?v=XqDoyQ5IirY


5. In the TTL circuit in the figure, S₂ to S₀ are select lines and X₇ to X₀ are input lines. S₀ and X₀ are LSBs. The output Y is

Answer:D

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


6. The digital block in the figure, realized using two positive edge triggered D flip-flops. Assume that for t<t₀, Q₁ = Q₂ =0. The circuit in the digital block is given by

Answer:C

Solution : https://www.youtube.com/watch?v=gkkCKeFhQ-s


7. In the DRAM cell in the figure is the V_T of the N-MOSFET is 1 volt. For the following three combinations of WL and BL voltages.

a. 5V; 3V; 7V
b. 4V; 3V; 4V
c. 5V; 5V; 5V
d. 4V; 4V; 4V

Answer:B

Solution : https://www.youtube.com/watch?v=o_B29MzGFPU


8. A monochrome video signal that ranges from 0 to 8 volts is digitized using an 8-bit ADC.
a. Determine the resolution of the ADC in V/bit.
b. Calculate the mean squared quantization error.
c. Suppose the ADC is counter controlled. The counter is up counter and positive edge triggered with clock frequency 1 MHz. What is the time taken in seconds to get a digital equivalent of 1.59 volts?

Solution : https://www.youtube.com/watch?v=ZI8JkuF3PNQ


9. In the figure, the output of the oscillator, V₁ has 10 volts peak amplitude with zero DC value. The transfer characteristic of the Schmitt inverter is also shown in the figure. Assume that the JK flip-flop is reset at time t=0.

a. What is the period and duty cycle of the waveform V₂?
b. What is the period and duty cycle of the waveform V₃?
c. Sketch V₁, V₂ and V₃ for the duration 0 ≤ t ≤ 6 µsec. Clearly indicate the exact timings when the waveforms V₂ and V₃ make high to low and low to high transitions.

Solution : https://www.youtube.com/watch?v=Gr8CESH_ZJM


10. For the digital block shown in the figure, the output Y = f(S₃,S₂,S₂,S₀), where S₃ is MSB and S₀ is LSB. Y is given in terms of minterms as Y = Σm(1,5,6,7,11,12,13,15) and its complement is given as Σm(0,2,3,4,8,9,10,14).

a. Enter the logical values in the given Karnaugh map in the figure, for the output Y.
b. Write down the expression for Y in sum of products form using minimum number of terms.
c. Draw the circuit for the digital logic boxes using four 2 input NAND gates only for each of the boxes.

Solution : https://www.youtube.com/watch?v=4ERh7YV3nKE


11. Consider the following sequence of instructions for an 8085 microprocessor based system.

a. If the program execution begins at the location FF00H, write down the sequence of instructions which are actually executed till a HLT instruction. Assume all Flags are initially RESET.
b. Which of the three ports (PORT1, PORT2 and PORT3) will be loaded with data, and what is the bit pattern of the data?

Solution :

GATE 2001 ECE Video Solutions on EDC (Electronic Devices and Circuits)

1. MOSFET can be used as a
a. Current controlled capacitor
b. Voltage controlled capacitor
c. Current controlled inductor
d. Voltage controlled inductor

Answer: B

Solution : https://www.youtube.com/watch?v=DYvtwvbyh8Q


2. The effective channel length of a MOSFET in saturation decreases with increase in
a. Gate voltage
b. Drain voltage
c. Source voltage
d. Body voltage

Answer: B

Solution : https://www.youtube.com/watch?v=yySAOIv7hiw


3. The transistor shunt regulator shown in figure has a regulated output voltage of 10 volts, when input varies from 20 volts to 30 volts. The relevant parameters for the zener diode and the transistor are: V_Z = 9.5 volts, V_BE = 0.3 votls, β = 99. Neglect the current throught R_B. Then the maximum power dissipated in the zener diode (P_Z) and the transistor (P_T) are

Answer: C

Solution : https://www.youtube.com/watch?v=1byJ9jdLUHc


4. For the circuit shown in figure, D₁ and D₂ are identical diodes with ideality factor of unity. The thermal voltage V_T = 25 mV.
a. If the reverse saturation current, I_S, for the diode is 1 pA, then compute the current I through the circuit.
b. Calculate V_f and V_r.

Answer: (a) 1 pA (b) 0.018 mV and 0.032 mV

Solution : https://www.youtube.com/watch?v=cK8_pacEAZY