GATE 2000 ECE Video Solutions on Analog Circuits (Analog Electronics)

1. In the differential amplifier of the figure, if the source resistance of the current source I_EE is infinite, then the common mode gain is

a. Zero
b. Infinite
c. Indeterminate
d. (V_in1 + V_in2) / 2V_T

Answer: A

Solution: https://www.youtube.com/watch?v=goC-ZRrr_Yw


2. In the circuit shown in figure, the output voltage V_o is

a. – 1 volts
b. 2 volts
c. + 1 volts
d. + 15 volts

Answer: D

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


3. Introducing a resistor in the emitter of a CE amplifier stabilizes the dc operating point against variations in
a. Only the temperature
b. Only the β of the transistor
c. Both temperature and β
d. None of the above

Answer: C

Solution: https://www.youtube.com/watch?v=Hj4RgZDwBwk


4. The current gain of a bipolar transistor drops at high frequencies because of
a. Transistor capacitances
b. High current effects in the base
c. Parasitic inductance effects
d. The Early Effect

Answer: A

Solution: https://www.youtube.com/watch?v=mZE9xTPfxjs


5. If the OP-AMP in the figure is ideal, then the output voltage V_o is

a. Zero
b. (V₁ – V₂) sinωt
c. – (V₁ + V₂) sinωt
d. (V₁ + V₂) sinωt

Answer: C

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


6. The configuration of the figure is a

a. Precision rectifier
b. Hartley oscillator
c. Butterworth high pass filter
d. Wien-bridge oscillator

Answer: D

Solution: https://www.youtube.com/watch?v=PxZImxr0h6Q


7. Assume that the OP-AMP of the figure is ideal. If V_i is a triangular wave, then V_o will be

a. Square wave
b. Triangular wave
c. Parabolic wave
d. Sine wave

Answer: A

Solution: https://www.youtube.com/watch?v=ZvsEb1Tpxaw


8. The most commonly used amplifier in Sample and Hold circuits is
a. Unity gain inverting amplifier
b. Unity gain non-inverting amplifier
c. An inverting amplifier with a gain of 10
d. An inverting amplifier with a gain of 100

Answer: B

Solution: https://www.youtube.com/watch?v=JFfOcIr8x7U


9. If the OP-AMP in the figure has an input offset voltage of 5 mV and an open loop voltage gain of 10,000. Then the output V_o will be

a. 0 volts
b. 5 mV
c. + 15 volts or – 15 volts
d. + 50 volts or – 50 volts

Answer: C

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


10. a. For the circuit shown, plot V_o under steady state conditions, with and without capacitor C. Assume that the diode is ideal.

Answer: With Capacitor, circuit acts as Envelope Detector and With out capacitor, circuit acts as clipper which clips negative half cycle.

Solution: https://www.youtube.com/watch?v=GJXs26_62eE

b. Design a circuit using two ideal diodes, one resistor and two voltage sources that would convert the input voltage to the output voltage as shown in figure. The resistor value need not be specified.

Answer:

Solution: https://www.youtube.com/watch?v=gXD0ms6S8iY


11. For the amplifier circuit shown, I_C = 1.3 mA, R_C = 2 kΩ, R_E = 500 Ω, V_T = 26 mV, β = 100, V_CC = 15 volts, V_S = 0.01 sin(ωt) volts and C_b = C_e = 10 µF.

a. What is the small signal voltage gain, V_o/V_S
b. What is the approximate voltage gain if C_e is removed?
c. What will be the output Vo, if C_b is short circuited?

Answer: (a) -100, (b) -4, (c) - sinwt

Solution: https://www.youtube.com/watch?v=x75WPMXrTOg


12. For a feedback amplifier, the open loop transfer function has three poles at 100 k rad/sec, 1 M rad/sec and 10 M rad/sec. The low frequency open loop gain is 1000 and the feedback factor (β) is 1. Use Bode plots to determine the phase margin of the amplifier. Is the amplifier stable?

Solution: Amplifier is Unstable.


13. Below figure shown is a common base amplifier.

a. Write expressions for the time constants associated with the capacitances C_b and C_s.
b. What is the approximate lower cutoff frequency of the amplifier?

Answer:
τ_Cb = 2π(r_e + R_E//R_S),
τ_Cs = 2π(r_e//R_E +R_S)C_S,
f_Cb = 1/τ_Cb , f_Cs = 1/ τ_Cs ,
overall fL = Max{ f_Cb , f_Cs }

Solution: https://www.youtube.com/watch?v=wTtlORiy598

GATE 2000 ECE Video Solution on Digital Circuits (Digital Electronics)

1. The number of comparators in a 4 bit flash ADC is
a. 4
b. 5
c. 15
d. 16

Answer:C

Solution : https://www.youtube.com/watch?v=N8JKcDEFZOU


2. For the logic circuit shown in the figure, the required input combination (A,B,C) to make the output X = 1 is


a. 1, 0, 1
b. 0, 0, 1
c. 1, 1, 1
d. 0, 1, 1

Answer:D

Solution : https://www.youtube.com/watch?v=XdpX7qOFqBM


3. In the 8085 microprocessor, the RST 6 instruction transfers the program execution to the following location
a. 30H
b. 24H
c. 48H
d. 60H

Answer:A

Solution : https://www.youtube.com/watch?v=48roVRL_x1o


4. An 8 bit successive approximation analog to digital converter has full scale reading of 2.55 volts and its conversion time for an anlog input of 1 volt is 20 µs. The conversion time for a 2 volts input is
a. 10 µs
b. 20 µs
c. 40 µs
d. 50 µs

Answer:B

Solution : https://www.youtube.com/watch?v=p_-ta5fKctI


5. The number of hardware interrupts (which require an external signal to interrupt) present in an 8085 microprocessor are
a. 1
b. 4
c. 5
d. 13

Answer:C

Solution : https://www.youtube.com/watch?v=Wt1abwe4das


6. The most commonly used amplifier in sample and hold circuits is
a. A unity gain inverting amplifier
b. A unity gain non inverting amplifier
c. An inverting amplifier with a gain of 10
d. An inverting amplifier with a gain of 100

Answer:B

Solution : https://www.youtube.com/watch?v=JFfOcIr8x7U


7. For the logic circuit shown, the simplified Boolean expression for the output Y is

a. A + B + C
b. A
c. B
d. C

Answer:C

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


8. For the 4 bit DAC shown, the output voltage V_o is

a. 10 volts
b. 5 volts
c. 4 volts
d. 8 volts

Answer:B

Solution : https://www.youtube.com/watch?v=6MeSzmvu4MU


9. A sequential circuit using D flip flop and logic gates is shown in figure, where X and Y are the inputs and Z is output. The circuit is

a. S-R flip flop with inputs X = R and Y = S
b. S-R flip flop with inputs X = S and Y = R
c. J-K flip flop with inputs X = J and Y = K
d. J-K flip flop with inputs X = K and Y = J

Answer:D

Solution : https://www.youtube.com/watch?v=Z9naO48RJT8


10. The contents of register (B) and Accumulator (A) of 8085 microprocessor are 49H and 3AH respectively. The contents of A and the status of carry flag (CY) and sign flag (S) after executing SUB B instruction are
a. A = F1 , CY = 1 , S = 1
b. A = 0F, CY = 1, S = 1
c. A = F0, CY = 0, S = 0
d. A = 1F, CY = 1, S = 1

Answer:A

Solution : https://www.youtube.com/watch?v=G08SPzuh2Lk


11. In the given figure, the J and K inputs of all the four flip-flops are made high. The frequency of the signal at output Y is

a. 0.833 KHz
b. 1.0 KHz
c. 0.91 KHz
d. 0.77 KHz

Answer:B

Solution : https://www.youtube.com/watch?v=ed2xKY4lc2c


12. For the CMOS monostable multivibrator of given figure, R = 50 KΩ and C = 0.01 µF, V_DD = 5 volts, and the CMOS NOR gates have a threshold voltage (V_T) of 1.5 volts. V_in is a trigger pulse (τ_p << RC) as shown in the figure.

a. Plot V_A1 and V_o1 as functions of time.
b. Write the equation for V_R(t), for t > 0
c. Find the time period of the output pulse.

Solution : https://www.youtube.com/watch?v=qeQX32IB7iQ


13. The operating conditions (ON = 1 and OFF = 0) of three pumps (x, y, z) are to be monitored, x = 1 implies that pump x is on. It is required that the indicator (LED) on the panel should glow when a majority of the pumps fail.

a. Enter the logical values in the K map in the format shown in figure. Derive the minimal Boolean sum of products expression whose output is zero when a majority of the pumps fail.
b. The above expression is implemented using logic gates, and point P is the output of the circuit, as shown in given figure, P is at 0 volts when a majority of the pumps fails and is at 5 volts otherwise. Design a circuit to derive the LED using this output.
The current through the LED should be 10 mA and the voltage drop across it is 1 volt. Assume that P can source or sink 10 mA and a 5 volts supply is available.

Solution : https://www.youtube.com/watch?v=F-sbnjhbHec


14. A one bit full adder is to be implemented using 8 to 1 multiplexers (MUX).
a. Write the truth table for sum (S) and carry to the next stage (C_N), in terms of the two bits (A, B) and the carry from the previous stage (C_P). The truth table should be in the ascending order of (A, B, C_P) i.e. (000, 001, 010..... etc).
b. Implement S and C_N using 8 to 1 multiplexers.

Solution : https://www.youtube.com/watch?v=1WaxJ9TChns


15. The program and machine code for an 8085 microprocessor are given by
The starting address of the above program is 7FFFH. What would happen if it is executed from 8000H?


Solution :

GATE 2000 ECE Video Solutions on EDC (Electronic Devices and Circuits)

1. For the circuit in figure shown, the voltage V_o is

a. 2 volts
b. 1 volts
c. -1 volts
d. None of the above

Answer: D

Solution : https://www.youtube.com/watch?v=wtNGel7O7ic


2. In circuit shown, assume that the transistor is in active region. It has a large β and its base emitter voltage is 0.7 volts. The value of I_C is

a. Indeterminate since R_C is not given
b. 1 mA
c. 5 mA
d. 10 mA

Answer: B

Solution : https://www.youtube.com/watch?v=h1mXFKwlnbQ