July 2014 | GATE 2023 - Important Concepts, Short cuts, Complete Solutions, Examples and Practice Problems

GATE 2008 ECE Video Solutions on Analog Circuits (Analog Electronics)

1. Consider the following circuit using an ideal OP-AMP. The I-V characteristic of the diode is described by the relation I = I_o(exp(V/V_T) - 1), where VT = 25 mV, I_o = 1 µA and V is the voltage across the diode(taken as positive for forward bias). For an input voltage V_i = - 1 volts, the output voltage V_o is

a. 0 volts
b. 0.1 volts
c. 0.7 volts
d. 1.1 volts

Solution: https://www.youtube.com/watch?v=Hm-AQGstHH0

2. The OP-AMP circuit shown below represents a

a. High pass filter
b. Low pass filter
c. Band pass filter
d. Band reject filter

Solution: https://www.youtube.com/watch?v=iNclgQhX8gs

3. Consider the schmitt trigger circuit shown below.

A triangular wave which goes from –12 volts to +12 volts is applied to the inverting input of OP-AMP. Assume that the output of the OP-AMP swings from +15 volts to –15 volts. The voltage at the non-inverting input switches between
a. – 12 volts and +12 volts
b. – 7.5 volts and +7.5 volts
c. – 5 volts and +5 volts
d. 0 volts and +5 volts

Solution: https://www.youtube.com/watch?v=U1PM8Q0IT0o

Statement for Linked Answer Question:
In the following transistor circuit, V_BE = 0.7 volts, r_e = 25 mV/I_E, β and all the capacitances are very large.

4. The value of DC current I_E is
a. 1 mA
b. 2 mA
c. 5 mA
d. 10 mA

5. The mid-band voltage gain of the amplifier is approximately
a. – 180
b. – 120
c. – 90
d. – 60

Solution(4 & 5): https://www.youtube.com/watch?v=eX0es1gFdW4

GATE 2009 ECE Video Solutions on Analog Circuits (Analog Electronics)

1. In the following Astable Multivibrator circuit, which properties of V_o(t) depend on R₂ ?

a. Only the frequency
b. Only the amplitude
c. Both the amplitude and the frequency
d. Neither the amplitude nor the frequency

Solution: https://www.youtube.com/watch?v=CNrhstw1lQI

2. In the circuit shown below, the OP-AMP is ideal, the transistor has V_BE = 0.6 volts and β = 150. Decide whether the feedback in the circuit is positive or negative and determine the voltage V at the output of the OP-AMP.

a. Positive feedback, V = 10 Volts
b. Positive feedback, V = 0 Volts
c. Negative feedback, V = 5 Volts
d. Negative feedback, V = 2 Volts

Solution: https://www.youtube.com/watch?v=H6FpEgr7ZYI

3. A small signal source Vi(t) = Acos20t + Bsin10⁶t is applied to a transistor amplifier as shown below. The transistor has β = 150 and h_ie = 3 KΩ. Which expression best approximate V_o(t).

a. V_o(t) = - 1500 (Acos20t + Bsin10⁶t)
b. V_o(t) = - 150 (Acos20t + Bsin10⁶t)
c. V_o(t) = - 1500 (Bsin10⁶t)
d. V_o(t) = - 150 (Bsin10⁶t)

Solution: https://www.youtube.com/watch?v=C-1mKYDJhY4

GATE 2010 ECE Video Solutions on Analog Circuits (Analog Electronics)

1. The amplifier circuit shown below uses a silicon transistor. The capacitors C_C and C_E can be assumed to be short at signal frequency and effect of output resistance r_o can be ignored. If C_E is disconnected from the circuit, which one of the following statements is TRUE.

a. The input resistance R_i increases and magnitude of voltage gain A_V decreases
b. The input resistance R_i decreases and magnitude of voltage gain A_V increases
c. The input resistance R_i decreases and magnitude of voltage gain A_V decreases
d. The input resistance R_i increases and magnitude of voltage gain A_V increases

Solution: https://www.youtube.com/watch?v=E48_Y4CYKIU

2. In the silicon BJT circuit shown below, assume that the emitter area of transistor Q₁ is half that of transistor Q₂. The value of current I_o is approximately

a. 0.5 mA
b. 2 mA
c. 9.3 mA
d. 15 mA

Solution: https://www.youtube.com/watch?v=jWdra3gmHK0

3. Assuming the OP-AMP is ideal, the voltage gain of the amplifier shown below is

a. - R₂/R₁
b. - R₃/R₁
c. - (R₂ || R₃) / R₁
d. - (R₂ + R₃)/R₁

Solution: https://www.youtube.com/watch?v=-GMfvkT72y0

4. The transfer characteristic for the precision rectifier circuit shown below is (Assume ideal OP-AMP and Practical Diodes)

Solution: https://www.youtube.com/watch?v=K2Rp0dv6Ll0

Common Data Questions:
Consider the common emitter amplifier shown below with the following circuit parameters.
β = 100, g_m = 0.3861 A/V, r_o = 259 Ω, R_S = 1 KΩ, R_B = 93 KΩ, R_C = 250 Ω, R_L = 1 KΩ, C₁ = ∞ and C₂ = 4.7 µF.

5. The resistance seen by the source V_S is
a. 258 Ω
b. 1258 Ω
c. 93 KΩ
d. ∞

6. The lower cutoff frequency due to C₂ is
a. 33.9 Hz
b. 27.1 Hz
c. 13.6 Hz
d. 16.9 Hz

Solution: https://www.youtube.com/watch?v=FdpAV2BR7Fc

GATE 2011 ECE Video Solutions on Analog Circuits (Analog Electronics)

1. In the circuit shown below, capacitors C₁ and C₂ are very large and are shorts at the input frequency . v_i is a small signal input. The gain magnitude |V₀/V_i| at 10 M rad/sec is

a. Maximum
b. Minimum
c. Unity
d. Zero

Solution: https://www.youtube.com/watch?v=OL8a4oM3MhM

2. The circuit below implements a filter between the input current i_i and the output voltage v_o. Assume that the op-amp is ideal. The filter implemented is a

a. Low pass filter
b. Band pass filter
c. Band stop filter
d. High pass filter

Solution: https://www.youtube.com/watch?v=jH8CXKYc1No

Statement for linked answer Questions (3 and 4):
In the circuit shown below, assume that the voltage drop across a forward biased diode is 0.7 votls. The thermal voltage V_T = KT/q = 25 mV. The small signal input v_i = 100 cos(ωt) mV.

3. The bias current I_DC through the diodes is
a. 1 mA
b. 1.28 mA
c. 1.5 mA
d. 2 mA

4. The ac output voltage V_AC is
a. 0.25 cos(ωt) mV
b. 1 cos(ωt) mV
c. 2 cos(ωt) mV
d. 22 cos(ωt) mV

Solution: https://www.youtube.com/watch?v=s3I6VcArveo

GATE 2012 ECE Video Solutions on Analog Circuits (Analog Electronics)

1. The current i_b through the base of a silicon NPN transistor is 1+0.1cos (10000πt) mA. At 300^oK, the r_π in the small signal model of the transistor is ________ (in Ohms).