GATE 2014 Video Solutions (Analog Circuits) (all 4 sets)

Set – 1 (15th February 2014 (Forenoon))

1.       In the figure, assume that the forward voltage drops to the PN diode D₁ and Schottky diode D₂ are 0.7 volts and 0.3 volts respectively. If ON denotes conducting state of the diode and OFF denotes the non conducting state of the diode, then in the circuit,

a.       Both are ON

b.      D₁ is ON and D₂ is OFF

c.       Both are OFF

d.      D₁ is OFF and D₂ is ON

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

2.       A good current buffer has

a.       Low input impedance and low output impedance

b.      Low input impedance and high output impedance

c.       high input impedance and low output impedance

d.      high input impedance and high output impedance

               Solution :    https://www.youtube.com/watch?v=vdYmByP9zYY

3.       In the ac equivalent circuit shown in the figure, if i_in is the input current and R_F is very large, then the type of feedback is 

a.       Voltage – Voltage feedback

b.      Voltage – Current feedback

c.       Current – Voltage feedback

d.      Current – Current feedback

               Solution :    https://www.youtube.com/watch?v=otvYW4oudRg

4.       In the low pass filter shown in the figure, for a cutoff frequency of 5 KHz, the value of R₂ (in KΩ) is ……..

 

         

               Solution :    https://www.youtube.com/watch?v=BjcHUWQA4TQ

5.       A BJT is biased in forward active mode. Assume V_BE = 0.7 volts, KT/q = 25 mV and reverse saturation current I_S = 10^-13 Amp. The Transconductance of the BJT (in mA/volt) is…..

               Solution :    https://www.youtube.com/watch?v=nAh0aTdVp84

6.       In the voltage regulator circuit shown in the figure, the Op-Amp is ideal. The BJT has V_BE = 0.7 volts, and β = 100, and the zener voltage is 4.7 volts. For a regulated output of 9 volts, the value of R (in Ω) is ……..

 

              

               Solution :   https://www.youtube.com/watch?v=B5rropdO8jA

7.       In the circuit shown, the Op-Amp has finite input resistance, infinite voltage gain and zero input offset voltage. The output voltage V_out is …….

 a.       – I₂(R₁ + R₂)

b.      I₂R₂

c.       I₁R₂

d.      – I₁(R₁ + R₂)

               Solution :   https://www.youtube.com/watch?v=DAEuj8Z-ncY

8.       For the amplifier shown in the figure, the BJT parameters are V_BE = 0.7 volts, β = 200, and thermal voltage V_T = 25 mV. The voltage gain (v_o/v_i) of the amplifier is ……..

 

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

SET – 2 (15th February 2014 (Afternoon))

1.       The diode in the circuit shown, if V_on = 0.7 volts but is ideal otherwise. If V_i = 5 sin(ωt) volts, the minimum and maximum values of V_o (in volts) are, respectively,

 a.       -5 and 2.7

b.      2.7 and 5

c.       -5 and 3.85

d.      1.3 and 5

               Solution :    https://www.youtube.com/watch?v=VNI1bsbW2i8

2.       The feedback topology in the amplifier circuit (the base bias circuit is not shown for simplicity) in the figure is 

a.       Voltage – Shunt feedback

b.      Current – Series feedback

c.       Current – Shunt feedback

d.      Voltage – Series feedback

               Solution :   https://www.youtube.com/watch?v=MNduRhMC6zk

3.       In the differential amplifier shown in the figure, the magnitude of the common mode and differential mode gains are A_cm and A_d, respectively. If the resistance R_E is increased, then

a.       A_cm increases

b.      Common mode rejection ratio increases

c.       A_d increases

d.      Common mode rejection ratio decreases

               Solution :   https://www.youtube.com/watch?v=AhxODnKBU5Y

4.       A cascade connection of two voltage amplifiers A1 and A2 is shown in the figure. The open loop gain A_vo, input resistance R_in, and output resistance R_o for A1 and A2 are as follows:

A1 : A_vo = 10,   R_in = 10 KΩ,   R_o = 1 KΩ

A2 : A_vo = 5,     R_in = 5 KΩ,      R_o = 200 Ω

                       The approximate overall voltage gain V_out / V_in is …………….

Solution :   https://www.youtube.com/watch?v=ijiC9w_XNuw

SET – 3  (16th February 2014 (Forenoon))

1.       In the circuit shown, the PNP transistor has |V_BE| = 0.7 volts and β = 50. Assume that R_B = 100 KΩ. For V_o to be 5 volts, the value of R_C (in KΩ) is ……..

 

               Solution :    https://www.youtube.com/watch?v=ohf5m4r0gzs

2.       The desirable characteristics of a Transconductance amplifier are

a.       High input resistance and High output resistance

b.      High input resistance and Low output resistance

c.       Low input resistance and High output resistance

d.      Low input resistance and Low output resistance

               Solution :   https://www.youtube.com/watch?v=1RsZ43lyRhs

3.       The figure shows a half wave rectifier. The diode D is ideal. The average steady state current (in Amperes) through the diode is approximately…………

 

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

4.       Assuming that the Op-Amp in the circuit is ideal, then the output voltage is

 

               Solution :   https://www.youtube.com/watch?v=Q7DUP4Rz58o

5.       In the circuit shown, the silicon BJT has β = 50. Assume V_BE = 0.7 volts and V_CEsat = 0.2 volts. Which one of the following statements is correct?

a.       For R_C = 1 kΩ, the BJT operates in the saturation region

b.      For R_C = 3 kΩ, the BJT operates in the saturation region

c.       For R_C = 20 kΩ, the BJT operates in the cutoff region

d.      For R_C = 20 kΩ, the BJT operates in the linear region

               Solution :    https://www.youtube.com/watch?v=zd_NFD2CN8E

SET  - 4  (16th February 2014 (Afternoon))

 

1.       If the emitter resistance in a common emitter voltage amplifier is not bypassed, it will

a.       Reduce both the voltage gain and the input impedance

b.      Reduce the voltage gain and increase the input impedance

c.       Increase the voltage gain and reduce the input impedance

d.      Increase both the voltage gain and the input impedance

               Solution :    https://www.youtube.com/watch?v=4YjclPDw5lM

2.       Consider two BJTs biased at the same collector current with area A₁ = 0.2 µm x 0.2 µm and A₂ = 300 µm x 300 µm. assuming that all other device parameters are identical, KT/q = 26 mV, the intrinsic carrier concentration is 1 x 10¹⁰ cm^-3, and q = 1.6 x 10^-19C, the difference between the base emitter voltages (in mV) of the two BJTs (i.e. V_BE1 – V_BE2) is …………….

               Solution :    https://www.youtube.com/watch?v=R-GogUWvN74

3.       A BJT in a common base configuration is used to amplify a signal received by a 50Ω antenna. Assume KT/q = 25 mV, the value of collector bias current (in mA) required to match the input impedance of the amplifier to the impedance of the antenna is ………..

               Solution :    https://www.youtube.com/watch?v=HBjqJb91WbE

4.       Two silicon diodes, with a forward voltage drop of 0.7 volts, are used in the circuit shown in the figure. The range of input voltage Vi for which the output voltage Vo = Vi, is

a.       -0.3 volts < Vi  < 1.3 volts

b.      -0.3 volts < Vi  < 2 volts

c.       -1.0 volts < Vi  < 2.0 volts

d.      -1.7 volts < Vi  < 2.7 volts

               Solution :  https://www.youtube.com/watch?v=6GsjQs9DKbU

5.       The circuit represents 

 a.       A band pass filter

b.      A voltage controlled oscillator

c.       An Amplitude modulator

d.      A monostable multivibrator

               Solution :  https://www.youtube.com/watch?v=oi_nPP2yd4k

6.       Consider the common collector amplifier in the figure (bias circuitry ensures that the transistor operates in forward active region, but has been omitted for simplicity). Let I_C be the collector current, V_BE be the base emitter voltage and V_T be the thermal voltage. Also, g_m and r_o are the small signal Transconductance and output resistance of the transistor, respectively. Which one of the following conditions ensures a nearly constant small signal voltage gain for a wide range of values of R_E?

 

           

               Solution :  https://www.youtube.com/watch?v=Xur5bWVoR10

7.       For the common collector amplifier shown in the figure, the BJT has high β, negligible V_CEsat and V_BE = 0.7 volts. The maximum undistorted peak to peak output voltage V_o (in volts) is ………

                 Solution :  https://www.youtube.com/watch?v=LsXNjgHVeK0