Previous GATE Questions on Transistor Biasing (1987 - Till Date)

1989

1.       Of the four biasing circuits shown in figure, for a BJT, indicate the one which can have maximum bias stability

Answer:    A

   Solution :   https://www.youtube.com/watch?v=yvA3x-0ljUo           

1990

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           

1991

1.       In figure, both transistors are identical and have a high value of β. Take the DC base emitter voltage drop as 0.7 volts and KT/q = 25 mV. The small signal low frequency voltage gain (V_o/V_i) is equal to __________

  Answer:   120

   Solution:   https://www.youtube.com/watch?v=u_bD4jaVEY4

1992

1.       If the transistors in figure, have high values of β and a V_BE of 0.65 volts, the current I flowing through the 2 KΩ resistance will be…………

 

Answer:           A       

     Solution :  https://www.youtube.com/watch?v=kFEVs7bXj9M

1993

1.       α – cutoff frequency of a bipolar junction transistor

         a.       increases with the increase in base width

         b.      increases with the increase in emitter width

         c.       increase with increase in the collector width

         d.      increase with decrease in the base width

Answer:   D

   Solution :     https://www.youtube.com/watch?v=7w55H7EAs_Q

2.       In a multistage RC coupled amplifier, the coupling capacitor

         a.       limits the low frequency response

         b.      limits the high frequency response

         c.       does not affect the frequency response

         d.      blocks the DC component without affecting the frequency response

Answer:   A

   Solution :    https://www.youtube.com/watch?v=vaO9XM_q8SQ

3.       The bandwidth of an n-stage tuned amplifier, with each stage having a bandwidth of B, is given by

  

Answer:   C

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

1994

1.  In the common emitter amplifier shown, the transistor has a forward current gain of 100, and a base to emitter voltage of 0.6 volts. Assume I_CO to be negligible. Choose value for R₁ and R₃ such that the transistor has a collector current of 1 mA and a collector to emitter voltage of 2.5 volts.

Answer:   41 kΩ and 2.2 kΩ
      Solution :    https://www.youtube.com/watch?v=SjV5f5WC8GU

1995

1.       An RC coupled amplifier is assumed to have a single pole low frequency transfer function. The maximum lower cutoff frequency allowed for the amplifier to pass 50 Hz square wave with no more than 10% tilt is ______________

Answer:   150 Hz

             Solution :  https://www.youtube.com/watch?v=Y7Pez6ot4bQ

2.       A BJT is said to be operating in the saturation region, if

            a.       Both the junctions are reverse biased

            b.      Base emitter junction is in reverse biased, and base collector junction is forward biased

            c.       Base emitter junction is in forward biased, and base collector junction is reverse biased

            d.      Both the junctions are forward biased

Answer:   D

                 Solution :   https://www.youtube.com/watch?v=vafpJ7FB9xE

3.   A transistor having α = 0.99 and V_BE = 0.7 volts, in the circuit shown, then the value of the collector current will be…………

 

Answer:   3.725 mA

                Solution :   https://www.youtube.com/watch?v=2SJ3DMImgPk

4.   The circuit shown in figure, supplies power to an 8 Ω loud speaker. The values of I_C and V_CE for this circuit will be

Answer:   3.4 Amp and 16.4 Volts

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

1996

1.     If a transistor is operating with both of its junctions forward biased, but with the collector base forward bias greater than the emitter base forward bias, then it is operating in the

            a.       Forward active mode

            b.      Reverse active mode

            c.       Reverse saturation mode

            d.      Forward saturation mode

Answer:   C

                  Solution :   https://www.youtube.com/watch?v=4MkPYKEIJ2Y

1997

1.     In the cascade amplifier circuit shown, determine the values of R₁, R₂ and R_L such that the quiescent current through the transistors is 1 mA and the collector voltages are V_C1 = 3 volts, and V_C2 = 6 volts. Take V_BE = 0.7 volts and assume β of the transistors is very high and base currents to be negligible. 

Answer:   59 kΩ, 31 kΩ, 3 kΩ

                  Solution :  https://www.youtube.com/watch?v=rAgjdD4Zhrg

2000

1.     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

2002

1.       If the transistor in figure is in saturation, then

 

Answer:   D

             Solution :  https://www.youtube.com/watch?v=eGQmSi1Xdxk

2004

1.       If for a silicon NPN transistor, the base to emitter voltage (V_BE) is 0.7 volts and collector to base voltage (V_CB) is 0.2 volts, then the transistor is operating in the

            a.       Normal active mode

            b.      Saturation mode

            c.       Inverse active mode

            d.      Cutoff mode

Answer:   A

               Solution :  https://www.youtube.com/watch?v=EWiTi5LriHE

2.       Assuming V_CEsat = 0.2 volts and β = 50, the minimum base current (I_Bmin) required to drive the transistor in figure to saturation is

 

Answer:   A

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

3.   Assuming that the β of the transistor is extremely large and V_BE = 0.7 volts, I_C and V_CE in the circuit shown are

 

Answer:   C

                Solution : https://www.youtube.com/watch?v=ETrg3InTVmY

2005

1.         For an NPN transistor connected as shown in figure, V_BE = 0.7 volts. Given that reverse saturation current of the junction at room temperature 300^oK is 10^-13 amp, the emitter current is 

         a.       30 mA

         b.      39 mA

         c.       49 mA

         d.      20 mA

Answer:    C
Solution:  https://www.youtube.com/watch?v=3HVbE9qCcH8

2.       The circuit using a BJT with β = 50 and V_BE = 0.7 volts is shown in figure. The base current I_B and the collector voltage V_C are respectively.

         a.       43 µA and 11.4 volts

         b.      40 µA and 16 volts

         c.       45 µA and 11 volts

         d.      50 µA and 10  volts

Answer:   B
Solution:  https://www.youtube.com/watch?v=W8VHHTLp6Kg

2006

Common Data for Questions (1,2 and 3):

In the transistor amplifier circuit shown in the figure below, the transistor has the following parameters: β_DC = 60, V_BE = 0.7 volts, h_ie -> ∞, h_oe -> ∞. The capacitance C_C can be assumed to be infinite.

 1.       Under the DC conditions, the collector to emitter voltage drop is

         a.       4.8 volts 

         b.      5.3 volts

         c.       6.0 volts

         d.      6.6 volts

Answer:   C

2.       If β_DC  is increased by 10%, the collector to emitter voltage drop

         a.       Increases by less than or equal to 10%

         b.      Decreases by less than or equal to 10%

         c.       Increases by more than 10%

         d.      Decreases by more than 10%

Answer:   B

3.       The small signal gain of the amplifier V_o/V_s is

         a.       – 10

         b.      – 5.3

         c.       + 5.3

         d.      + 10

Answer:  A   

Solution:  https://www.youtube.com/watch?v=qdpEHlqob00

2007

1.       For the BJT circuit shown, assume that the β of the transistor is very large and V_BE is 0.7 volts. The mode of operation of the BJT is 

            a.       Cut off

            b.      Saturation

            c.       Normal active

            d.      Inverse active

Answer:   B

               Solution :  https://www.youtube.com/watch?v=iXf86EM2YOM

2008

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.

 1.       The value of DC current I_E is

         a.       1 mA

         b.      2 mA

         c.       5 mA

         d.      10 mA

Answer:  A

2.       The mid-band voltage gain of the amplifier is approximately

         a.       – 180

         b.      – 120

         c.       – 90

         d.      – 60

Answer:   D 
Solution: https://www.youtube.com/watch?v=eX0es1gFdW4

2011

1.     For a BJT, the common base current gain α = 0.98 and the collector base junction reverse bias saturation current, I_CO = 0.6 µA. This BJT is connected in the common emitter mode and operated in the active region with a base current (I_B) of 20 µA. The collector current I_C for this mode of operation is

            a.       0.98 mA

            b.      0.99 mA

            c.       1.0 mA

            d.      1.01 mA

Answer:   D

               Solution : https://www.youtube.com/watch?v=V103i22HX0Y

2013

1.      In the circuit shown below, the silicon NPN transistor Q has a very high value of β. The required value of R₂ in KΩ to produce I_C = 1 mA is 

 

         a.       20

         b.      30

         c.       40

         d.      50

Answer:   C

https://www.youtube.com/watch?v=seLmVm94TqY

2014

1.       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…..

Answer:   5785

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

2.       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 ……..

 

Answer:   1.07 Kohm

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

3.       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

Answer:   B

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

4.       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 ………

 

Answer:   9.4

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