Monday, December 8, 2014

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


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

Answer:    A
   Solution :           


1.       For good stabilized biasing of the transistor of the CE amplifier of the figure shown, the condition is

Answer:   B
   Solution :           


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 (Vo/Vi) is equal to __________

  Answer:   120


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

Answer:           A       


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

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

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


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 ICO 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 :


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 :

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 :

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

Answer:   3.725 mA
                Solution :

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

Answer:   3.4 Amp and 16.4 Volts

               Solution :


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 :


1.     In the cascade amplifier circuit shown, determine the values of R1, R2 and RL such that the quiescent current through the transistors is 1 mA and the collector voltages are VC1 = 3 volts, and VC2 = 6 volts. Take VBE = 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 :


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 IC is 

            a.       Indeterminate since RC is not given
            b.      1 mA
            c.       5 mA
            d.      10 mA
Answer:   B
               Solution :


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

Answer:   D
             Solution :


1.       If for a silicon NPN transistor, the base to emitter voltage (VBE) is 0.7 volts and collector to base voltage (VCB) 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 :

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

Answer:   A
                Solution :

3.   Assuming that the β of the transistor is extremely large and VBE = 0.7 volts, IC and VCE in the circuit shown are

Answer:   C
                Solution :


1.         For an NPN transistor connected as shown in figure, VBE = 0.7 volts. Given that reverse saturation current of the junction at room temperature 300oK is 10-13 amp, the emitter current is 
         a.       30 mA
         b.      39 mA
         c.       49 mA
         d.      20 mA
Answer:    C

2.       The circuit using a BJT with β = 50 and VBE = 0.7 volts is shown in figure. The base current IB and the collector voltage VC 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


Common Data for Questions (1,2 and 3):
In the transistor amplifier circuit shown in the figure below, the transistor has the following parameters: βDC = 60, VBE = 0.7 volts, hie -> , hoe -> ∞. The capacitance CC 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 βDC  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 Vo/Vs is
         a.       – 10
         b.      – 5.3
         c.       + 5.3
         d.      + 10
Answer:  A   


1.       For the BJT circuit shown, assume that the β of the transistor is very large and VBE 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 :


Statement for Linked Answer Question:
In the following transistor circuit, VBE = 0.7 volts, re = 25 mV/IE, β and all the capacitances are very large.
 1.       The value of DC current IE 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


1.     For a BJT, the common base current gain α = 0.98 and the collector base junction reverse bias saturation current, ICO = 0.6 µA. This BJT is connected in the common emitter mode and operated in the active region with a base current (IB) of 20 µA. The collector current IC 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 :


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

         a.       20
         b.      30
         c.       40
         d.      50
Answer:   C


1.       A BJT is biased in forward active mode. Assume VBE = 0.7 volts, KT/q = 25 mV and reverse saturation current IS = 10-13 Amp. The Transconductance of the BJT (in mA/volt) is…..
Answer:   5785
                  Solution :

2.       In the circuit shown, the PNP transistor has |VBE| = 0.7 volts and β = 50. Assume that RB = 100 K. For Vo to be 5 volts, the value of RC (in K) is ……..

Answer:   1.07 Kohm
               Solution :

3.       In the circuit shown, the silicon BJT has β = 50. Assume VBE = 0.7 volts and VCEsat = 0.2 volts. Which one of the following statements is correct?
         a.       For RC = 1 kΩ, the BJT operates in the saturation region
         b.      For RC = 3 kΩ, the BJT operates in the saturation region
         c.       For RC = 20 kΩ, the BJT operates in the cutoff region
         d.      For RC = 20 kΩ, the BJT operates in the linear region
Answer:   B
               Solution :

4.       For the common collector amplifier shown in the figure, the BJT has high β, negligible VCEsat and VBE = 0.7 volts. The maximum undistorted peak to peak output voltage Vo (in volts) is ………

Answer:   9.4
                 Solution :

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