Analog Electronics Test - 5 - PDF Flipbook

Analog Electronics Test - 5

290 Views
112 Downloads
PDF 4,403,693 Bytes

Download as PDF

REPORT DMCA


GATE
EEE

Analog
Electronics

Test-05Solutions


ANALOG ELECTRONICS
1. In the circuit shown below if R1 >> RP, and the impulses can

completely saturate transistor Q1, then the output voltage V0 will
be

Answer: (d)
Solution:
The given circuit is a CE amplifier circuit. The Output is 1800
out of phase from the input and due to the effect of capacitor,
the output will be distorted from the input signal.
2. In circuit shown below, capacitors C1 and C2 are very large and
are short at the input frequency. Vi is a small signal input. The
gain magnitude |V0⁄Vi| at 10 Mrad/s is

1


a) Maximum
b) Minimum
c) Unity
d) Zero
Answer: (a)
Solution:

The track circuit is resonates at a frequency

ω0 = 1 = 1
√LC √10×10−6×10−9

= 1 = 107 = 10 M rad/sec
10−14

So, Maximum gain occurs at resonant frequency or rank circuit.

2


3. Consider the following statements:
The basic purpose of bias stabilization in a transistor circuit is to
1. increase the voltage and current gain of the amplifier.
2. make the operating point of the transistor independent of
temperature variation of the transistor.
3. make the operating point independent of the replacement of
the same type, Ge or Si.
Which of the statements given above are correct?
a) 1 and 2 only
b) 2 and 3 only
c) 1 and 3 only
d) 1, 2 and 3
Answer: (b)
Solution:
Bias stabilization in a transistor is to maintain the operating
point such that the output is replica of input without any
distortion.

4. Assertion (A): The small signal analysis of a transistor
amplifier is done to obtain the current gain, voltage gain and the
conversion efficiency of an amplifier.
Reason (R): The small signal analysis of a transistor amplifier
uses the small signal parameters of the transistor.
a) Both A and R are individually true and R is the correct
explanation of A

3


b) Both A and R are individually true but R is not the correct

explanation of A

c) A is true but R is false

d) A is false but R is true

Answer: (d)

Solution:

The small signal analysis of a transistor amplifier is done to

obtain current gain, voltage gain, input impedance and output

impedance.

5. 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 drive current IB = 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:

IC = βIb + (1 + β) ICBO

β = α
1−α

IC = 1.01 mA

4


6. The product of emitter efficiency (γ) and transport factor (β*)
for a BJT is equal to
a) Small signal current gain
b) High frequency current gain
c) Power loss in the BJT
d) Large-signal current gain
Answer: (d)
Solution:
For a BJT, α = β*γ
Where α is large signal Current gain

7. The diodes Dl and D2 in the figure are ideal and the capacitors
are identical. The product RC is very large compared to the time
period of the ac voltage. Assuming that the diodes do not
breakdown in the reverse bias, the output voltage V0 (in volt) at
the steady state is _________.

Answer: 0V
Solution:

5


Diodes are ideal therefore during positive cycle if input

V0 = 10 – 10 = 0V.

During Negative cycle, the diodes are Reverse biased V0 = 0V
∴ V0 = 0 V (always)

8. Consider the following functions:

1. S2 + 3s
2(S2 + 1)

2. S4 + 3s + 1
5(S2 + 1)

3. S2 + 1
3S

4. S2 + 72S
s4 + 14s2 + 30

Which is the valid driving point impedance functions set?

a) 1, 2 and 3

b) 1, 3 and 4

c) 1, 2 and 4

d) 2, 3 and 4

Answer: (b)

Solution:

One of the conditions for driving point function to exist is that

numerator and denominator polynomial must not have missing

term between highest and lowest degrees unless all odd or even

terms are missing. Function, s4 + 3s + 1 doesn’t full fill this
5(s2 + 1)

condition and is not valid driving point impedance. 1, 3 and 4

are correct option (b).

6


9. The main drawback in the performance of shunt peaked wide
band amplifier is
a) too low gain at low frequency
b) reduced gain at middle frequency
c) poor phase response
d) that the maximum gain of the stage is small
Answer: (c)

10. Which of the following components control the high frequency
response of the R-C coupled amplifier?
1. Parasitic capacitances of the transistor
2. Coupling capacitance
3. Stray capacitances
4. Wiring capacitance
Select the correct answer using the code given below:
a) 1 and 2 only
b) 2 and 3 only
c) 3 and 4 only
d) 1, 3 and 4
Answer: (d)
Solution:
In high frequency response of the R-C coupled amplifier, the
coupling capacitance acts as a short circuit and does not play
any role.

7


11. An NPN transistor has a beta cut-off frequency fβ of 1 MHz

and Common Emitter short circuit low frequency current gain βo

of 200. The unity gain frequency fT and the alpha cut-off

frequency fα respectively are

a) 20AMHz, 201 MHz

b) 200 MHz, 199 MHz

c) 199 MHz, 200 MHz

d) 201 MHz, 200MHz

Answer: (d)

Solution:

The unity gain frequency,
(fT) = fβ × βo = 1 MHz × 200

fT = 200 MHz

fα = fβ = fβ × (β + 1) = 1⨯106 ⨯ (200 + 1) = 201 MHz
1−α 1

12. If the quality factor of a single-stage single-tuned amplifier is

doubled, the bandwidth will

a) Remain the same

b) Become half

c) Become double

d) Become four times

Answer: (b)

Solution:

Bandwidth = f0
Q

Bandwidth becomes half.

8


13. Two non-inverting amplifiers, one having a unity gain and the

other having a gain of twenty, are made using identical

operational amplifiers. As compared to the unity gain amplifier,

the amplifier with gain twenty has

a) less negative feedback

b) greater input impedance

c) greater bandwidth

d) none of the above

Answer: (a)

14. Which one of the following type of negative feedback

increases the input resistance and decreases the output resistance

of an amplifier?

a) Current series feedback

b) Voltage series feedback

c) Current shunt feedback

d) Voltage shunt feedback

Answer: (b)

Solution:

Type of Feedback Input resistance Output resistance

Current Series Decreases Decreases

Voltage Series Increases Decreases

Current Shunt Decreases Increases

Voltage Shunt increases increases

9


15. Change in the value of the Emitter resistance (RC) in a
difference Amplifier.

a) Affects the difference mode gain Ad
b) Affects the common mode gain AC
c) Affects both Ad and AC
d) Does not affect either Ad (or) AC.
Answer: (b)

Solution:

In a BJT because of Emitter -Resistor (Re) the voltage gain (AV)
decreases.

In differential Amplifier, a change in the value of the emitter

resistance (Re) affects the common mode gain AC.

i.e; Acm = −RL
2Re

16. Match List-I (Name of the oscillator) with List-II

(Characteristics) and select the correct answer using the code

given below the lists:

List-I

A. Colpitts oscillator

B. Phase shift oscillator

C. Tunnel diode oscillator

D. Relaxation oscillator

List-II

1. RC oscillator

2. LC oscillator

3. Negative resistance oscillator

10


4. Sweep circuits
Codes:

ABCD
a) 1 2 3 4
b) 2 1 3 4
c) 1 2 4 3
d) 2 1 4 3
Answer: (b)
17. Assertion (A): Op-amps with FET input stages have less gain
than those with BJT.
Reason (R): BJT has higher transconductance than FET.
a) Both A and R are true and R is the correct explanation of A
b) Both A and R are true but R is NOT the correct explanation

of A
c) A is true but R is false
d) A is false but R is true
Answer: (a)
Solution:
∴Gain ∝ transconductance. Device having low transconductance
will have low value of gain.
18. In the circuit shown in the figure, the voltage ‘v’ is given by

11


a) dvc + vc
dt

b) vc

c) dvc + RCvc
dt

d) RC dvc + vc
dt

Answer: (d)

Solution:

Current in R and C is equal,

I = CdVC = V − VC
dt R

Or, V = RC dVc + VC
dt

19. The input resistance Ri of the amplifier shown in the figure is

a) 30/4 kΩ
b) 10 kΩ
c) 40 kΩ
d) Infinite
Answer: (b)

12


Solution:

IX = VX − 0
R1

20. Consider the following circuit:

What is the function of diode D2 in the above circuit?
a) To avoid saturation of the Op-Amp
b) To provide negative feedback when the input is negative
c) To reduce reverse breakdown voltage of D1
d) As a buffer
Answer: (b)
21. A good S/H circuit should have
a) High input impedance
b) High output impedance
c) Low input impedance
d) Low output impedance

13


Answer: (d)
Solution:
Sample and hold circuit uses op-amp and an op-amp has high
input impedance and low output impedance.
22. In the ac equivalent circuit shown in the figure, if iin is the
input current and RF is very large, the type of feedback is

a) voltage - voltage feedback
b) voltage - current feedback
c) current - voltage feedback
d) current - current feedback
Answer: (b)
Solution:
The ac equivalent circuit can also be drawn in this fashion for
better understanding

14


The feedback topology is clearly shunt-shunt or current shunt
feedback or voltage sampled at output and current mixed at
input or voltage – current feedback.
23. An Op-Amp can be connected to provide
1. Voltage controlled current source
2. Current controlled voltage source
3. Current controlled current source
Which of the above statements are correct?
a) 1 and 2 only
b) 1 and 3 only
c) 2 and 3 only
d) 1, 2 and 3
Answer: (a)
24. Which one of the following statements is not correct in respect
of a series transistor feedback voltage regulator?
a) The regulation factor can be improved by increasing the ℎ

of the shunt transistor
b) The regulation factor can be improved by increasing the

resistance between the collector of the shunt transistor and
the collector of the series transistor
c) Output resistance can be reduced by using a Darlington pair
in place of the series transistor
d) Output resistance can be reduced by reducing the hfe of the
shunt transistor
Answer: (d)

15


25. Consider the following statements regarding the class B power
amplifiers (Complementary symmetry type):
1. The efficiency of the amplifier is higher than that of class-A
amplifier.
2. The power output is low.
3. Crossover distortion is present.
4. The standby power dissipation is absent.
Which of the above statements are correct?
a) 1, 2 and 3
b) 1, 2 and 4
c) 1, 3 and 4
d) 2, 3 and 4
Answer: (c)
Solution:
i. In Class-B power amplifiers (complementary symmetry type),
one transistor is ON for the half cycle and other transistor is
ON for the remaining half cycle. Therefore, standby power
dissipation is absent.

ii. Maximum possible conversion efficiency of Class-B amplifier
is 78.5% as compared with 50% for class-A amplifier.

iii. The output of power amplifiers is high.
iv. At very low signal levels, class-B operation introduces severe

distortion called crossover distortion due to cut in voltage of a
transistor and the non-linearity in the low signal area.

16


26. Consider the following statements regarding linear power
supply:
1. It requires low frequency transformer.
2. It requires high frequency transformer.
3. The transistor works in active region.
Which of the above statement(s) is/are correct?
a) 1 only
b) 2and 3only
c) 1 and 3 only
d) 3 only
Answer: (c)
Solution:
In linear power supply we required low frequency transformer
because the power transmission occur at low frequencies and the
transistor works in active region.

27. Which one of the following circuits is used for converting a
sine wave into a square wave?
a) A stable multivibration
b) Monostable multivibration
c) Bistable multivibration
d) Schmitt trigger
Answer: (d)
Solution:
Schmitt trigger converts an irregular shaped waveform to a
square wave.

17


28. A cascade Amplifier stage is equivalent to
a) A common emitter stage followed by a common base stage.
b) A common base stage followed by an Emitter follower.
c) An Emitter follower stage followed by a common base stage.
d) A common base stage followed by a common Emitter stage.
Answer: (a)

29. The gain of an amplifier will be more affected by change in
transistor parameter in case of
a) positive feedback
b) negative feedback
c) zero feedback
d) none of these
Answer: (a)

30. In an intrinsic semiconductor.
a) with increasing temperature, the density of electron hole pairs
increases
b) in intrinsic germanium the resistivity increases 6% per degree
rise in temperature
c) at low temperature, will above 0K, electrons move into the
valence band
d) holes along with electrons carry current in the conduction
band
Answer: (a)

18


Data Loading...