Analog Electronics Test - 4 - PDF Flipbook
Analog Electronics Test - 4
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Analog
Electronics
Test-04Solutions
ANALOG ELECTRONICS
1. Assertion (A): In the circuit shown in the figure, a prescribed
value of load current IL, V0 will gradually fall.
Reason (R): Above the prescribed value, as load current IL
increases, IB decreases.
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: (c)
2. When used for amplification, the output port side of a BJT
behaves as a controlled current source. According to the above,
the variation of which one of the following does not change the
output current of an ideal BJT? (The BJT is being used in a
common emitter amplifier circuit)
a) Load resistance
b) Collector to the base bias voltage
c) Both load resistance and collector to a base bias voltage
d) Base-emitter bias voltage
1
Answer: (c)
Solution:
Approximate h-parameter modal of BJT.
VBE changes IB which in turn changes βib.
3. For an npn transistor connected as shown in the figure, VBE =
0.7 volts. Given that reverse saturation current of the junction at
room temperature 300o K is 10 –13, the emitter current is (η = l)
a) 30 mA
b) 39 mA
c) 49 mA
d) 20 mA
Answer: (c)
Solution:
When two Terminals of a Transistor are shorted then it acts as a
Normal Diode.
Then Diode Current Equation is
2
I = Io �eηVVPT − 1�
For Ge, η = 1, I0 = 10 – 13 given
VT = 26 ⨯ 10 – 3
0.7
I = 10 – 13 �e1 × 26 × 10−3 − 1�
I = 49 mA
4. In the circuit shown, assume that the diodes D1 and D2 are ideal.
The average value of voltage Vab (in Volts), across terminals ‘a’
and ‘b’ is _____.
Answer: 5
Solution:
During POS cycle D1 is FB, D2 is RB
Vab = Vin = 6π sin ωt = 2πsinωt
3 3
During negative cycle D1 is RB
During negative Cycle D2 is FB
3
Vab = Vin = 6π sin ωt = 3πsinωt
2 2
Vab(avg) = 2π + 3π = 5 (volt)
π π
5. Which of the following describe the correct properties of an
emitter follower circuit?
1. It is a voltage series feedback circuit
2. It is a current series feedback circuit.
3. Its voltage gain is less than unity
4. Its output impedance is very low.
Select the correct answer from the codes given below:
a) 1, 3 and 4
b) 2,3 and 4
c) 2 and 3 only
d) 2 and 4 only
Answer: (a)
4
6. Consider the following statements:
A Schottky diode is included when a transistor is fabricated so
as to
1. Prevent the transistor from full saturation.
2. Eliminate saturation delay time.
3. Achieve better switching speed.
4. Reduce thermal stability.
Which of the above statements are correct?
a) 1, 2 and 4 only
b) 1, 2 and 3 only
c) 2, 3 and 4 only
d) 1, 2 3 and 4
Answer: (b)
Solution:
Consider the figure shown above because of the drop against the
Schottky diode the emitter base junction will never enter into
saturation region. Thus, by eliminating the saturation delay time
now the transistor will never enter into the saturation region.
Addition of Schottky diode also reduces the reverse recovery
time of the diode hence increasing the switching speed.
5
7. The circuit of fig. uses an ideal Op-Amp for small positive
values of Vin, the circuit works as
a) a half wave rectifier
b) a differentiator
c) a logarithmic amplifier
d) an exponential Amplifier
Answer: (c)
8. Consider the constant current source shown in the figure below.
Let B represent the current gain of the Transistor
The load current I0 through RL is
a) I0 = �β + 1� Vref
β R
b) I0 = �β β 1� Vref
+ R
c) I0 = �β + 1� Vref
β 2R
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d) I0 = �β β 1� Vref
+ 2R
Answer: (b)
Solution:
VP = VN [Virtual short]
Io= Ic = �β β 1�IE
+
= �β β 1� VZ
+ R
9. Consider the following statements: The lower cut-off
frequencies for an RC coupled CE amplifier depend on
1. input and output coupling capacitors
2. emitter bypass capacitor
3. junction capacitors
Which of these statements is/are correct?
a) 1 alone
b) 2 alone
c) 1 and 2
d) 2 and 3
Answer: (c)
7
Solution:
For the RC-Coupled amplifier, the drop at low frequencies is
due to the increasing reactance of CC, CE, or CS while its upper
frequency limit is determined by either the parasitic capacitive
elements of the network and frequency dependence of the gain
of the active device.
10. Consider the following statements:
We would be able to achieve broad banding in a common source
FET amplifier, by
1. resonance between the shunt capacitance and a
compensating inductance.
2. RC compensating network between source and drain.
3. connecting compensating network in series with the coupling
capacitors.
Which of the statements given above is/are correct?
a) Only 1
b) 1 and 2
c) 1 and 3
d) 2 and 3
Answer: (a)
11. Consider the following statements pertaining to frequency
response of RC coupled amplifier:
1. Coupling capacitance affects high frequency response.
2. Bypass capacitance affects high frequency response.
3. Coupling capacitance affects low frequency response.
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4. Bypass capacitance affects low frequency response.
Which of the above statements are correct?
a) 1 and 2
b) 3 and 4
c) 2 and 3
d) 1 and 4
Answer: (b)
Solution:
In an R-C amplifier
1. The Low Frequency response is governed by Transistor
coupling capacitance.
2. High frequency response is governed by transistor junction
capacitance.
3. Gain Bandwidth product remains constant.
4. The miller capacitance reduces the gain at high frequency.
Hence Option (b) is Correct.
12. Match the following
Group - I
A. Hartley
B. Wein-bridge
C. Crystal
Group - II
1. low frequency oscillator
2. High frequency oscillator
3. Stable frequency oscillator
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4. Relaxation oscillator
5. Negative Resistance oscillator
a) A – 2, B – 1, C – 3
b) A – 1, B – 2, C – 3
c) A – 3, B – 1, C – 2
d) A – 1, B – 3, C – 1
Answer: (a)
Solution:
Hartley oscillators works in the high frequency like RF range.
Wein-bridge oscillator work in the low frequency like AF range.
Crystal oscillators works in stable frequency oscillators.
13. In a bipolar transistor at room temperature, if the emitter
current is doubled the voltage across its base-emitter junction
a) doubles
b) halves
c) increase by about 20 mV
d) Decrease by about 20 mV
Answer: (c)
Solution:
=IE2 IES�eVBE2⁄VT−1−1�
IE1 IES�eVBE1⁄VT−1−1�
∴ IE2 = 2 IE1
⇒ 2IE1 = eVBE2⁄VT = e(VBE2−VBE1)⁄VT
IE1 eVBE1⁄VT
⇒ VBE2 − VBE1 = VT ln(2) = 18 mV
∴ Δ VBE = 18 mV
10
14. Match List-I (Type of Feedback) with List-II (Effect on Rin
and Rout) and select the correct answer using the code given
below the lists
List-I
A. Voltage series
B. Voltage Shunt
C. Current Series
D. Current shunt
List-II
1. Rin increases and Rout decreases
2. Rin and Rout decrease
3. Rin and Rout increase
4. Rin decreases and Rout increases
Codes:
ABCD
a) 1 4 3 2
b) 3 2 1 4
c) 3 4 1 2
d) 1 2 3 4
Answer: (d)
Solution:
Note 1: For Series Comparison, Rin increases whereas for shunt
mixing Rin decreases.
Note 2: For voltage Sampling, Rout decreases whereas for
current sampling, Rout increases.
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15. An amplifier will generate stable sinusoidal oscillations if we
provide feedback such that
a) its poles lie close to jω-axis in the right half of s-plane
b) its poles lie close to jω-axis in the left half of s-plane
c) its poles lie on the +ve real axis in s-plane
d) its poles lie anywhere in s-plane
Answer: (a)
Solution:
16. Assertion (A): Inductors carrying steady direct currents act as
effective short circuits with zero voltage across it.
Reason (R): The voltage induced across an inductance is
proportional to the rate of change of current di/dt.
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 a correct explanation of
A.
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c) A is true, but R is false.
d) A is false, but R is true
Answer: (a)
Solution:
VL ∝ ddti; VL = L di
dt
For d.c. di = 0 ⇒ V= 0
dt
Inductor acts as Short-circuit.
17. The amplifier circuit shown below uses a silicon transistor. The
capacitors Cc and CE can be assumed to be short at signal
frequency and the effect of output resistance r0 can be ignored. If
CE is disconnected from the circuit, which one of the following
statements is TRUE?
a) The input resistance Ri increases and the magnitude of
voltage gain AV decreases
b) The input resistance Ri decreases and the magnitude of
voltage gain AV increases
13
c) Both input resistance Ri and the magnitude of voltage gain AV
decrease
d) Both input resistance Ri and the magnitude of voltage gain
AV increase
Answer: (a)
Solution:
If CE is disconnected, then by RE, the overall voltage gain is
decreased. But the input resistance increases.
18. Consider the following statements related to oscillator circuits
1. The tank circuit of a Hartley oscillator is made up of a tapped
capacitor and a common inductor.
2. The tank circuit of a Colpitts oscillator is made up of a tapped
capacitor and a common oscillator.
3. The Wien Bridge oscillator is essentially a two-stage
amplifier with an RC bridge in the first stage, and, the second
stage serving as an inverter.
4. Crystal oscillators are fixed frequency oscillators with a high
Q-factor.
Which of the above statements are correct?
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a) 1, 2 and 3 only
b) 2,3 and 4 only
c) 1,2 and 4 only
d) 1, 3 and 4 only
Answer: (b)
Solution:
• A Colpitts oscillator is made up of a tapped capacitor in the
tank circuit and a common oscillator.
• The Wein Bridge oscillator is essentially a two-stage
amplifier with an RC bridge in the first stage, and the second
stage serving as an inverter.
• Crystal oscillators are fixed frequency oscillators with a high
Q-factor.
19. A triangular-square wave generator uses
a) A sine wave oscillation and a comparator
b) An integrator and a comparator
c) A differentiator and a comparator
d) A sine wave oscillator and a clipper
Answer: (b)
20. 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 l0% tilt is ______ Hz.
Answer: 1.59
15
Solution:
Fractional tilt = π.fL
f
∴ fL = f × tilt = 50 × 10 = 1.59 Hz
π π 100
21. Which of the following are the non-linear applications of Op-
Amp?
1. Current-to-voltage converter
2. Comparator
3. Peak detector
4. Limiter
Select the correct answer from the codes given below:
a) 1, 2 and 3
b) 2, 3 and 4
c) 1, 3 and 4
d) 1, 2 and 4
Answer: (b)
Solution:
Current-to-voltage converter is a linear application of op-amp.
Some non-linear applications are:
• Comparator
• Peak detector
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• Limiter
• Log amplifier
• Rectifier
22. Match List-I (Application of the Circuit) with List-II
(Circuit Name) and select the correct answer using the codes
given below the lists:
List-I
A. Divider
B. Clips input voltage at two predetermined levels
C. Square wave generator
D. Narrow current pulse generator
List-II
1. A stable multivibrator
2. Schmitt trigger
3. Bistable multivibrator
4. Blocking oscillator
Codes:
ABCD
a) 4 2 1 3
b) 3 2 1 4
c) 4 1 2 3
d) 3 1 2 4
Answer: (b)
17
23. The circuit shown in the figure is that of
a) a non-inverting Amplifiers
b) an inverting Amplifier
c) an oscillator
d) a Schmitt triggers
Answer: (d)
24. The large signal bandwidth of an operational amplifier is
limited by its
a) CMRR
b) Slew rate
c) Gain-bandwidth Product
d) Input impedance
Answer: (b)
Solution:
The D.C and the large signal operation is limited by the slew
rate of the op-amp.
25. Which one of the following power amplifiers has the
maximum efficiency?
a) Class A
b) Class B
c) Class AB
d) Class C
Answer: (d)
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Solution:
Increasing order of efficiency: Class A < Class AB < Class B
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