Electronic Devices and Circuits Questions and Answers – Multistage Amplifier

This set of Electronic Devices and Circuits Multiple Choice Questions & Answers (MCQs) focuses on “Multistage Amplifier”.

1. The frequency response of transformer coupling is ________
a) Good
b) Very Good
c) Excellent
d) Poor
View Answer

Answer: d
Explanation: The transformer coupling has a poor frequency response. The gain varies considerably with frequency. The gain is constant only over small range of frequencies. Thus transformer coupling introduces frequency distortion; due to which its frequency response is poor.

2. What is the purpose of RC or transformer coupling?
a) To block a.c.
b) To separate bias of one stage from another
c) Increase thermal stability
d) Increase Efficiency
View Answer

Answer: b
Explanation: In RC or transformer coupling, a capacitor / transformer is used as coupling device which connects output of first stage with input of second stage. Its function is to pass the a.c signal and blocks d.c. bias voltage.

3. Why is RC coupling confined to low power applications?
a) Due to large value of coupling capacitor
b) Low efficiency
c) Large number of components
d) Due to is frequency response
View Answer

Answer: b
Explanation: RC coupled amplifiers have low voltage and power gain. It is because the low resistance presented by the input of each stage to the preceding stage decreases the effective load resistance and hence the gain. Thus its efficiency is reduced.

4. A radio receiver has how many stages of amplification?
a) One
b) Two
c) Three
d) More than one
View Answer

Answer: d
Explanation: A multistage amplifier circuit affects the high input impedance of a common source stage combined with the input to output isolation of a common gate stage. A radio receiver has more than one stage of amplification because it is required to restore the characteristics of a radio signal over various channels.

5. Which of the following is an advantage of RC coupling scheme?
a) Good impedance matching
b) Economy
c) High efficiency
d) Frequency response
View Answer

Answer: b
Explanation: It uses the resistor and capacitor which are not expensive so the cost is low. But it has poor impedance matching because its output impedance is several times larger than the device; at its terminal end. It is unsuitable for low frequency application.
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6. The voltage gain is practically expressed in _______
a) db
b) volts
c) as a number
d) ampere
View Answer

Answer: a
Explanation: Db scale is logarithmic. Voltage gain increases exponentially with frequency so using a linear scale means that we need to work with large values of gain, corresponding to small values of frequency.

7. If a three stage amplifier has individual stage gains of 10db, 6db and 15db; then the total gain in db is ______
a) 600db
b) 24db
c) 14db
d) 31db
View Answer

Answer: d
Explanation: The overall gain of a multistage amplifier is given as the product of the gain of the individual stages.
Gain (A) = A1 * A2 * A3 ……* An
Alternately, if the gain of each stage is given in db
The overall gain of the amplifier is the sum of gain of each stage
Gain in db = A1 + A2 + A3 (db)
= 10+6+15 = 31db.

8. For extremely low frequencies, RC coupling is not used because of ___________
a) There is considerable power loss
b) There is a hum in the output
c) Electrical size of the coupling capacitor
d) Low efficiency
View Answer

Answer: c
Explanation: Xc = the electrical size of coupling capacitor
Relation of Xc with the signal frequency (f):
Xc = 1 \Xc is inversely proportional to f.
At low frequencies, Xc becomes very large; output reactance of capacitor increases.
The voltage across load resistance also reduces because some voltage drop takes place across Xc.
Thus output voltage reduces. Therefore gain is very low.

9. Which transformer is used for impedance matching in transistor coupled amplifier?
a) step-up
b) step-down
c) same turn ratio
d) different turn ratio
View Answer

Answer: b
Explanation: Usually the impedance of an output device is a few ohms whereas output impedance of the transistor is several 100 ohms. In order to match the impedance a step down transformer of proper turn’s ratio is used. The impedance of secondary of the transformer is made equal to the load impedance and primary impedance equal to the output impedance of the transistor.

10. Gain of an amplifier usually expressed in db because _______________
a) It is a small unit
b) Calculations become easy
c) Human ear response is logarithmic
d) Gain is reduced
View Answer

Answer: c
Explanation: The human hearing scale is logarithmic in nature. For doubling perceived intensity of sound, the sound power must be increased by 10 times. That means the gain of amplifier which controls sound intensity must have gain of 10 for doubling perceived intensity of sound which is in a bell and in 10 decibel scale.

11. The total gain of a multistage amplifier is less than the product of the gains of individual stages due to ___________
a) Power loss in the coupling device
b) Loading effect of the next stage
c) The use of many transistors
d) The use of many capacitors
View Answer

Answer: b
Explanation: The output of first amplifier stage is the input to next stage. In this way overall voltage gain can be increased, when number of amplifier stage is used in succession, it is called a multistage amplifier. The load of first amplifier is the input resistance of the second amplifier. Thus overall gain is reduced.

Sanfoundry Global Education & Learning Series – Electronic Devices and Circuits.

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Manish Bhojasia, a technology veteran with 20+ years @ Cisco & Wipro, is Founder and CTO at Sanfoundry. He lives in Bangalore, and focuses on development of Linux Kernel, SAN Technologies, Advanced C, Data Structures & Alogrithms. Stay connected with him at LinkedIn.

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