Electronic Devices and Circuits Questions and Answers – Circuit Models for Amplifier

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

1. Buffer amplifier needs to have
a) Low input resistance and low output resistance
b) High Input resistance and high output resistance
c) Low input resistance and high output resistance
d) High input resistance and low output resistance
View Answer

Answer: d
Explanation: Buffer amplifiers are used to connect high input resistance source to a low output resistance load.

2. The ideal values for the input resistance (Ri) and the output resistance (Ro) of a transconductance amplifier are
a) Ri = 0 and Ro = 0
b) Ri = ∞ and R0 = ∞
c) Ri = 0 and R0 = ∞
d) Ri = ∞ and Ri = 0
View Answer

Answer: b
Explanation: It is a desired characteristics of transconductance amplifier ideally.

3. An amplifier has a voltage gain of 40db. The value of AVO is
a) 10
b) 100
c) 20
d) 200
View Answer

Answer: b
Explanation: The expression is given by 10 log AVO = 40. Solving for Avo gives 100 as the answer.
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4. The output voltage of a voltage amplifier has been found to decrease by 20% when a load resistance of 1 kΩ is connected. What is the value of the amplifier output resistance?
a) 50Ω
b) 200Ω
c) 250Ω
d) 350Ω
View Answer

Answer: c
Explanation: 250 / (1000 + 250) X 100% = 20%. Hence the output resistance is 250 ohm.

5. Which of the following is a transresistance amplifier?
a) The following is a transresistance amplifier - option a
b) The following is a transresistance amplifier - option b
c) The following is a transresistance amplifier - option c
d) The following is a transresistance amplifier - option d
View Answer

Answer: d
Explanation: Figure d is the correct representation rest are voltage, current, transconductance amplifiers.

6. The signal to be amplified is current signal and the output desired is a voltage signal. Which of the following amplifier can perform this task?
a) Voltage amplifier
b) Current amplifier
c) Transconductance amplifier
d) Transresistance amplifier
View Answer

Answer: d
Explanation: It is a characteristic of transconductance amplifier.

7. You are given two amplifiers, A and B, to connect in cascade between a 10-mV, 100-kΩ source (S) and a 100-Ω load (L). The amplifiers have voltage gain, input resistance, and output resistance as follows: for A, 100 V/V, 10 kΩ, 10 kΩ, respectively; for B, 1 V/V, 100 kΩ, 100 Ω, respectively. Your problem is to decide how the amplifiers should be connected so that the voltage gain is maximum.
a) SABL
b) SBAL
c) Both have the same voltage gain
d) None as neither combination is able to amplify the input signal
View Answer

Answer: a
Explanation: None
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8. A transconductance amplifier with Ri = 2 kΩ, Gm = 40 mA/V, and Ro = 20 kΩ is fed with a voltage source having a source resistance of 2 kΩ and is loaded with a 1-kΩ resistance. Find the voltage gain realized.
a) 18.05 V/V
b) 19.05 V/V
c) 20.05 V/V
d) 21.05V/V
View Answer

Answer: b
Explanation:
Voltage gain is 19.05 V/V for Ro = 20 kΩ is fed with voltage having resistance of 2 kΩ

9. The ratio of the short circuit current gain of a current amplifier (Ai) to the open circuit voltage gain of a voltage amplifier (AV), given that both amplifiers have the same value of the input resistance (Ri) and output resistance (R0), is
a) Ri
b) Ro
c) Ri / R0
d) Ro / Ri
View Answer

Answer: c
Explanation: It is a standard mathematical relation.
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10. The ratio of the open circuit voltage of a voltage amplifier (AV) to the short circuit transconductance of a (Gm) of a transconductance amplifier, given that both have the same value of the internal resistance (Ri) and the output resistance (R0), is
a) Ri
b) R0
c) 1/Ri
d) 1/R0
View Answer

Answer: b
Explanation: It is a standard mathematical relation.

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

To practice all areas of Electronic Devices and Circuits, here is complete set of 1000+ Multiple Choice Questions and Answers.

If you find a mistake in question / option / answer, kindly take a screenshot and email to [email protected]

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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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