Important Two Marks Questions with Answers on Amplifiers

TWO MARKS QUESTION AND ANSWERS

1. Define an Amplifier.

An amplifier is defined as the device which increases the magnitude of the input signal and produces a larger electrical output.

2. What do you mean by linear amplifier?

If the output signal is directly proportional to the corresponding input signal, then the amplifier is called linear amplifier.

3. What is meant by non-linear amplifier?

If the output signal is not directly proportional to the input signal, then the amplifier is called non-linear amplifier.

4. How amplifiers are classified based on configuration?

i. Common Emitter (CE) amplifier

ii. Common Base (CB) amplifier

iii. Common Collector (CC) amplifier

5. Draw the transistor two port model.

6. Define small signal amplifier.

The amplifier which operates on small signal is called small signal amplifier small signal indicates that the input signal is very small in the range of few mV.

7. What do you mean by hybrid parameter?

The input current i₁ and the output voltage V₂ are taken as independent variables. The input voltage V₁ and the output current i₂ are expressed in terms of i₁ and V₂. The units of these four parameters are completely different from each other, these parameters are called hybrid parameters.

8. What are the factors affecting h-parameters?

i. Transistor type

ii. Transistor configuration

iii. Operating point

iv. Frequency

v. Temperature

9. What are the advantages of h-parameter?

i. Easy to measure from static characteristics of transistor

ii. Simple conversion from one configuration to other

iii. Can be used upto radio frequencies.

iv. Convenient for circuit analysis and design.

10. List the steps involved in small signal analysis of amplifier.

i. Draw the ac equivalent circuit of the amplifier

ii. Draw the hybrid equivalent circuit

iii. Calculate the input impedance, output impedance, current gain and voltage gain.

11. How ac equivalent circuit is obtained?

i. Replace the dc voltage source by short circuit

ii. Replace coupling and bypass capacitor by short circuit.

12. Write the characteristics of CE amplifier.

i. Good voltage gain

ii. Output voltage is 180° out of phase with input

iii. Good current gain and power gain

13. List the characteristics of CB amplifier.

i. Provides voltage gain and power gain

ii. High output impedance and very low input impedance

iii. No current gain

14. List the characteristics of CC amplifier.

i. Provides current gain and power gain

ii. High input impedance and very low output impedance 3. No voltage gain

15. Why common drain amplifier is called source follower?

The input signal is applied to the gate terminal and the output terminal is taken from the source terminal. The source exactly follows the input signal. Hence it is called as source follower.

16. Write the properties of common source amplifier.

i. High input and output impedance

ii. Relatively high small-signal voltage gain.

iii. Very high small-signal current gain.

17. List the properties of common drain amplifier.

i. Non inverting amplifier

ii. Very large input impedance

iii. Small output impedance

iv. Voltage gain AV < 1

v. Large small-signal current gain

18. What is the need for multistage amplifier?

i. When input or output impedance is not of correct magnitude for the intended application.

ii. When amplification of simple stage amplifier is not sufficient.

19. Define voltage gain of the cascaded amplifier.

The voltage gain of the cascaded amplifier is defined as the product of the individual voltage gain of each stage.

20. How voltage gain is expressed in terms of current gain?    

21. What are the high frequency effects?

When the frequency is increased sufficiently, the internal capacitances start becoming significant and start affecting the voltage gain. The coupling and bypass capacitors offer a very low reactance and hence they can be treated as short circuits.

22. What are the causes for upper cut-off frequencies in BJT.

Main causes for upper cut-off frequencies in BJT are that the amplifier gain reduces at low and high frequencies. A range of frequencies over which the voltage gain, is close to or equal to A_V is obtained.

23. Compare the gain at low frequency and high frequency region.

The amplifier gain in low frequency region decreases due to coupling and bypass capacitors.

In high frequency region, the output voltage and gain will decrease due to transistor internal capacitance and stray capacitance.

 

REVIEW QUESTIONS

1. Discuss the effect of coupling capacitor and bypass capacitor on low frequency response of BJT amplifiers.

2. Draw the high frequency equivalent circuit of a transistor and explain.

3. Derive the expression for 3-dB cut-off frequency of emitter follower using its equivalent circuit.

4. Explain in detail the operation of CE amplifier and its high frequency equivalent circuit.

5. Why is CC amplifier called source follower? Explain.

6. Draw the equivalent circuit of common-source amplifier at high frequencies and derive expressions for voltage gain, input and output impedance.

7. What are the parameters that will influence the frequency response of FET amplifiers? Explain.

8. Draw the high frequency model of FET.

9. How are amplifiers classified? Explain.

10. What do you mean by hybrid parameters? Explain.

11. Explain the steps involved in small signal analysis of transistors..

12. Explain the analysis of CE amplifier with emitter resistor.

13. Explain in detail the construction operation and analysis of CB amplifier.

14. Draw the hybrid equivalent circuit of common drain amplifier and derive its parameters.

15. Explain in detail the small signal analysis of common gate JFET amplifier.

16. Discuss the steps involved in small signal analysis of MOSFET.

17. Derive the input impedance, output impedance, voltage gain and current gain of common source MOSFET amplifier.

18. Explain the operation of common drain MOSFET amplifier and derive its parameters.

19. Explain the gain and frequency response of BJT amplifier.

20. Discuss the frequency response of FET amplifier.

21. List the need for multistage amplifier. Derive its voltage gain.