Viva question and answer about amplifier

some viva question and answer about  amplifier

1. What is the main difference between general amplifier and power amplifier?

General amplifier can amplify voltage or current or both, but output power. power amplifier can increase the output power.

2. Why can't we get more current and voltage gains using general amplifier?

In general amplifier voltage gain is more but current gain is less because as current increases heat dissipation increases across transistor increases so transistor will be burned.

3. Is the power amplifier amplifies the power of input signal?

yes.

4. What are the classifications of Power amplifiers?

Basically 2 types: Audio power amp and Radio power amplifier.
Based on mode of operation: Class A, Class B, Class AB, Class C, Class D.

5. Which power amplifier has more efficiency?
Class D6. Define efficiency?
It is defined as ratio of output power and input power.

7. What are the efficiencies of various power amplifiers?
Class A = 50%
Class B = 78.5%  
Class C = 90%
Class D = 100%

8. Define cross over distortion, and how it can be overcome?
Due to the switching times of transistor a flat top occurs in output of Class B power amplifier. To avoid it the two transistors will normally be biased at a level that is slightly above cut-off.

9. What are the percentage of active region in various Power amplifiers?
Class A = 100%
Class B = 50%
Class AB = 50-100%  
Class C = less than 50%

10. What is total harmonic distortion?

It is the ratio of the sum powers of all harmonic components to power of the fundamental frequency. 

11.Define power dissipation in power amplifiers?

It is defined as product of collector current and voltage across collector and emitter. 

12. Specify Q-point location on load line for different power amplifiers?

Class A - Middle point DC load line
Class B - on Vce axis on load line
Class AB - nearer to Vce axis on load line  
Class C - down side of Vce axis on load line.

13. Where we can use Class A power amplifier?

Low power amplifiers where efficiency is not important

14. Where we can use Class B power amplifier?

Output power amplifiers.

15. Where we can use Class C power amplifier?

Tuned RF amplifiers but can not used as audio amplifiers due to high distortion.

16.What do you mean by a precision diode?

The major limitation of ordinary diode is that it cannot rectify voltages below the cut in voltage of the diode the precision diode is capable of rectifying input signals of the orderof millivolt.

17.What are the applications of precision diode.

· Half waveRectifier
· Full Wave rectifier
· Peak value detector
· Clipper, Clamper

18.What are the applications of Log amplifier?

Multiplier, divider.

19.What are the limitations of the basic differentiator circuit?

At high frequency, a differentiator may become unstable and break into oscillations, The input impedance decreases with increase in frequency.

20.What are the limitations of the basic Integrator circuit?

At low frequency, a integrator may become unstable and break into oscillations, The input impedance decreases with decrees in frequency.

21. What Are The Applications Of Integrator?

Integrators are widely used in ramp or sweep generators, filters, analog computers etc.

22. Why op-amp Is Used Mostly As An Integrator Than A Differentiation?

Op-amp is used mostly as an integrator than a differentiator because in differentiator at high frequency, gain is high and so high-frequency noise is also amplified which absolutely abstract the differentiated signal.

23. Explain What Do You Mean By Operating Point?

The zero signal values of IC and VCE are known as the operating point. It is called operating point because the variations of IC and VCE take place about this point when signal is applied. It is also known as the quiescent or Q-point.

24. Explain What Is Transistor Biasing?

The proper flow of zero signal collector current and the maintenance of proper collector emitter voltage during the passage of signal is called the transistor biasing.

25. Explain What Is Faithful Amplification?
The process of raising the strength of a weak signal without any change in its general shape is referred to as faithful amplification.

26. Explain What Is The Effect Of Removal Of Bypass Capacitor In A Ce Amplifier Circuit?

Removal of bypass capacitor in a CE amplifier circuit causes excessive degeneration in the amplifier circuit and therefore reduction in voltage gain.

27. Mention The Two Applications of tuned amplifiers.

i) They are used in IF amplifiers in Radio and TV receivers.
ii) They are used in wireless communication systems.

28. State two advantages and two disadvantages of tuned amplifiers.
Advantages:

i) They amplify defined frequencies
ii) Signal to noise ratio (SNR) at output is good.

iii) They are suited for radio transmitters and receivers.
Disadvantages:
i) They are not suitable to amplify audio frequencies.
ii) Circuit is bulky and costly.
iii) The design is complex.

 29. What is neutralization in tuned amplifiers?
The effect of collector to base capacitance of the transistor is neutralized by introducing a signal that cancels the signal coupled through collector base capacitance. This process is called neutralization .

30. What is narrow band neutralization?
A process of cancelling the instability effect due to the collector to base capacitance of the transistor in tuned circuits by introducing a signal which cancels the signal coupled through the collector to base capacitance is called narrow band neutralization.