ECE

ELECTRONIC CIRCUITS PART-2

21. What is an amplifier?
An amplifier is a device which produces a large electrical output of similar characteristics to that of the input parameters.

22. How are amplifiers classified according to the input?
1. Small – signal amplifier 
2. Large – signal amplifier

23. How are amplifiers classified according to the transistor configuration?
1. Common emitter amplifier
2. Common base amplifier 
3. Common collector amplifier

24. What is the different analysis available to analyze a transistor?
1. AC analysis 
2. DC analysis

25. How can a DC equivalent circuit of an amplifier be obtained?
By open circuiting the capacitor.

26. How can a AC equivalent circuit of a amplifier be obtained?
By replacing dc supply by a ground and short- circuiting capacitors.

27. What is feed back?
It is the process of injecting some energy from the output and then returns it back to the input.

28. What are feed back amplifiers?
Amplifiers which uses feed back principle is called as feed back amplifiers.

29. What are the types of feed back?
1. Positive feedback 
2. Negative feedback.

30. What is positive feedback?
If the feed back signal is applied in such a way that it is in phase with the input signal and thus increases it is said to be positive feedback.

31. What is negative feed back?
If the feed back signal is applied in such a way that it is out of phase with the input signal and thus decreases it is said to be positive feedback.

32. Which feedback decreases the gain of the amplifier?
Negative feed back

33. Which feedback increases the gain of the amplifier?
Positive feedback

34. What is the advantage of negative feed back?
1. increased stability 
2. Increased bandwidth
3. Decreased noise 
4. Less frequency distortion

35. What is the disadvantage of negative feed back?
Reduces amplifier gain. 

36. Define sensitivity.
It is the ratio of percentage change in voltage gain with feedback to the percentage change in voltage gain without feed back. 

37. Define Desensitivity.
It is the ratio of percentage change in voltage gain without feedback to the percentage change in voltage gain with feed back. the reciprocal of sensitivity.

38. What is an op-amp?
The operational amplifier is a multi-terminal device, which is quite complex internally. An operational amplifier is a direct coupled high gain amplifier usually consisting of one or more differential amplifiers and usually
followed by a level translator and an output stage. An operational amplifier is available as a single integrated circuit package. It is a versatile device that can be used to amplify dc as well as ac input signals and was originally designed for computing such mathematical functions.

39. What are the characteristics of ideal op-amp?
a. Open loop voltage gain, (AOL) = ’infinity
b. Input impedance (Ri) = ’’infinity
c. Output impedance (Ro) = 0
d. Bandwidth (BW) = ’’infinity
e. Zero offset Vo = 0, when V1 = V2 = 0

40. Define loading?
A large value of Rc cannot be used in a circuit since,a large value of resistance requires a large chip area.
For large Rc, quiescent drop across it increases and hence a large power supply is required.
These difficulties removed by using a current source. Hence, a current source can also be used as an active load for an amplifier to obtain a very large voltage gain

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