Distortion with Feedback

Distortion with Feedback

AU ; May-03,10,13, Dec.-10

1. Frequency Distortion

• From equation A_f = 1 / β we can say that if the feedback network does not contain reactive elements, the overall gain is not a function of frequency. Under such conditions frequency and phase distortion is substantially reduced by negative feedback.

• If β is made up of reactive components, the reactances of these components will change with frequency, changing the p. As a result, gain will also change with frequency. This fact is used in tuned amplifiers.

• In tuned amplifiers, feedback network is designed such that at tuned frequency β → 0 and at other frequencies β → ∞ . As a result, amplifier provides high gain for signal at tuned frequency and relatively reject all other frequencies.

2. Noise and Nonlinear Distortion

• Signal feedback reduces the amount of noise signal and non linear distortion. The factor (1+ PA) reduces both input noise and resulting nonlinear distortion for considerable improvement. Thus, noise and non linear distortion also reduced by same factor as the gain.

Review Questions

1. What are the effects of negative feedback on distortion of an amplifier ?

2. Explain how negative feedback acts on a distortion.

3. What is the effect of negative feedback on distortion, of a feedback amplifier ?

AU : ECE : Dec.-10, May-13, Marks 6

4. What is frequency distortion ?

5. What is the effect of negative feedback on noise and nonlinear distortion ?

AU : Dec.-09, 12, 16, May-05, 06, 07, 09, 17