The negative feedback improves all performance parameters of an amplifier except its : 

Effects of negative feedback:

• Reduces the parameter variation by a factor 1 + GH.
• Reduces the effect of noise and disturbance on the system performance.
• Bandwidth increases by the factor of 1 + GH.
• The system becomes more accurate.
• Improves the sensitivity of the system, a good system should less sensitive to parameter variations but sensitive to the input command.

Important Points

1. Feedback affects the gain G of a non-feedback system by a factor of 1 ± GH.
2. Generally, feedback may increase or decrease the gain. In practical control cases, G and H are functions of frequency.
3. So, the magnitude of 1 ± GH may be greater than '1' for some range of frequency and it is less than '1' in another range of frequency.
4. Therefore, feedback could increase the gain of the system in one frequency range but decrease it in another.

Effect of feedback on stability:

• The closed-loop system depends on loop gain. If the loop gain GH = - 1 for a negative feedback system, the output of a system becomes infinity for the finite input and the system is said to be unstable.
• Hence, the feedback can improve stability or can be harmful to stability if it is not properly applied.

Important Points

The magnitude of the sensitivity of the system with respect to the feedback path parameter (H) is usually more than the magnitude of the sensitivity of the system with respect to the forward path parameter (G).

⇒ |SHT| > |SGT|