Define negative feedback in a closed - loop control system?

I will try to explain using examples. calculations attached respectively:- A system has a gain of 80 dB without feedback. If the negative feedback fraction is 1/50th. Calculate the closed-loop gain of the system in dB with the addition of negative feedback. Negative feedback example:- Then we can see that the system has a loop gain of 10,000 and a closed-loop gain of 34 dB. Negative Feedback Example No 2:- If after 5 years the loop gain of the system without negative feedback has fallen to 60 dB and the feedback fraction has remained constant at 1/50th. Calculate the new closed-loop gain value of the system. Negative feedback example 3: Then we can see from the two examples that without feedback, after 5 years of use the systems gain has fallen from 80 dB down to 60 dB, (10,000 to 1,000) a drop in open loop gain of about 25%. However with the addition of negative feedback the systems gain has only fallen from 34 dB to 33.5 dB, a reduction of less than 1.5%, which proves that negative feedback gives added stability to a systems gain. Therefore we can see that by applying negative feedback to a system greatly reduces its overall gain compared to its gain without feedback. The systems gain without feedback can be very large but not precise as it may change from one system device to the next, then it is possible to design a system with sufficient open-loop gain that, after the negative feedback has been added, the overall gain matches the desired value. Also, if the feedback network is constructed from passive elements having stable characteristics, the overall gain becomes very steady and unaffected by variation in the systems inherent open-loop gain. read less

Negative feedback is accomplished by adding part of the output signal out of phase with the input signal. You have seen that an emitter resistor in a common-emitter transistor amplifier will develop a negative feedback signal. Other methods of providing negative feedback are similar to those methods used to provide positive feedback. The phase relationship of the feedback signal and the input signal is the only difference. read less