Negative feedback and linearity

[shilpashetty]

hello

I read that negative feedback, but I can see it intuitively

Can you give me an intuitive explanation of this phenomenon

Thank you

 

[ckshivaram]

Negative feedback occurs when the output of a system acts to oppose changes to the input of the system, with the result that the changes are attenuated. If the overall feedback of the system is negative, then the system will tend to be stable.


see if it helps
http://www.pcc.lth.se/events/workshops/2001/pccposters/Lantz.pdf
**broken link removed**

 

[shilpashetty]

thank you ckshivaram
actually i missed a part of my question
that was about the effect of Negative feedback on linearity

hello

I read that negative feedback improves linearity, but I can see it intuitively

Can you give me an intuitive explanation of this phenomenon

Thank you

 

[LvW]

thank you ckshivaram
actually i missed a part of my question
that was about the effect of Negative feedback on linearity

Hi Shilpashetty, the most simple explanation is as follows:
For negative feedback the gain increasingly depends on the feedback network. That means, the transfer characteristics of the feedback elements (resistors) dominates over the non-linear transfer function of the active elements.
Remember, for ideal opamps (gain infinite) the amplification factor is determined solely by the external resistors.

---------- Post added at 12:09 ---------- Previous post was at 11:06 ----------

In addition to the simple explanation as given above I like to add something.
As you probably know, the concept of negative feedback was introduced by H.F. Black in 1934. His only motivation was to reduce distortions introduced by amplifier non-linearities.
The principle can be described as follows:
Let’s assume that at the output of an amplifier without feedback the amplitude of the positive half-wave of a sinusoidal signal is larger than the negative amplitude (due to non-linearities of the internal transfer characteristic).
Now, when negative feedback is provided, the amplifier „sees“ the difference between the input and the feedback signal. For larger output amplitudes this difference results in a smaller value than in the opposite case. As a consequence, this reduced value will be more amplified than the negative half-wave (due to the internal non-linearity, which still exist).
Thus, there is something like „redistortion“ back to the input waveform, which was assumed to be symmetrical.
As you know, as another consequence, the gain of the complete arrangement is reduced if compared with the non-feedback case.

 

[shilpashetty]

thank you so much LvW
it's so clear