What is the function of Inverting amplifier?
Why negative feedback is required?

 

An inverting amplifier produces a 180 deg phase shift in the signal, making it a mirror image of the original.

Any amplifier requires negative feedback. Without it, the output swing caused by the input signal will tend to go as far as the supply rail will let it. The feedback lets the output be proportioned to the input, so the gain will be predictible.

Wikipedia has an articles and references about negative feedback - http://en.wikipedia.org/wiki/Negative_feedback.

 

An inverting amplifier produces a 180 deg phase shift in the signal, making it a mirror image of the original.

Why have to produce a 180 degrees out of phase with the input signal? What is the usage?

 

Let me point you to the section of this site's Ebook that deals with common emitter amplifiers - http://www.allaboutcircuits.com/vol_3/chpt_4/5.html. The amplifier so made is inverting, as the output is 180 deg inverted from the input. Another way of saying it is that an inverting amplifier inverts the signal.

 

Why have to produce a 180 degrees out of phase with the input signal? What is the usage?

One example of use is on bridged amplifiers, where there are two amplifiers 180º out of phase supplying the signal to a common speaker. Both outputs are connected to the speaker that way. The purpose of this is to have twice the gain of each amplifier and the output power doubled, keeping the supply voltage low.

 

What is the function of Inverting amplifier?
Why negative feedback is required?

Can I bring to your attention the section on negative feedback in Volume III: http://www.allaboutcircuits.com/vol_3/chpt_8/4.html

Dave