Reference is made to
http://www.allaboutcircuits.com/vol_3/chpt_4/12.html
(Volume III-Semiconductors, Biplar Junction Transistors, Feedback)
...negative feedback drives it the opposite direction: toward a point of stability.
An amplifier circuit equipped with some amount of negative feedback is not only more stable, but....
...the advantages of stability, lower distortion, and greater bandwidth are worth the tradeoff in reduced gain for many applications.
Also reference is made to:
http://www.allaboutcircuits.com/vol_3/chpt_8/12.html
(Volume III-Semiconductors, Operational Amplifiers, Positive feedback )
First paragraph:
Negative feedback makes all these circuits stable and self-correcting.
Correction:
When using the term stability it is necessary to discriminate between static and dynamic stability - that is between dc stability of the operating point (against tolerances and other uncertainties) and dyamic stability (against oscillations).
This is important because - in contrast to the above quoted statements - negative feedback DECREASES dynamic stability properties.
(Otherwise, no internal phase compensation would be necessary for opamps).
In fact, each negative feedback turns into positive feedback for increasing frequencies. Based on this observation the classical definitions for stability margins are formulated.
In summary: Negative feedback improves dc stability BUT deteriorates dynamic ac stability at the same time.
http://www.allaboutcircuits.com/vol_3/chpt_4/12.html
(Volume III-Semiconductors, Biplar Junction Transistors, Feedback)
...negative feedback drives it the opposite direction: toward a point of stability.
An amplifier circuit equipped with some amount of negative feedback is not only more stable, but....
...the advantages of stability, lower distortion, and greater bandwidth are worth the tradeoff in reduced gain for many applications.
Also reference is made to:
http://www.allaboutcircuits.com/vol_3/chpt_8/12.html
(Volume III-Semiconductors, Operational Amplifiers, Positive feedback )
First paragraph:
Negative feedback makes all these circuits stable and self-correcting.
Correction:
When using the term stability it is necessary to discriminate between static and dynamic stability - that is between dc stability of the operating point (against tolerances and other uncertainties) and dyamic stability (against oscillations).
This is important because - in contrast to the above quoted statements - negative feedback DECREASES dynamic stability properties.
(Otherwise, no internal phase compensation would be necessary for opamps).
In fact, each negative feedback turns into positive feedback for increasing frequencies. Based on this observation the classical definitions for stability margins are formulated.
In summary: Negative feedback improves dc stability BUT deteriorates dynamic ac stability at the same time.