Negative feedback is one of the most useful concepts in electronics, particularly
in op- amp applications. Negative feedback is the process whereby a portion of
the output voltage of an amplifier is returned to the input with a phase angle that
opposes (or subtracts from) the input signal. Negative feedback is illustrated in
Figure (9). The inverting (- ) input effectively makes the feedback signal 1800 out
of phase with the input signal.