Basic Feedback Concept
where, A→Open loop gain; β → β→Feedback factor
Si → Input signal; Se → Error signal
Sf→Feedback signal
Gain with feedback
Af = A/1+Aβ for – ve feedback ; Af = A/1-Aβ for + ve feedback
Loop gain or return ratio
Loop gain = −Aβ
Return difference
• The difference between unity and loop gain is called return difference (D).
D = (1+Aβ)
• D is also called desensitivity.
Sensitivity
In case of negative feedback, if
dA/A → % change without feedback.
dAf /Af → % change with feedback.
dAf /Af = dA/A /(1+Aβ), i.e., reduction in sensitivity of amplifier.
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