Feedback Amplifier

Open-loop Gain: A

Feedback Factor: β

Loop Gain: Aβ

Amount of Feedback: (1+Aβ)

Gain of the Feedback Amplifier (Closed-loop Gain): Af = xo/xs = A/(1+Aβ)

 

Negative Feedback

The feedback signal xf is subtracted from the source signal xs

Negative feedback reduces the signal that appears at the input of the basic amplifier
The gain of the feedback amplifier Af is smaller than open-loop gain A by a factor of (1+Aβ) 

 

The loop gain A is typically large (Aβ>>1)

The gain of the feedback amplifier (closed-loop gain) Af = 1/β

The closed-loop gain is almost entirely determined by the feedback network (better accuracy of Af)

xf = xs(Aβ)/(1+Aβ) = xs (error signal xi = xs - xf)