Feedback in amplifiers (introductory)
Transistors and circuits · Physics
DC circuit
Interactive 3DElectrons drift around the loop — raise the voltage and watch the current obey Ohm's law.
Controls
Drag the sliders or type a value — the simulation updates live.
V
1V12V
Study notes
An amplifier has open-loop gain A = 2000 and distortion 8%. Negative feedback with β = 0.049 is applied. (a) Find the closed-loop gain. (b) Estimate the new distortion. (c) What happens if β is increased so that Aβ = 1? Solution: (a) A_f = A/(1 + Aβ) = 2000/(1 + 2000×0.049) = 2000/99 ≈ 20.2. (b) Distortion_f ≈ 8%/99 ≈ 0.08% — nearly a hundredfold cleaner. (c) At Aβ = 1 the denominator vanishes: the circuit becomes an oscillator (Barkhausen criterion) instead of an amplifier.