Circuits & Electronics P21

Op Amps Positive Feedback 6.002 Fall 2000 Lecture 21 1 .Negative vs Positive Feedback Consider this circuit — negative feedback vIN R1 R2 – R1 vIN + + R – + vOUT = − 2 vIN – R1 and this — positive feedback + – R2 vIN + – R1 sis e aly pag an t ee nex s on + R2 “vOUT = − R vIN ” – 1 What’s the difference? Consider what happens when there is a pertubation… Positive feedback drives op amp into saturation: vOUT → ±VS Lecture 6.002 Fall 2000 21 2 .Static Analysis of Positive Feedback Ckt v IN + – R1 + – v + R2 v − R2 vOUT v IN + – R1 + – A(v + − v −...