Lect_11 - ECE ECE442 SolidStateDevices&Circuits...

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CE 442 ECE 442 Solid State Devices & Circuits 11. Operational Amplifiers Jose E. Schutt-Aine Electrical & Computer Engineering University of Illinois jschutt@emlab.uiuc.edu 1 Jose E. Schutt Aine–ECE 442
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Operational Amplifiers Universal importance (e.g. amplification from microphone to loudspeakers) General terminal configuration with bias 2 Jose E. Schutt Aine–ECE 442
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Operational Amplifiers ) A v v Gain= A 21 () out vA ommon configuration with bias Common configuration with bias implied but not shown ignaling Signaling 1. Differential input stage ifference between input is amplified 3 Jose E. Schutt Aine–ECE 442 2. Difference between input is amplified
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Operational Amplifiers Ideal Op Amp 1. Infinite input impedance 2. Zero output impedance finite open op gain A f 3. Infinite open-loop gain A Î inf 4. Infinite CMMR or zero common-mode gain finite bandwidth 5. Infinite bandwidth Also, op amps are dc (or direct coupled) amplifiers since they are expected to amplify signals with frequency as low as DC. 4 Jose E. Schutt Aine–ECE 442
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Differential & Common-Mode Signals - Differential input signal v ID =v 2 -v 1 - Common-mode input signal v m =0.5(v +v ) ICm 1 2 1 2 ID ICm v vv =− 2 2 ID ICm v =+ 5 Jose E. Schutt Aine–ECE 442
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Operational Amplifiers Ideally, v ICM should be zero to achieve high CMMR. Amplifier will amplify the difference between the two input signals 6 Jose E. Schutt Aine–ECE 442
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Practical Considerations The output voltage swing of an op amp is limited by the DC power supply. Since op amp can exhibit high gain, ower supply voltage fluctuations must be minimized power supply voltage fluctuations must be minimized Î use decoupling capacitors from power supply 7 Jose E. Schutt Aine–ECE 442
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Inverting Configuration Terminal 2 is tied to ground We introduce R F (or R 2 ) to reduce gain (from inf) When R F is connected to terminal 1, we talk about negative feedback. If R F is tied to terminal 2, we have positive feedback 8 Jose E. Schutt Aine–ECE 442 ,p
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Inverting Configuration Need to evaluate v o /v I ssume ideal Op mp Assume ideal Op-Amp 1 () 0 o v vv = −= Since gain is infinite: 21 A 2 , 0 Thus v v == Note: A is open-loop gain v 1 is virtual ground 12 1 1 II v i R = = 9 Jose E. Schutt Aine–ECE 442 11 RR
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This note was uploaded on 09/07/2011 for the course ECE 442 taught by Professor Schutt-aine during the Summer '08 term at University of Illinois at Urbana–Champaign.

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Lect_11 - ECE ECE442 SolidStateDevices&Circuits...

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