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EUT 1040

EUT 1040. Lecture 4: Operational Amplifiers. Differential Amplifier. Not Practical Prior to IC Fabrication 2 Inputs, Output is A v *(V 1 - V 2 ). Common Mode Rejection. Differential Amps won’t Amplify Signals that are Common to both Inputs. Operational Amplifier. Three Stages:

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EUT 1040

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  1. EUT 1040 Lecture 4: Operational Amplifiers

  2. Differential Amplifier • Not Practical Prior to IC Fabrication • 2 Inputs, Output is Av*(V1 - V2)

  3. Common Mode Rejection • Differential Amps won’t Amplify Signals that are Common to both Inputs

  4. Operational Amplifier • Three Stages: • Differential Amplifier (Input Stage) • Voltage Amplifier (High Gain) • Output Stage (low output impedance)

  5. Op Amp Characteristics • High Input Impedance ( 1 M-Ohm) • Low Output Impedance (100 Ohms) • High Voltage Gain (A = 100,000) • 2 Differential Inputs • Inverting Input (V-) • Non-Inverting Input (V+)

  6. Equivalent Circuit Model • Differential Input Voltage determines Output Voltage

  7. Ideal Op Amp • Input Impedance is Infinite (No input Current, I- = I+ = 0) • Voltage Gain is Infinite (A = Infinity) • Inverting and Non-inverting inputs at equal potential (V+ = V- )

  8. Feedback • Open Loop Voltage Gain is so High that External Feedback is always used • Output Signal is Fed Back to an Input Terminal

  9. Analysis of Ideal Op Amp Circuits • Set V- = V+ and I- = I+ = 0 • Write Nodal Equation(s)

  10. Basic Op Amp Circuits • Voltage Follower: Impedance Matching or Isolation • Unity Gain: Vout = Vin

  11. Inverting Amplifier • Vout = -(R2/R1)*Vin

  12. Non-Inverting Amplifier • Vout = Vin*(R1+R2)/R1

  13. Summing Amplifier • Vout = -(V1*Rf/R1 + V2*Rf/R2 + V3*Rf/R3)

  14. Difference Amplifier • Vout = (V2-V1)*R2/R1

  15. Analysis of the Voltage Follower • Provides “Current Isolation” – No Power Drawn from Input Circuit

  16. References • Heathkit, Electronic Circuits, EB-6104A, 2002 • Alexander, Fundamentals of Circuit Analysis – 2nd Edition, McGraw-Hill, 2004

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