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Operational Amplifier

Operational Amplifier. Nearly ideal High gain high input impedance low output impedance stable Simple for circuit construction Goals Learn basic characteristics of operational amplifier. Build and characterize amplifier circuits. http://www.uoguelph.ca/~antoon/gadgets/741/741.html

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Operational Amplifier

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  1. Operational Amplifier • Nearly ideal • High gain • high input impedance • low output impedance • stable • Simple for circuit construction • Goals • Learn basic characteristics of operational amplifier. • Build and characterize amplifier circuits. http://www.uoguelph.ca/~antoon/gadgets/741/741.html http://ourworld.compuserve.com/homepages/Bill_Bowden/opamp.htm http://www.allaboutcircuits.com/vol_3/chpt_8/1.html

  2. Pin Configuration • Notch • Counterclockwise numbering • Input • #2 V-; #3 V+ • Output • #6 Vout • Power supply • #4 –VDD; #7 +VCC • #1, #5, offset adjustment

  3. Key Characteristics • Output saturation voltages • Output voltage never surpasses power supply • Linear amplifier • Nonlinear, saturation • Not always bad! • Output impedance limitation • Finite load driving capability • Bandwidth limitation - Slew rate • Finite speed or response time • Gain dependent http://www.amplifier.cd/Tutorial/Slew_Rate/SlewRate.htm • Offset compensation • Cascading

  4. Circuit • Two Input Nodes What will happen if the output is connected to the non-inverting input?

  5. Dual Power Supply • Set voltages, Limit current Earth Ground Do NOT use -15 to pin 4 +15 to pin 7 Ground Reference Don’t let it dangle

  6. Open Loop • R2 = , R1 = 0 • Ground non-inverting input • Signal applied to inverting input • Differential gain > 10000 • Driven into saturation • Measure the output impedance with a load resistor • Output reduced by 2

  7. Waveform Vsat

  8. Unit Gain Amplifier • Connect output to inverting input • Do not ground the inverting input • Signal applied to non-inverting input • Gain = 1 • How fast can the output change? • Slew rate, V / t; around 0.6 V/sec • Are inverting and non-inverting input ports symmetric? What will happen when there is a feedback from output to non-inverting input?

  9. Waveform Slew Rate

  10. Inverting Amplifier • Feedback R2 • Ground pin 3 • Virtual ground at pin 2 • Input impedance > R1, R2 • Output impedance < R1, R2 • Av = - R2 / R1

  11. Waveform

  12. Bode Plot

  13. Frequency Response • Gain vs. frequency plot • Amplify to DC • -3dB frequency • Higher gain, less bandwidth • Gain bandwidth product

  14. Non-Ideal Characteristics • Offset • DC input is zero but output is not zero • Adjust using pins 1 and 5

  15. Non-Ideal Characteristics • Finite input impedance • Leakage current • Symmetric input • Common mode rejection ratio • Differential input • Gain • Common input • No gain http://www.mines.edu/Academic/courses/physics/phgn217/lab8/lect13/sld001.htm

  16. Circuit to Build

  17. Measurements • Saturation voltages • Output impedance • Slew rate • Gain vs frequency • Bandwidth and gain correlation • In cascaded amplifiers, how to optimize the bandwidth? • Output offset before and after adjustment

  18. Variations of Op Amp Circuit • Non-inverting amplifier

  19. Applications of Op Amp • Microphone pick up • Audio amplifier • Active filters • Log amplifier • Laser or LED driver • …

  20. Review • Pin assignments • Inverting input versus non-inverting input • Typical saturation voltage, output impedance, and slew rate • How to build an inverting amplifier? • How to adjust the gain? • Is the bandwidth gain dependent? • Gain bandwidth product

  21. Challenges • Can the operational amplifier be operated with a single power supply? • Can you build a summing amplifier or a subtracting amplifier? • What is the instrumentation amplifier? Can you build one by using 741s?

  22. Circuit Simulations

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