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Operational Amplifiers Digital Simulation

Operational Amplifiers Digital Simulation. Nate Moehring. Operational Amplifiers. Used in amplifiers, attenuators, and filters Ideal Properties of an Op Amp: Infinite open-loop gain, A ol = infinity Infinite input impedance, R in = infinity Zero output impedance, R out = 0

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Operational Amplifiers Digital Simulation

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  1. Operational AmplifiersDigital Simulation Nate Moehring

  2. Operational Amplifiers • Used in amplifiers, attenuators, and filters • Ideal Properties of an Op Amp: • Infinite open-loop gain, Aol = infinity • Infinite input impedance, Rin = infinity • Zero output impedance, Rout = 0 • Zero noise contribution • Zero DC output offset • Infinite bandwidth, infinite frequency response • Both differential inputs stick together

  3. Why use op amps? • Extremely high gain (10,000x) • Infinite input resistance good for adding multiple sources (0 current = 0 voltage drop) • Develop high pole filters

  4. Example • Passive Band Pass

  5. Example • Active Band Pass

  6. Example • Active Band Pass w/ amplifier

  7. Op Amp configurations Comparator • Rails +/- to higher input • (Takes difference • Multiplies by 10,000)

  8. Op Amp configurations Inverting Gain • Vo = -Vi(Rf/Ri) • (Feedback loop creates 180oout of phase signal that eliminates large Aol)

  9. Op Amp configurations Non - Inverting Gain • Vo = Vi(1 + Rf/Ri) • (Feedback line must always go to negative input. Otherwise, we would be summing infinitely.)

  10. Op Amp configurations Buffer – Isolation Amplifier • Vo = Vi(1 + 0/) = 1 • Also called “follow me” amplifier.

  11. Op Amp configurations Filter • fc = 1/(2RC) • “Active”, although this filter is no better than a passive filter.

  12. Op Amp configurations Differential Amplifier • Vo = R2/R1(V2-V1) • “Subtractor”

  13. Op Amp configurations Summing Amplifier • Vo = V1(R3/R1) + V2(R3/R2) • “Adder”

  14. Parametric resultsw/ transient

  15. Parametric resultsw/ AC Sweep

  16. Transistors Bipolar Junction Transistors BJT (npn) • Uses a small amount of current to allow a large amount of current to pass through it. (Amplifier) (Flood gate) • Also used as “on/off” switch. (Transistor Transistor Logic (TTL)) • Bipolar.olb Collector Base Emitter

  17. NOT Gate These TTL representations are greatly simplified for logical interpretation and are not meant for actual implementation as seen here.

  18. AND Gate

  19. OR Gate

  20. Digital Simulation • Use Bias Point calculations manually changing VDCs • Use Bussed STIM sources to perform transient analysis. • Get digital components from 74ac (pro) or Eval library (student)

  21. Using STIM sources • Use STIM4 from source library • Draw bus wire • Place “Net Alias” ON bus, ie. A[0:3] • Use “Bus Entry” tool to extract lines • Name lines using Place “Net Alias” • Double click STIM4 to create pattern • Probe input and outputs • Run transient simulation

  22. Voter Problem • Build using 74xx logic gates • Input manually using VDC sources and view outputs using Bias Voltages • Input using STIM4 providing all possible input combinations.

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