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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

Operational AmplifiersDigital Simulation

Nate Moehring

Operational amplifiers
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

Why use op amps
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


  • Passive Band Pass


  • Active Band Pass


  • Active Band Pass w/ amplifier

Op amp configurations
Op Amp configurations


  • Rails +/- to higher input

  • (Takes difference

  • Multiplies by 10,000)

Op amp configurations1
Op Amp configurations

Inverting Gain

  • Vo = -Vi(Rf/Ri)

  • (Feedback loop creates

    180oout of phase signal

    that eliminates large Aol)

Op amp configurations2
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.)

Op amp configurations3
Op Amp configurations

Buffer – Isolation Amplifier

  • Vo = Vi(1 + 0/) = 1

  • Also called “follow me”


Op amp configurations4
Op Amp configurations


  • fc = 1/(2RC)

  • “Active”, although this

    filter is no better than a

    passive filter.

Op amp configurations5
Op Amp configurations

Differential Amplifier

  • Vo = R2/R1(V2-V1)

  • “Subtractor”

Op amp configurations6
Op Amp configurations

Summing Amplifier

  • Vo = V1(R3/R1) + V2(R3/R2)

  • “Adder”

Parametric results w transient
Parametric resultsw/ transient

Parametric results w ac sweep
Parametric resultsw/ AC Sweep


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




Operational amplifiers digital simulation

NOT Gate

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

Digital simulation
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)

Using stim sources
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

Voter problem
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.