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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
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”

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





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.