ME 6405

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ME 6405 Intro to MechatronicsOperational
Amplifiers
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Table of Content
Overview Theory Basic circuits Advantages
/ Disadvantes Applications

1. Overview
2. Theory of an OP-AMP
3. Basic circuits
4. Advantages / Disadvantages
5. Applications

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Overview
Overview Theory Basic circuits Advantages
/ Disadvantes Applications

• Definition A standard analog circuit component
  with two inputs, one output and a very high
  voltage gain.1
• Typically used for amplification, impedance
  matching and mathematical operations

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History of the OP AMP
Overview Theory Basic circuits Advantages
/ Disadvantes Applications

• Developed in the early 1940s
• Before the invention of the transistor made of
  vaccum tubes
• Became smaller with tranisistors
• Today small, inexpensive integrated circuits

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Schematics of an OP AMP
Circuit Design of an OP AMP
Overview Theory Basic circuits Advantages
/ Disadvantes Applications

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Pin assignment of the IC
Overview Theory Basic circuits Advantages
/ Disadvantes Applications
Pin Configuration (1) Offset (Typically Not
Used) (2) Inverting Input (3) Non-Inverting
Input (4) Low Supply (5) Offset (Typically Not
Used) (6) Output (7) High Supply (8) Not
Connected
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Properties of an OP-AMP

• Properties of the ideal
• OP-AMP
• Rin is infinite
• Rout is zero
• Amplification Vout / Vin is infinite
• Unlimited bandwidth
• Zero output voltage at zero input difference

• Properties in reality
• Finite input resistance
• Small, but not zero output resistance
• Finite gain / Saturation
• Finite bandwidth

Overview Theory Basic circuits Advantages
/ Disadvantes Applications

1. THE OP AMP WILL TRY TO MAKE THE VOLTAGE
   DIFFERENCE BETWEEN THE TWO INPUTS TO ZERO!
2. THE CURRENT INTO THE OP AMP IS ALWAYS ZERO

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Typical Values of an OP AMP
Overview Theory Basic circuits Advantages
/ Disadvantes Applications
Property Ideal Real
Voltage Gain 8 105 - 109
Input Resistance Input Current 8 ? 0 A 106 ? 10-12 10-8 A
Output Resistance 0 ? 100 1000 ?
Bandwidth 8 Phaseshift at high frequencies
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Basic circuits
Overview Theory Basic circuits Advantages
/ Disadvantes Applications

• Comparator e.g. temperature sensor
• Linear amplifier
• Linear inverting amplifier
• Impedance matching
• Summing Amplifier
• Subtractor
• Integrator
• Differentiator
• Schmitt Trigger e.g. two stage comperator

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Nonlinear Usage - Comparator
Overview Theory Basic circuits Advantages
/ Disadvantes Applications
The nonlinear usage always works without feedback
Example with reference voltage UN 0
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Linear Usage
Overview Theory Basic circuits Advantages
/ Disadvantes Applications
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Inverting Amplifier
Overview Theory Basic circuits Advantages
/ Disadvantes Applications

• Input impedance infinite, therefore no current in
  the OP AMP
• V - V- 0

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Non Inverting Amplifier
Overview Theory Basic circuits Advantages
/ Disadvantes Applications

• Input impedance infinite, therefore no current in
  the OP AMP
• V V-

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Summing Amplifier
Overview Theory Basic circuits Advantages
/ Disadvantes Applications

• Input impedance infinite, therefore no current in
  the OP AMP
• V - V- 0

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Impedance matching
Overview Theory Basic circuits Advantages
/ Disadvantes Applications
Vin Vout
OP AMP tries to make the voltage difference
between the inverting and the non inverting input
to zero
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Subtracting Amplifier
Overview Theory Basic circuits Advantages
/ Disadvantes Applications
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Integrator
Overview Theory Basic circuits Advantages
/ Disadvantes Applications

• Input impedance infinite, therefore no current in
  the OP AMP
• V - V- 0

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Integrator (II)
Overview Theory Basic circuits Advantages
/ Disadvantes Applications
Integrate
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Differentiator
Overview Theory Basic circuits Advantages
/ Disadvantes Applications
Make the same calculation as with the integrator,
just switch the resistor and the capacitor
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Schmitt Trigger
Overview Theory Basic circuits Advantages
/ Disadvantes Applications
Two stage level detector
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Advantages / Disadvantages
Overview Theory Basic circuits Advantages
/ Disadvantes Applications

• Advantages cheap, easy to use, effective
• Disadvantages Ideal not possible, phase shift at
  high frequencies
• Applications A/D conversion, Filtering, any
  digital circuit

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Applications D/A Converter
Overview Theory Basic circuits Advantages
/ Disadvantes Applications
Picture from Class Lecture D/A Conversion
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Low Pass
Overview Theory Basic circuits Advantages
/ Disadvantes Applications
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Application - Rectifier
Overview Theory Basic circuits Advantages
/ Disadvantes Applications
The Schmitt Trigger can be used to rectify a
signal in order to get a clock
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Sources

• 1 www.siemensauto.com/glossaries/electronics_gloss
  ary.html
• http//www.ele.uri.edu/Courses/ele343/low.pass/
• Pictures of example circuits taken from
• http//www.fh-landshut.de/wlf/schT/Vorlesung/ST_
  3.pdf
• http//www.elektronik-kompendium.de/sites/bau/020
  9092.htm
• Some pictures taken from Garcia-Rivera, Newby,
  Rogge, Presentation on the 25th of September 2003
  in the ME 6405 class (www.me.gatech.edu/mechatroni
  cs_course)

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• Questions?

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• An output of the Gogia, Sandhu, Koenig brain
  factory