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Lecture 4: Operational Amplifiers What can you do with infinite gain? Some History Fairchild 0.60 Inches 1964: The First Linear IC The µA702 Op-Amp 12 Transistors Designer: Bob Widlar 1965: A Best-Seller The µA709 Op-Amp 14 Transistors Designer: Bob Widlar

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lecture 4 operational amplifiers

Lecture 4: Operational Amplifiers

What can you do with infinite gain?

Introduction to Engineering Electronics

STOLEN FROM K. A. Connor

some history
Some History

Fairchild

0.60 Inches

1964: The First Linear IC

The µA702 Op-Amp

12 Transistors

Designer: Bob Widlar

1965: A Best-Seller

The µA709 Op-Amp

14 Transistors

Designer: Bob Widlar

Introduction to Engineering Electronics

STOLEN FROM K. A. Connor

2 minute quiz name section date
2 Minute QuizName_______ Section________ Date_________
  • What is the voltage measured by the blue probe?

Introduction to Engineering Electronics

STOLEN FROM K. A. Connor

what can you do with infinite gain
What can you do with infinite gain?
  • The goal of amplifier designers: huge gain.
  • What are the problems and opportunities associated with infinite gain?
  • First, we need a model.

Introduction to Engineering Electronics

STOLEN FROM K. A. Connor

op amp
Op-Amp

Introduction to Engineering Electronics

STOLEN FROM K. A. Connor

ideal op amp model
Ideal Op-Amp Model
  • Gain is infinite
  • Input resistance is infinite
  • Output resistance is zero
  • Input voltage is zero
  • Input current is zero

Introduction to Engineering Electronics

STOLEN FROM K. A. Connor

ideal op amp continued
Ideal Op-Amp Continued
  • Bandwidth is also infinite. Thus, an ideal op-amp works the same at all frequencies.

Introduction to Engineering Electronics

STOLEN FROM K. A. Connor

feedback
Feedback
  • Like most engineered systems, the op-amp uses feedback to realize its potential value.
  • Feedback comes in two forms
    • Positive Feedback
    • Negative Feedback
  • It seems like positive feedback might be best, but negative feedback makes the op-amp work

Introduction to Engineering Electronics

STOLEN FROM K. A. Connor

feedback examples from a zoology course
Feedback Examples From a Zoology Course
  • You just ate a Krispy Kreme donut and your blood glucose levels are on the rise. In response to this rise, the pancreas is releasing insulin into the blood stream stimulating storage of glucose. As a result, blood glucose levels begin to drop. Is this an example of positive or negative feedback?
  • A woman is in labor, pressure receptors in the birth canal send messages to her brain that result in increased contraction of the uterus and increased pressure in the birth canal. Is this positive or negative feedback?

Introduction to Engineering Electronics

STOLEN FROM K. A. Connor

feedback valve example
Feedback: Valve Example
  • As the water nears the specified level, the valve is closed.
  • Negative feedback is most commonly used to control systems.

Introduction to Engineering Electronics

STOLEN FROM K. A. Connor

golden rules for op amps
Golden Rules for Op-Amps
  • The output attempts to do whatever is necessary to make the voltage difference between the two inputs zero. (Negative Feedback is Required)
  • The inputs draw no current.

Introduction to Engineering Electronics

STOLEN FROM K. A. Connor

positive and negative feedback
Positive and Negative Feedback
  • Connecting the output to the positive input is positive feedback
  • Connecting the output to the negative input is negative feedback

Introduction to Engineering Electronics

STOLEN FROM K. A. Connor

op amp configurations
Op-Amp Configurations
  • Buffer or Voltage Follower
    • No voltage difference between the output and the input
    • Draws no current, so it puts no load on the source
    • Used to isolate sources from loads

Introduction to Engineering Electronics

STOLEN FROM K. A. Connor

op amp configurations14
Op-Amp Configurations

V2

  • Non-Inverting Amplifier
    • No voltage difference between inputs
    • Resistors act like voltage divider

Introduction to Engineering Electronics

STOLEN FROM K. A. Connor

op amp configurations15
Op-Amp Configurations
  • Non-Inverting Amplifier Continued
    • Combining the two equations for the voltages gives us the relationship between input and output

Note that this formula uses different variables in the lab write up

Introduction to Engineering Electronics

STOLEN FROM K. A. Connor

op amp configurations16
Op-Amp Configurations

V2

  • Inverting Op-Amp
    • Current through R1 equals the current through Rf
    • No current in the inputs
    • The voltage at both inputs is zero

Introduction to Engineering Electronics

STOLEN FROM K. A. Connor

op amp configurations17
Op-Amp Configurations
  • Inverting Op-Amp Continued
    • Current through R1
    • Current through Rf

Introduction to Engineering Electronics

STOLEN FROM K. A. Connor

2 minute quiz name section date18
2 Minute QuizName______ Section_______ Date________
  • What is the voltage measured by the green probe?

Introduction to Engineering Electronics

STOLEN FROM K. A. Connor

op amp configurations19
Op-Amp Configurations
  • Why the minus sign for the current through Rf?
    • The convention for Ohm’s Law is that the current flows from the high voltage to the low voltage for a resistor
    • Here the current flows from the low voltage (ground) to the high voltage (VO)

Introduction to Engineering Electronics

STOLEN FROM K. A. Connor

op amp configurations20
Op-Amp Configurations
  • Inverting Op-Amp Continued
    • The current through R1 must equal the current through R2 since there is no current in the inputs.
    • Combining the two equations for the currents

Introduction to Engineering Electronics

STOLEN FROM K. A. Connor

op amp configurations21
Op-Amp Configurations
  • Inverting Summing Amplifier
    • Each input resistor contributes to the current.

Introduction to Engineering Electronics

STOLEN FROM K. A. Connor

op amps practical issues
Op-Amps: Practical Issues
  • Op-Amps require power
    • 741 requires plus and minus 15V
    • Others may require only positive or both positive and negative voltages
    • Output voltage is limited to
    • Usually filter capacitors are connected to power to reduce noise

Introduction to Engineering Electronics

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op amps practical issues23
Op-Amps: Practical Issues
  • We use real op-amps: 741
  • Note the pin connections for the IC

Note: Literally a Black Box

Introduction to Engineering Electronics

STOLEN FROM K. A. Connor

op amps practical issues24
Op-Amps: Practical Issues
  • Note the pins (not all are used)
  • Extra resistor corrects offset problem

Introduction to Engineering Electronics

STOLEN FROM K. A. Connor

slide25
ICs come in many types of packages. We will use the 8-pin, dual-in-line or DIP package
  • Note the other offset nulling circuit

Introduction to Engineering Electronics

STOLEN FROM K. A. Connor

where will you see this information next
Where Will You See This Information Next?
  • Op-amps: Many Courses Including
    • ECSE-2010 Electric Circuits
    • ECSE-2050 Analog Electronics
  • Feedback and Control
    • ENGR-2350 Embedded Control
    • ECSE-4440 Control Systems Engineering
    • ECSE-496x Control Systems Design

Introduction to Engineering Electronics

STOLEN FROM K. A. Connor

embedded control
Embedded Control
  • Studio Classroom

Introduction to Engineering Electronics

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slide28

http://litec.rpi.edu

Introduction to Engineering Electronics

STOLEN FROM K. A. Connor

feedback and control example
Feedback and Control Example
  • The inverted pendulum is like balancing a baseball bat

Introduction to Engineering Electronics

STOLEN FROM K. A. Connor

inverted pendulum experiment
Inverted Pendulum Experiment

http://www.univ-valenciennes.fr/LAMIH/pendule/english/index.html

Introduction to Engineering Electronics

STOLEN FROM K. A. Connor

magnetic levitation
Magnetic Levitation
  • Trains can magnetically fly over a roadbed with position sustained by some kind of control system
  • Our next lab is on maglev

Introduction to Engineering Electronics

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more magnetic levitation
More Magnetic Levitation

Introduction to Engineering Electronics

STOLEN FROM K. A. Connor

2 minute quiz name section date33
2 Minute QuizName_______ Section________ Date__________
  • What is the voltage measured by the red probe?

Introduction to Engineering Electronics

STOLEN FROM K. A. Connor

answers
Answers
  • The green probe: 10V
  • The red probe: 1V
  • The blue probe: 0V
  • Voltage Divider:

Introduction to Engineering Electronics

STOLEN FROM K. A. Connor

engineering ethics
Engineering Ethics
  • Electrical and Computer Engineers do not usually face immediate ethical issues involving public health and safety
  • System control is one of many exceptions
  • From the IEEE Code of Ethics
    • We agree to accept responsibility in making engineering decisions consistent with the safety, health and welfare of the public, and to disclose promptly factors that might endanger the public or the environment;
  • http://www.iit.edu/departments/csep/eac/post_workshop.html

Introduction to Engineering Electronics

STOLEN FROM K. A. Connor