EE3101 Design with Op Amps

1
EE3101 Design with Op Amps

• Your instructor prof. Jovan Jevti

3 years of teaching experience in academia 7
years of industry experience in semiconductors
and magnetic resonance imaging Ph.D. in
Electromagnetics / Semiconductors from The Ohio
State University
My best advice? The wisdom of the ages
REPETITIO MATER STUDIORUM EST
2
Please Introduce Yourself

• Name
• Major
• Pick one
• What attracts you to your chosen major?
• What are your expectations from the EE3101
  course?
• Any questions for me?
• Limit to 1 minute or less

3
Course Policies in a Nutshell

• Final mandatory
• 2 exams no makeup exams, missed counts 0
• 10 labs reports due next lab, makeup labs at my
  discretion
• Absences more than 2 labs or 6 lectures you
  drop or F
• Homework 25 credit reduction for each day late
• Grading Prereq quiz 3
• Homework 22
• Labs 30
• Exams 2x10
• Final 25

Please refer to the handouts for details
4
Communication
The course weblog should be up and running in a
matter of days. This should be your central point
for course related information and
discussions http//myweb.msoe.edu/jevtic/EE3101
Keep the lines of communication open. Any
concerns, contact me early. For private and
confidential matters use e-mail jevtic_at_msoe.edu
5
Whats this Course About Anyway?

• Is it about
• Op Amp Design
• or Op Amp Circuits
• or Op Amp Applications
• or Design with Op Amps?

And the surprise answer is
FEEDBACK!
6
Why Focus on Feedback?

• Op amp based circuits are the most versatile
  building block of analog electronics.
• The versatility stems from the great variety of
  feedback configurations that a designer can
  implement around any one op amp device.
• The ability to meet high performance requirements
  in a specific application is due to the ingenuity
  of the feedback design and the near ideal
  characteristics of modern op amp devices.
• What you learn about feedback in this course,
  will serve you well in many other cases where the
  feedback plays a key role from electronic
  control systems to human physiology.

7
An Everyday Example of Feedback

• Audio feedback
• A high-pitched, loud, squealing, screeching
  sound that may occur during a music concert.

8
The Audio Feedback Experiment
9
This Raises Some Questions
How is the pitch of the sound related to the
distance between the radios? Any ideas why? The
feedback loop contains two very different kinds
of waves. Can you name them? What can be done to
stop the squeal? Does any of the proposed methods
affect the desired radio communication?
A Practical Note Feedback often creeps in along
unexpected paths which can be very difficult to
identify, understand, and may be beyond our
control.
10
Positive Feedback

• Audio feedback is a positive feedback. Circuits
  with positive feedback are prone to oscillations
  as weve seen in the experiment.
• However, the positive feedback has some
  remarkable properties which have made it the
  mainstay of early electronics from 1900-1930s.
• The positive feedback can increase the gain of an
  electronic detector device 100s of times!
• Lets briefly review the early applications of
  the positive feedback in electronics as this sets
  the stage for the negative feedback.

11
The Age of Coherers and Vacuum Tubes

• Before ICs,
• before transistors,
• before vacuum tubes
• there were coherers!

coherer
coherer receiver
Problem Low sensitivity
12
Regenerative Receiver
Regenerative (positive feedback) receiver could
easily achieve a 100-fold improvement in
sensitivity. Nikola Tesla 1899 (using a coherer
device) Edwin Armstrong 1911 (using a vacuum
tube device)
13
Where is the Regenerative Circuit Today?

• Enhancing the gain with the use of a positive
  feedback was the technique that made the radio,
  telephony, and electronics possible in the age of
  low sensitivity electronic devices.
• This led to a rapid increase in the number of
  telephone subscribers, as well as to many new
  applications which required more complex and more
  accurate electronics than it was possible to
  achieve with an inherently over-sensitive
  regenerative circuit.
• In the 1930s, the scene was set for a major
  breakthrough in electronics whose conceptual and
  practical impact is still felt in all of
  engineering. Well talk about it tomorrow.

14
Assignments

• PREREQ QUIZ will be handed out on Thursday
• HOMEWORK none today
• READING - Preface (1st page only)