1. ECE 1270: Introduction to Electric Circuits
Lecture 13:
Operational Amplifiers
Part 1
Chapter 5
The Operational Amplifiers
Sections 5.1,5.2, 5.3

2. Operational Amplifiers
Purpose
1) Amplify AC/DC voltage (or current).
2) Perform addition, subtraction, multiplication, division, differentiation, and integration of signals

3. Operational Amplifiers: Applications
1) Amplify audio signals
2) Filter unwanted signals (frequencies)
3) And many more...
Subwoofer
Filter
Audio Preamplifier

4. Operational Amplifiers
Pin Diagram
Positive
Power Supply
Negative
Power Supply

5. Operational Amplifiers
Symbol & Notation ip io in

6. OpAmp: Circuit Model vp vo vn vp vo vn Open loop gain
Output voltage in linear region vo vn
Open loop gain
(without feedback) vp
Input Resistance
Output Resistance vo + - vn

7. OpAmp Characteristicsvp vo + vn -
An Ideal Op amp has infinite open-loop gain, infinite input resistance and zero output resistance
When Op amp is connected in the circuit...
For an ideal OpAmp
vp = vn (voltages at positive input terminal and negative input terminal are equal to each other)
ip= in = 0 (currents entering the positive and negative input terminals are zero) vp ip vo vn in

8. Example 5.1 a) Find vo if va=1 V, vb=0 V
Simulate: 1) with va=1V and 2) with

9. AP5.1 a) a) Find vo if vs=0.4, 2.0, 3.5, -0.6, -1.6, -2.4
Q: Which values of vs will cause op amp to saturate?

10. p5.4 a) & (b) a) Find vo if va = 1.5 V and vb = 0 V40 5 2 10
a) Find vo if va = 1.5 V and vb = 0 V
b) Find vo if va = -0.5 V and vb = 0 V

11. Op-Amp Configurations
1) Inverting Amplifier
2) Non-inverting Amplifier
3) Voltage Follower (or buffer)
4) Summing Amplifier
5) Difference Amplifier

12. Inverting Amplifier
1) Output and Input signals have opposite polarity (180 ° phase shift)
2) Inverting Amplifier provides negative voltage gain

13. Example 5.2: Design of an Inverting Amplifier

14. p5.8: Design of an Inverting Amplifier