1. ECE 1270: Introduction to Electric Circuits
Lecture 13:
Operational Amplifiers
Part 2
Chapter 5
The Operational Amplifiers
Sections

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

3. 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

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

5. Non-inverting Amplifier
1) Output and Input signals have same polarity (0 ° phase shift)
2) Non-inverting Amplifier provides positive voltage gain

6. AP 5.4 (Use the formula) a) Find the output voltage when Rx=60 kΩ
b) How large can Rx be before saturation

7. Voltage Follower (Buffer)
Suppose Rg=Rf=0 (short), Rs=Inifinite (open)
Circuit becomes voltage follower, e.g. vo=vi
Q: Why should we use a voltage follower (Gain=1)?

8. Summing Amplifier
A Summing Amplifier combines several inputs and outputs the weighted sum of the inputs

9. Summing Amplifier: Application
Digital to Analog Converter (DAC)
Q: Why do we use DAC?

10. p5.17: Design of a Summing AmpVa Vb Vc Vd Ra Rb Rc Rd
Design the Summing Amplifier so that

11. Difference (Differential) Amplifier
Differential Amp rejects
Common-mode signal (noise or DC)
If Ra/Rb=Rc/Rd (same ratio) then...
A Difference (Differential) Amplifier amplifies the difference between two input signals but rejects signals common to the inputs

12. Differential Amplifier: Application
Instrumentation Amplifer (IA)
An Instrumentation Amplifier (IA) is used for precise measurement and amplification with noise reduction in sensors and data acquisition systems

13. AP5.5a: Differential Amplifier
Find range of Va that results in linear operation (avoids saturation)
Use Eq (5.22) (because Ra/Rb ≠ Rc/Rd )