1. ECE 194 S’01 Introduction to Engineering II Arizona State University 1 The operational amplifier, cont.  Has a multitude of circuit applications  Linear applications  Inverter, summer, integrator, etc.  Non-linear applications  Comparator

2. ECE 194 S’01 Introduction to Engineering II Arizona State University 2 Classwork #2 Find v o

3. ECE 194 S’01 Introduction to Engineering II Arizona State University 3 Inverting summing amplifier

4. ECE 194 S’01 Introduction to Engineering II Arizona State University 4 Op amp non-linear applications The output voltage is a function of the input voltage difference Op amp can be forced to work in the linear region with feedback Without feedback, the operation is quite different

5. ECE 194 S’01 Introduction to Engineering II Arizona State University 5 The comparator  A comparator is a circuit that monitors two input voltages  One is called the reference voltage, and the other the input voltage  The output voltage depends upon the relation between the reference voltage and the input voltage, i.e., whether V in is larger or smaller than V ref  Op amps operated without feedback can act as comparators

6. ECE 194 S’01 Introduction to Engineering II Arizona State University 6 Comparator Reference voltage to positive input Reference voltage to negative input

7. ECE 194 S’01 Introduction to Engineering II Arizona State University 7 Comparator circuits Physical signals Physical outputs

8. ECE 194 S’01 Introduction to Engineering II Arizona State University 8 Generic comparator circuit Physical and electrical input signals Physical and electrical outputs

9. ECE 194 S’01 Introduction to Engineering II Arizona State University 9 Comparator circuits What are R A and R B ? Circuit components that convert physical signals to electrical signals by having electrical properties that change with external physical changes. Examples: Thermistors - temperature sensitive resistors Photoconductors - light sensitive resistors Strain gauges - strain sensitive resistors Microphones - sound sensitive components

10. ECE 194 S’01 Introduction to Engineering II Arizona State University 10 Comparator circuits Output component examples LEDs driven by op amp output Power transistor stages to drive LEDs, buzzers, relays Other amplifier stages Voltage to frequency converters Analog to digital converters Multimeters Motors Timers, clocks, recorders

11. ECE 194 S’01 Introduction to Engineering II Arizona State University 11 Additional circuit components Variable resistor = Diode R V = R 1 + R 2

12. ECE 194 S’01 Introduction to Engineering II Arizona State University 12 Additional circuit components Bipolar junction transistor Transistor Field effect transistor FET I C ≈ I E ICIC Large current (I B > 0) Zero (I B = 0) I D = I S IDID Large current (V G > 0) Zero (V G = 0)

13. ECE 194 S’01 Introduction to Engineering II Arizona State University 13 Additional circuit components Sensing resistor R = R(Temperature) R = R(Pressure) R = R(Light) Relay Electromechanical device - a small current is used to control a large current

14. ECE 194 S’01 Introduction to Engineering II Arizona State University 14 Example comparator circuit Light activated switch LED is on when input is below V ref Resistance of photoconductor decreases when illuminated

15. ECE 194 S’01 Introduction to Engineering II Arizona State University 15 Classwork Building upon ideas from previous circuit, design a Dark Activated Switch

16. ECE 194 S’01 Introduction to Engineering II Arizona State University 16 Classwork Build and test this circuit - use a voltmeter to measure voltages in circuit