ECE 4991 Electrical and Electronic Circuits Chapter 8

2 Where are we? Chapter 2 - The basic concepts and practice at analyzing simple electric circuits with sources and resistors Chapter 3 – More harder networks to analyze and the notion of equivalent circuits Chapter 4 – Capacitors and inductors added to the mix Chapter 5 – Analyzing transient situations in complex passive networks Chapter 8 – New subject – the wonders of operational amplifiers as system elements Chapter 9 – Introduction to semiconductors – the basics and diodes – more network analysis Chapter 10 – Bipolar junction transistors and how they work – now you can build your own op amp

3 What’s Important in Chapter 8 1.Definitions 2.Op Amp Basics 3.Inverting Amplifiers 4.Summing Amplifiers 5.Non-inverting Amplifiers 6.Voltage Followers 7.Diff Amps 8.Integrators 9.Differentiators

4 1. Definitions Operational Amplifier Open-loop Feedback Inverting (input) Non-inverting (input) Open-loop voltage gain

5 2. Op Amp Basics An operational amplifier is an IC “engine” that can support many applications Defining characteristics –Amplifies difference between two input voltage –Extremely high gain –Extremely high input resistance –Extremely low output resistance

6 Diagramming an Op Amp + Pwr _ Pwr Output Non-inverting Input Inverting Input + _

7 Design Assumptions Two main design assumptions for op amp applications using negative feedback 1.Zero input current 2.Input voltages forced to be equal

8 3. Inverting Amplifier + input grounded Input signal to (–) input through R S Output fed back to (–) input through R F Gain = - R F /R S + _

9 Inverting Amplifier Practice Design an inverting amplifier with a gain of _

10 Inverting Amplifier Practice Given the following resistors to work with – 1KΩ, 1KΩ, 3KΩ, 20KΩ, 30KΩ – design an inverting amp with gain _

11 4. Summing Amplifier + input grounded Several input signals to (–) input through R S ’s Output fed back to (–) input through R F V out = -  (R F / R S i ) v s i + _

12 Summing Amplifier Practice Design an amplifier with V out = - 50 (v 1 + v 2 + v 3 ) + _

13 Summing Amplifier Practice Design an amplifier with V out = - (20v 1 +30v v 3 ) + _

14 5. Non-Inverting Amplifiers Ground the (-) input through R S Signal input to + input through any R Output fed back to (-) input through R F Gain is 1 + R F / R S + _

15 Non-Inverting Amplifier Practice Design a non-inverting amp with gain = 10 + _

16 Non-Inverting Amplifier Practice Resistor collection is 20Ω, 50Ω, 100Ω, 100Ω, 300Ω, 300Ω, 500Ω Design a non-inverting amplifier with a gain of 5 + _

17 6. Voltage Follower Output fed back directly to (-) input Signal input directly to + input V out = v S + _

18 What’s a Voltage Follower For? Op amp input impedance very high Op amp output impedance very low Voltage followers buffer sensitive circuits or circuit elements Also used for driving speakers, long cables, etc

19 7. Differential Amplifiers V 1 input fed to (-) input through R 1 V 2 input fed to + input through a different R 1 Output tied back to (-) input through R 2 + input tied to ground through R 2 V out = (R 2 /R 1 ) (V 2 – V 1 ) + _

20 Differential Amplifier Practice Design a diff amp with V out = 50 (V 2 – V 1 ) + _

21 Differential Amplifier Practice Design a diff amp with V out = 200 sin t – 600 cos 3t + _

22 Differential Amplifier Practice Design a diff amp with V out = 40 sin t – 10 V 1 + _

23 8. Integrating Amplifiers Signal input fed to (-) input through R S Output tied back to (-) input through C F + input tied to ground V out = - (1/R S C F )  V S dt + _

24 Integrating Amplifier Practice V S = 4 sin  t, R S = 100 , C F = 50  F V out = ? + _

25 Integrating Amplifier Practice V out = t 4 Volts V S = ?, R S = 1K , C F = ? + _

26 9. Differentiating Amplifiers Signal input fed to (-) input through C S Output tied back to (-) input through R F + input tied to ground V out = - R F C S dV S /dt + _

27 Differentiating Amplifier Practice V out = - R F C S dV S /dt Design a differentiating amplifier with V out = 30 sin  t + _

28 Differentiating Amplifier Practice V out = - R F C S dV S /dt V S = 25 sin 2t, R F = 100 , C S = 10  F V out = ? + _

29 Op Amp Practice + _

30 Op Amp Practice + _

31 Op Amp Practice + _

32 Op Amp Practice + _

33 Op Amp Practice + _

34 Op Amp Practice + _