CHAPTER 23 (4): OPERATIONAL AMPLIFIERS

Page 1: Introduction

• Copyright notice for the document by Tan Hua Joo & Wong WY, Singapore Polytechnic

• Coverage: Section 23-7 (Pages 468 – 474) of a textbook

Page 2: Objectives

• Understand basic comparator circuits

• Utilize hysteresis to mitigate noise influence

• Learning outcomes after completion of Part 4

Page 3: Functionality of Comparators

• Operational Amplifiers (Op-Amps) as Comparators:

  • Compare two voltage levels

  • Determine when an input exceeds a specific reference voltage

• Open-loop Configuration:

  • One input receives the voltage to be compared (Vin)

  • The other input receives a reference voltage

  • Implications of operating in open-loop configurations: High voltage gain

Page 4: Operational Amplifier in Open-loop Configuration

• Diagram illustrating the op-amp setup

  • Input voltages are V+ and V-

• Relationship: Vout = Aol * (V+ - V-)

• Use of supply voltages: +15V and -15V

Page 5: Types of Op-Amp Comparators

• Three Major Types:

  • Zero Level Comparator (or Detector)

  • Non-Zero Level Comparator

  • Comparator with Hysteresis

Page 6: Zero Level Comparator

• Very minimal voltage difference triggers the op-amp sweet into saturation

• Example calculation:

  • Aol = 100,000

  • Voltage difference = 0.25mV

  • Output voltage = 0.25mV * 100,000 = 25V

• Behavior of the op-amp under minimal input differences

Page 7: Predicting Output Voltage

• Comparison of V+ and V-:

  • If V+ > V- then Vout = +Vsat

  • If V- > V+ then Vout = -Vsat

• Importance of output switching based on input comparisons

Page 8: Non-Zero Level Comparator

• Operation based on defined reference voltage (Vref)

• Output Scenarios:

  • If V+ > V- : Vout = +Vo(sat)

  • If V- > V+ : Vout = -Vo(sat)

Page 9: Output Characteristics

• Time variation in output states consistent with input conditions

• Graphical representation showing transitions based on V+ and V- comparisons

Page 10: Reference to Example 23.6

• Introduction of Example 23.6 for practical illustration

• Relevant page references (23-32, 23-33)

Page 11: Effects of Input Noise

• Discussion on noise interference affecting input voltages

• Importance of managing noise in comparator operations

Page 12: Noise Impact on Comparison

• Illustration of output response amidst input noise fluctuations

• Conceptual understanding of noise peaks' effects on output

Page 13: Hysteresis in Comparators

• Concept of Hysteresis:

  • Very important for reducing sensitivity to noise

  • Higher reference during input rise (UTP) versus during fall (LTP)

Page 14: Positive Feedback Feedback Implementation

• Scenario discussion when output is at positive maximum (+Vo(sat))

  • Transitioning output based on input exceeding UTP

Page 15: Negative Output Transition

• Vout transitioning to the maximum negative voltage (-Vo(sat)) when input surpasses UTP

• Principles governing feedback voltage to non-inverting inputs

Page 16: Defining Trigger Points

• Identifying the UTP and LTP during transitions between output states

Page 17: Hysteresis Summary

• Positive feedback leads to a stable transition mechanism

• A comparator with hysteresis is often called a Schmitt trigger

  • Hysteresis is quantified by VHYS = VUTP - VLTP

Page 18: Example 23-7

• Problem-solving scenario concerning upper and lower trigger points

• Assumptions of given conditions (+Vsat = 8V, -Vsat = -8V)

Page 19: Summary of Key Concepts

• Overview of comparators operating in open-loop mode

• Functionality of zero-level and hysteresis-enabled comparators

Page 20: Basic Op-Amp Characteristics

• Properties of basic operational amplifiers

  • High open-loop voltage gain, high input impedance, low output impedance

• Voltage gain and input/output impedance equations

Page 21: Voltage-Follower and Inverting Amplifier

• Overview and equations relating to voltage follower and inverting amplifier configurations

Page 22: Visual Representation of Comparator Types

• Graphical depiction of zero-level detector, non-zero level detector, and hysteresis comparator

• Mathematical expressions for UTP and LTP using resistors in the circuit

Page 23: End of Chapter 23

• Closure of Chapter 23 with acknowledgments of copyright.