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.