Understanding Electrical Comparators and Their Types

Aug 7, 2024

Notes on Comparators

Introduction

  • Topic: Comparators in electrical and electronic circuits.
  • Purpose: Compare two voltage levels for practical applications (e.g., temperature measurement).

Functionality of Comparators

  • Inputs: Two inputs - Inverting and Non-Inverting.
  • Output: Digital output (High or Low).
    • High Output: When Non-Inverting input > Inverting input.
    • Low Output: When Inverting input > Non-Inverting input.
  • Acts as a 1-bit analog to digital converter.
    • Commonly used in Analog to Digital conversions.

Schematic and Operation

  • Schematic similar to Op-Amp, with two inputs and one output (open loop condition).
  • **Op-Amp in Open Loop: **
    • Output = Open loop gain x Differential input voltage.
    • High output if Non-Inverting input is greater; otherwise, low output.

Advantages of Comparator ICs over Op-Amps

  • Comparator ICs designed specifically for fast applications:
    • Minimum propagation delay.
    • Faster rise and fall times (higher slew rate).
  • Open collector output stage allows for:
    • External pull-up resistor usage.
    • Compatibility with different logic families and wired AND configurations.
  • Op-Amps can have limitations in output compatibility.

Types of Comparators

  • Inverting Comparator:
    • Input applied to the Inverting terminal.
    • Output goes LOW when input > reference voltage.
  • Non-Inverting Comparator:
    • Input applied to the Non-Inverting terminal.
    • Output goes HIGH when input > reference voltage.

Example of Comparator Behavior

  • Non-Inverting Comparator Example:
    • Triangular wave input compared to a reference voltage.
    • Output HIGH only when input > reference voltage.
  • Inverting Comparator:
    • Output LOW when input > reference voltage.

Window Comparator

  • Designed to output HIGH only when input voltage is between two thresholds (lower and upper).
  • Comprised of:
    • Inverting and Non-Inverting comparators combined with pull-up resistors.
  • Behavior:
    • Output HIGH when input is within specified band of voltages (VL < input < VH).

Noise Immunity and Hysteresis

  • Comparators may not handle noise effectively.
  • Noise can cause fluctuations in output signals.
  • Solution: Implementing Hysteresis (Schmitt Trigger circuits).
    • Positive feedback increases noise immunity.

Conclusion

  • Overview of comparators and their applications in voltage comparison.
  • Introduction to Schmitt Trigger circuits for improved performance against noise.