Designing Comparator Circuits with 2 Different Thresholds

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Discussion Overview

The discussion revolves around designing a comparator circuit that can operate with two different switching thresholds. Participants explore various methods to achieve this, including the use of hysteresis and feedback networks, while addressing the challenges encountered in the design process.

Discussion Character

  • Technical explanation, Debate/contested

Main Points Raised

  • One participant describes a design requirement for a comparator with two sets of thresholds (3V/1V and 8V/3V) and mentions difficulties in achieving distinct switching levels through reference voltage adjustments.
  • The same participant discusses the implementation of a T network in the hysteresis feedback but expresses uncertainty about the mathematical aspects of this network.
  • Another participant suggests using three comparators for each threshold reference level and implementing hysteresis through a digital logic finite state machine to simplify the design and eliminate variability.
  • A request is made for a circuit diagram to better understand the proposed design.
  • A participant references a figure from an external source that resembles their circuit, noting a modification involving a T-network replacing a feedback resistor.

Areas of Agreement / Disagreement

Participants present differing approaches to the problem, with no consensus on the best method for achieving the desired comparator functionality. The discussion remains unresolved regarding the effectiveness of the proposed solutions.

Contextual Notes

Participants express uncertainty about the mathematical modeling of the T network and the implications of using digital logic for hysteresis, indicating potential limitations in their current understanding or design approach.

likephysics
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I am trying to design a comparator which is required to have 2 different switching thresholds.

The comparator +ve input is connected to a signal source (triangle wave). The -ve is connected to a reference voltage.

The first threshold will be say Vth+ = 3V and Vth- = 1V
and second threshold Vth+ = 8V and Vth-= 3V

I tried changing the reference voltage. But both levels either go up or down.
I added a T network in the hysteresis feedback network. The grounded resistor in t network would be open for the first set of threshold and it would be grounded for the second set. It helps a bit. I can't figure out the math of t network.

Any other ideas?
 
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The easiest way is to allocate 3 comparators at each threshold reference level and do the hysteresis in a digital logic finite state-machine. That eliminates the variability and complexity of feedback loops and delays.
 
Can you show us your circuit?
 

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