Comparator Hysteresis Calculator

Calculator Input

Topology Non-Inverting Inverting

High output level V_OH (V)

Low output level V_OL (V)

Reference voltage V_REF (V)

Feedback resistor R_F (Ω)

Reference resistor R_REF (Ω)

Graph minimum input (V)

Graph maximum input (V)

Graph points

Calculate Hysteresis

Plotly Graph

The graph compares rising and falling input sweeps against the output state. It helps you see the switching gap created by hysteresis.

Example Data Table

Formula Used

This calculator assumes a resistor from the output to the threshold node and another resistor from the reference source to the same node.

Threshold node voltage:

V_TH = (V_OUT × R_REF + V_REF × R_F) / (R_F + R_REF)

Threshold when output is high:

V_TH,H = (V_OH × R_REF + V_REF × R_F) / (R_F + R_REF)

Threshold when output is low:

V_TH,L = (V_OL × R_REF + V_REF × R_F) / (R_F + R_REF)

Hysteresis width:

ΔV_HYS = |V_TH,H - V_TH,L|

Center voltage:

V_CENTER = (V_TH,H + V_TH,L) / 2

Feedback factor:

β = R_REF / (R_F + R_REF)

How to Use This Calculator

1. Select the comparator topology. Choose non-inverting or inverting.
2. Enter the expected high and low output levels of your comparator.
3. Enter the reference voltage tied to the threshold network.
4. Enter the resistor from output to threshold node as R_F.
5. Enter the resistor from reference source to threshold node as R_REF.
6. Set graph limits to cover the input range you want to inspect.
7. Press the calculate button.
8. Review the result block above the form for trip points, width, and center voltage.
9. Download the output as CSV or PDF if needed.
10. Use the graph to compare rising and falling switching paths.

Comparator Hysteresis Overview

Why hysteresis matters

Comparator hysteresis creates two switching levels instead of one. That small gap stops rapid toggling near the decision point. It is useful when the input contains noise, ripple, or slow edges. A clean transition improves stability and repeatability.

How the resistor network works

The output is fed back to the threshold node through a resistor. A second resistor ties that same node to a reference voltage. When the output changes state, the threshold node also moves. This movement shifts the next switching point. That is the core idea behind hysteresis.

What this calculator returns

This page calculates the threshold with a high output state and the threshold with a low output state. It also gives the upper threshold, lower threshold, hysteresis width, center voltage, and half-band value. These values help you compare sensitivity against noise tolerance.

How topology changes interpretation

The same threshold values can be mapped differently in inverting and non-inverting designs. In a non-inverting design, the rising input trip usually matches the low-state threshold. The falling input trip usually matches the high-state threshold. In an inverting design, the mapping reverses. This tool handles that interpretation automatically.

How to tune the design

If you increase the reference-side resistor share, the feedback factor grows. That makes the threshold shift larger when the output changes. A larger shift means more hysteresis width. More width improves noise immunity, but it also demands a larger input change before the next transition happens.

Using the graph and exports

The graph shows rising and falling input sweeps. This makes the switching gap easy to inspect. The export buttons let you save the current design result as CSV or PDF. That is helpful for reviews, lab notes, and design comparisons.

FAQs

1. What is comparator hysteresis?

Comparator hysteresis is the voltage gap between two switching thresholds. One threshold is used for a rising input, and the other is used for a falling input. The gap reduces false switching caused by noise.

2. Why do designers add hysteresis?

Designers add hysteresis to stop chatter near the decision point. It improves switching stability when the input signal moves slowly or contains noise, ripple, or interference.

3. How do resistor values affect hysteresis width?

The resistor ratio controls how much output voltage is fed back to the threshold node. More feedback produces a larger threshold shift and therefore a wider hysteresis band.

4. Does the reference voltage change both thresholds?

Yes. The reference voltage shifts the threshold band up or down. It changes the center point, while the resistor ratio and output swing mainly set the band width.

5. Can I use negative output rails?

Yes. The calculator accepts positive or negative output levels. That makes it useful for bipolar designs, level-shifted systems, and mixed-signal threshold checks.

6. Why are rising and falling trip points different?

They differ because the output state changes the feedback voltage. Once the comparator flips, the threshold moves, so the next trip point occurs at a different input level.

7. Is hysteresis width the same as noise margin?

Not exactly. Hysteresis width shows the full separation between thresholds. Designers often use half of that width as a quick estimate of the disturbance level the input can absorb around the center region.

8. Which topology should I choose?

Use the topology that matches your actual signal path. Non-inverting mode is common when the signal enters the positive input. Inverting mode is common when the signal enters the negative input.