Without hysteresis a comparator oscillates rapidly when the input hovers near the threshold due to noise.

How much hysteresis do I need?

The hysteresis band should be wider than the expected noise on the input signal.

Is this the same as a Schmitt trigger?

Yes, a comparator with hysteresis is functionally a Schmitt trigger.

Comparator Hysteresis Calculator

Calculate the upper and lower trip points for a comparator with positive feedback hysteresis.

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Reference Voltage

Output High Voltage

R1 (to output)

kΩ

R2 (to reference)

kΩ

Upper Trip Point

2.727 V

Lower Trip Point2.273 V

Hysteresis Band0.455 V

Upper Trip Point vs Reference Voltage

View formula & how it works →

Comparator Hysteresis

Positive feedback adds hysteresis to prevent output chatter on noisy signals.

Formulas

V_upper = V_ref + (V_out_high - V_ref) x R2 / (R1 + R2)

V_lower = V_ref - V_ref x R2 / (R1 + R2)

Hysteresis = V_out_high x R2 / (R1 + R2)

Example Calculation

Vref = 2.5 V, output swings to 5 V, R1 = 100k, R2 = 10k.

01Upper = 2.5 + (5 - 2.5) x 10/110 = 2.5 + 0.227 = 2.727 V
02Lower = 2.5 - 2.5 x 10/110 = 2.5 - 0.227 = 2.273 V
03Hysteresis = 5 x 10/110 = 0.455 V

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