The basic comparator configuration can produce a noisy "chatter" output if the applied differential input voltage is near the comparator's offset voltage. This usually occurs when the input signal is moving very slowly across the switching threshold of the comparator. This problem can be prevented by adding external hysteresis to the comparator.

External hysteresis can be applied in the form of a positive feedback loop that adjusts the trip point of the comparator depending on the current output state.

The hysteresis transfer curve is shown in Figure 7-2. This curve is a function of three components: V_TH, V_OS, and V_HYST:

• V_TH is the actual set voltage or threshold trip voltage.
• V_OS is the internal offset voltage between V_IN+ and V_IN–. This voltage is added to V_TH to form the actual trip point at which the comparator must respond to change output states.
• V_HYST is the hysteresis (or trip window) that is designed to reduce comparator sensitivity to noise.

Figure 7-2 Hysteresis Transfer Curve

For more information, please see Application Note SBOA219 "Comparator with and without hysteresis circuit".