Hysteresis

AN4071

16/27

Doc ID 022939 Rev 1

4

Hysteresis

For slow time changing input signal, an output oscillation can appear while the input signal

remains close to the reference voltage. Also low amplitude signal on high impedance can

cause oscillations due to noise background. Such unwelcome behavior can be solved by

hysteresis. The principle of hysteresis consists of two different input threshold voltages

depending on actual output state.

4.1

Built-in hysteresis

Many comparators have built-in hysteresis. Typical hysteresis value is a few mV. This is

enough to suppress output undesired toggling in most cases but it doesn't impact

significantly the resolution of the comparator. For comparators with built-in hysteresis, the

average lower and upper threshold voltage is computed and referred as input offset voltage

Figure 17.

Figure 17.

Trip point voltage definition

Figure 18.

Input hysteresis