What does the term "hysteresis" refer to in the context of a Schmitt trigger?

The term "hysteresis" in the context of a Schmitt trigger refers to the difference between the input voltage levels required to switch the output from one state to another (e.g., from low to high or high to low). This characteristic is essential because it creates two distinct thresholds: an upper threshold voltage and a lower threshold voltage. When the input voltage exceeds the upper threshold, the output changes to one state, and when it falls below the lower threshold, it changes back to the opposite state.

This behavior prevents rapid oscillations in the output when the input signal is noisy or slowly varying, thereby providing a more stable and reliable output. It is particularly useful in applications where clean digital signals are required from potentially noisy analog inputs. The presence of hysteresis ensures that once a transition occurs, it is not easily reversed until the input voltage significantly changes, effectively creating a buffer against minor fluctuations around the switching threshold.