Hysteresis and Margins

Rising Threshold Switches High

the upper boundary changes state

A Schmitt input uses the upper threshold to leave a prior LOW state. Exact arithmetic here means exact results for the stated model inputs; measured inputs still carry uncertainty and significant-figure limits.

highlighted = computed this step

The prior state is LOW before crossing

The input starts from a LOW history. The upper threshold is 3 volts.

Vupper=3 VV_{\text{upper}} = 3\ \text{V}
Rising thresholdThe Schmitt rule has a prior LOW state.V4 VV2 VV3 VV5 V+-4 V+-2 V+-3 V+-5 Vprior LOWHIGH

Crossing the upper threshold switches HIGH

The input is 4 volts, above the upper threshold, so the output becomes HIGH.

4 V≥3 V⇒HIGH4\ \text{V} \ge 3\ \text{V}\Rightarrow \text{HIGH}
Rising outputThe upper threshold makes the output HIGH.V4 VV2 VV3 VV5 V+-4 V+-2 V+-3 V+-5 Vprior LOWHIGH