Strict Threshold Three-Row Scan - Electronic Circuits II & III: Decision Networks and Interfaces Step by Step

A strict-threshold scan separates the measured node voltage from the decision rule, so equality stays low and only values above the threshold switch high. The table is exact only for the declared voltage and threshold values plus an ideal noiseless comparator; real decisions are shaped by offset, hysteresis, input bias, noise, finite transition time, threshold drift, source impedance, temperature, and voltage measurement uncertainty.

Below, equal, and above threshold produce different ideal switch decisions. 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 threshold rule is strict

The ideal switch closes only when the measured voltage is above the threshold. Equal to the threshold is not above it.

\text{closed only if }V_m>V_{\text{threshold}}

Below, equal, and above are different rows

The measured value changes while the threshold stays fixed. The decision column is derived from the strict comparison.

\begin{array}{c|c|c}V_m&V_{\text{threshold}}&\text{decision}\\0\ \text{V}&1\ \text{V}&LOW\\1\ \text{V}&1\ \text{V}&LOW\\2\ \text{V}&1\ \text{V}&HIGH\\\end{array}

Equal is still low for a strict above-threshold gate

For the rendered row, measured voltage and threshold are both 1 volt, so the ideal switch stays open.

1\ \text{V}=1\ \text{V}\Rightarrow \text{LOW}