Stiffness Changes Decision - Electronic Circuits V & VI: Front-End Conditioning and Op-Amp Feedback Step by Step

This stiffness-changes-decision lesson shows that changing source resistance can move the loaded input across later threshold bands. The 4 V weak-source LOW row and 8 V stiff-source HIGH row are exact only for the stated ideal loading and threshold model. Real decisions depend on input bias, source impedance, noise, hysteresis, bandwidth, settling time, finite precision, and measurement uncertainty.

Changing source resistance changes the voltage that reaches the decision stage. 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 weak source falls below the decision band

The weak source leaves only 4 volts at the input, below the lower threshold of 5 volts.

4\ \text{V} \le 5\ \text{V}\Rightarrow \text{LOW}

The stiff source crosses the upper threshold

The stiff source leaves 8 volts at the input, above the upper threshold of 6 volts.

8\ \text{V} \ge 6\ \text{V}\Rightarrow \text{HIGH}