Switch Samples Input - Electronic Circuits V & VI: Front-End Conditioning and Op-Amp Feedback Step by Step

A closed sample switch lets the storage node copy the input voltage, so the held value begins as a captured snapshot. The 4 V result is exact for an ideal switch and capacitor after settling; real sample-and-hold circuits include switch resistance, acquisition time, charge injection, capacitor tolerance, droop, and measurement uncertainty.

A closed sample switch copies the input to the held node in this final-state model. 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 closed switch copies the input

With the sample switch closed, the input of 4 volts becomes the held value.

V_{\text{held}} = V_{\text{in}} = 4\ \text{V}

The capacitor stores the held voltage

The capacitance is shown as 2 farads, but this lesson claims only the final held voltage.

C = 2\ \text{F}\qquad V_{\text{held}} = 4\ \text{V}