Loaded Node Feeds Sample - Electronic Circuits V & VI: Front-End Conditioning and Op-Amp Feedback Step by Step

This loaded-node-feeds-sample lesson makes the sampler capture the node voltage that remains after the source resistance and input load divide the source. The 12 V source with 3 ohm internal resistance and 9 ohm input load gives a 9 V held sample only for the stated ideal divider and closed-switch row. Real front ends add source impedance variation, sampling capacitance, switch resistance, leakage, settling time, noise, finite precision, and measurement uncertainty.

A front-end sampler captures the node voltage left after the source is loaded. 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 input load sets the node voltage

A 12 volt source with 3 ohms inside and 9 ohms at the input gives 9 volts at the node.

12\ \text{V}/(3\ \text{ohm}+9\ \text{ohm}) = 1\ \text{A}

The sampler captures the loaded node

With the sample switch closed, the held voltage is the loaded 9 volt node.

V_{\text{held}} = V_{\text{in}} = 9\ \text{V}