Inverter From Switches - Electronic Circuits IV: Digital Logic Signals and Switch Networks Step by Step

A pull-up plus controlled pull-down turns a HIGH input into a LOW output and a LOW input into a HIGH output. Exact arithmetic here means exact results for the stated model inputs; measured inputs still carry uncertainty and significant-figure limits.

highlighted = computed this step

LOW input leaves the pull-down open

With input 0 volts, the switch is open and the output is 5 volts.

\text{LOW in} \Rightarrow V_{\text{out}} = 5\ \text{V}

HIGH input closes the pull-down

With input 5 volts, the pull-down path closes and the output becomes 0 volts.

\text{HIGH in} \Rightarrow V_{\text{out}} = 0\ \text{V}