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A non-inverting operational amplifier applies the signal to its non-inverting input and returns part of the output to its inverting input through negative feedback. Connect resistor $R_f$ from the output to the inverting input, and resistor $R_g$ from that input to a reference circuit node at electric potential $V_{\mathrm{ref}}$.

In stable, unsaturated ideal operation, the inputs draw no electric current and their electric potentials are equal. Writing the signal as $V_{\mathrm{in}}$, Kirchhoff's current law at the inverting input givessoFor a grounded reference circuit node, the voltage gain is $1+R_f/R_g$. For example, $R_f=20\mathrm{k\Omega }$ and $R_g=10\mathrm{k\Omega }$ give gain three. The equal-input-potential approximation requires sufficiently large loop gain; amplifier saturation or unstable feedback invalidates it.^[ref]