= Inverting operational amplifier
{title2=$V_o/V_i=-R_f/R_{\rm in}$}
Connect a <resistor> $R_{\rm in}$ from the input source to the inverting input, a feedback <resistor> $R_f$ from output to that same input, and ground the non-inverting input. For ideal linear operation the inverting node is a <virtual ground>. <Kirchhoff's current law> gives $V_i/R_{\rm in}+V_o/R_f=0$, yielding the displayed voltage gain. The source sees <input impedance> $R_{\rm in}$, even though the amplifier input itself has infinite <input impedance>.
Back to article page
