= Inverting low-pass amplifier
{title2=$G(\omega)=-R_f/[R_i(1+i\omega R_fC)]$}
An ideal <operational amplifier> with a grounded noninverting input, input <resistor> $R_i$, and parallel feedback <resistor> $R_f$ and <capacitor> $C$ implements a <low-pass filter>. The <virtual short> and <Kirchhoff's current law> give $V_{\rm out}/V_{\rm in}=-Z_f/R_i$, where $Z_f=R_f/(1+i\omega R_fC)$. The DC gain magnitude is $R_f/R_i$ and the <cutoff frequency> is $1/(2\pi R_fC)$. The <capacitance> reduces high-<frequency> feedback <electrical impedance>, causing the gain magnitude to fall.
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