Input impedance
= Input impedance
{title2=$Z_{\mathrm{in}}$}
<Input impedance> is the ratio of a small applied input-voltage <phasor> to the resulting input-current <phasor>, with the output termination and operating point specified. A finite <input impedance> loads a voltage source. For an <ideal operational amplifier> the <input impedance> is infinite, so neither input terminal draws current.