Editing Low-noise amplifier (section)

=== Impedance ===
The circuit topology affects input and output impedance. In general, the source impedance is matched to the input impedance because that will maximize the power transfer from the source to the device. If the source impedance is low, then a [[common base]] or [[common gate]] circuit topology may be appropriate. For a medium source impedance, a [[common emitter]] or [[common source]] [[Topology (electrical circuits)|topology]] may be used. With a high source resistance, a [[common collector]] or [[common drain]] topology may be appropriate. An input [[impedance match]] may not produce the lowest noise figure. <!--There is another notion of a noise impedance match. Need a description of noise models. -->