Editing Buffer amplifier (section)

==Current buffer examples==
Simple unity gain buffer amplifiers include the [[bipolar junction transistor]] in [[common base|common-base]] configuration, or the [[MOSFET]] in [[common gate|common-gate]] configuration (called a ''current follower'' because the output current follows the input current). The current gain of a current buffer amplifier is (approximately) unity.

=== Simple transistor circuits ===
[[Image:Bipolar current follower2.PNG|thumbnail|200px|Figure 6: Bipolar current follower biased by current source ''I<sub>E</sub>'' and with active load ''I<sub>C</sub>'']]
Figure 6 shows a bipolar current buffer biased with a current source (designated ''I<sub>E</sub>'' for DC emitter current) and driving another DC current source as active load (designated ''I<sub>C</sub>'' for DC collector current). The AC input signal current ''i<sub>in</sub>'' is applied to the emitter node of the transistor by an AC [[Norton's theorem|Norton current source]] with Norton resistance ''R<sub>S</sub>''. The AC output current ''i<sub>out</sub>'' is delivered by the buffer via a large coupling capacitor to load ''R<sub>L</sub>''. This coupling capacitor is large enough to be a short circuit at frequencies of interest.

Because the transistor output resistance connects input and output sides of the circuit, there is a (very small) backward voltage feedback from the output to the input so this circuit is not unilateral. In addition, for the same reason, the input resistance depends (slightly) upon the output load resistance, and the output resistance depends significantly on the input driver resistance. For more detail see the article on [[common base|common base amplifier]].