Editing Current mirror (section)

==== Compliance voltage ====
For Figure 3, a large op amp gain achieves the maximum ''R''<sub>out</sub> with only a small ''R''<sub>E</sub>. A low value for ''R''<sub>E</sub> means ''V''<sub>2</sub> also is small, allowing a low compliance voltage for this mirror, only a voltage ''V''<sub>2</sub> larger than the compliance voltage of the simple bipolar mirror. For this reason this type of mirror also is called a ''wide-swing current mirror'', because it allows the output voltage to swing low compared to other types of mirror that achieve a large ''R''<sub>out</sub> only at the expense of large compliance voltages.

With the MOSFET circuit of Figure 4, like the circuit in Figure 3, the larger the op amp gain ''A''<sub>v</sub>, the smaller ''R''<sub>E</sub> can be made at a given ''R''<sub>out</sub>, and the lower the compliance voltage of the mirror.