Editing Current mirror (section)

==== Output resistance ====
If ''V''<sub>BC</sub> is greater than zero in output transistor Q<sub>2</sub>, the collector current in Q<sub>2</sub> will be somewhat larger than for Q<sub>1</sub> due to the [[Early effect]]. In other words, the mirror has a finite output (or Norton) resistance given by the ''r''<sub>o</sub> of the output transistor, namely:
: <math> R_N = r_o = \frac{V_A + V_{CE}}{I_C} \ ,</math>

where ''V''<sub>A</sub> is the Early voltage; and ''V''<sub>CE</sub>, the collector-to-emitter voltage of output transistor.