The minimum output voltage of the Wilson current mirror must exceed the base emitter voltage of Q2 by enough that Q3 will operate in active mode rather than saturation. Gilbert reports data on a representative implementation of a Wilson current mirror that showed constant output current for an output voltage as low as 880 millivolts. Since the circuit was biased for high frequency operation (formula_85), this represents a saturation voltage for Q3 of 0.1 to 0.2 volts. By contrast, the standard two-transistor mirror operates down to the saturation voltage of its output transistor.