Abstract: A circuit source has bias and modulation current generators for both p-type and n-type optical sources, and a pair of sources of control voltages for the bias and modulation current generators, which obtain pairs of control voltages from an adjustable driving current. An external signal allows selecting, by means of a control logic and CMOS gates, the generators required by the source. The circuit is made by using three pads of an integrated circuit, one for each control voltage source and the third comprising the current generators, the CMOS gates and the control logic.