LOW VOLTAGE LASER DRIVER

摘要

A laser driver circuit (fig. 2) includes a resistor Rnew above the load resistors R1 and R2 and a transistor M1, its drain connected to node Ni, driven by an adjustable analog control bleeder bias, the operation of the bleeder transistor M1 is as follows. As the bleeder bias voltage increases, the current ID also increase. ID is the same current that is going to ground from node N1. As ID increases, the voltage drop across Rnew increases, thereby the voltage at node Ni is decreased. The lower voltage at N1 results in lower voltages at Diff_n and Diff_p, which in turn lowers the voltages at the bases of Q10 and Q11. So through this chain of events the current through M1 adjusts the base voltages of Q10 and Q11. The laser driver can be easily used with different types of laser devices having different switch on voltages because the bleeder bias voltage can be easily changed so that base voltages of Q10 and Q11 fall below the collector voltages. Moreover, only one voltage supply of 3.3 V is needed.