LIGHT EMITTING ELEMENT DRIVE CIRCUIT

摘要

PROBLEM TO BE SOLVED: To provide a stable luminous intensity even if 'low' codes have been continued in a laser diode(LD) drive circuit of a light transmitter for optical digital transmission system. SOLUTION: In this LD drive circuit output light from a laser diode (1) is monitored (2), this monitor output is subjected to current/voltage conversion (4) and its level is detected (5). After applying a luminous intensity setting voltage so as to obtain a prescribed output light at the voltage level, input data are sampled and held by a sample-and-hold circuit (6), the result is fed back to a laser diode drive current circuit (3) so as to prevent reduction in a laser diode drive current due to consecution of low level of input data. Furthermore, a discharge resistor is connected in parallel with a hold capacitor in a peak detection circuit and effect of a malfunction due to noise is reduced by optimizing the time constant.