AUTOMATIC POWER CONTROL METHOD FOR OPTICAL TRANSMISSION CIRCUIT AND AUTOMATIC POWER CONTROL CIRCUIT FOR OPTICAL TRANSMISSION CIRCUIT

摘要

PURPOSE:To make an output power and a duty ratio constant by detecting a mean value of input data and a peak level and a mean value of a signal resulting from electric-conversion at a light receiving diode and controlling a bias current and a pulse current based on this. CONSTITUTION:A control circuit 6 gives the terminal voltage of a resistor 14 as a reference voltage when a front output power of a laser diode 12 is a regular power. The circuit 6 controls a bias circuit(2) 8 so that the output voltage of a peak value detection circuit 4 is equal to a reference voltage to decide a bias current. Thus, the output of the diode 12 is controlled to have regular power. Then a mean value outputted from a mean value detection circuit(1) 3 and a mean value outputted from a mean value detection circuit(2) 5 are compared to control a bias current and a pulse current while keeping the optical output power constant. In this case, the pulse current is increased by the decreased bias current. This is implemented till the mean value of the circuit(2) 5 and the mean value of the circuit(1) 3 have a predetermined relation. Thus, the duty ratio is controlled to be 50% equal to the regular power.