| 摘要 |
PURPOSE:To provide a light transmission circuit with a low power consumption which maintains the output average value and the degree of light modulation of light signal regardless of the temperature fluctuation of an LD diode. CONSTITUTION:A photo diode 2, an average value detection circuit 7, a voltage comparison circuit 6, and an LD bias current drive circuit 5 control the bias current of a laser diode (LD) 1, thus automatically controlling the output level of light signal. A memory 9 stores the input level data of analog signal to the LD 1 generating a light signal with the same degree of light modulation regardless of change in temperature near the LD 1. A temperature sensor 3 detects the temperature near the LD 1 and an A/D 10 generates a temperature close to the digital detection temperature. The memory 9 supplies an input level data corresponding to the detection nearby temperature to a D/A 8, the D/A 8 controls a variable gain amplification circuit 4 according to an analog input level data, and an analog signal at a level maintaining the degree of light modulation to be constant at any nearby temperature is set to the output of the amplification circuit 4. |
