DRIVER CIRCUIT FOR DRIVING A LIGHT EMITTING ELEMENT BY SUPERIMPOSING AN ANALOG SUB-INFORMATION SIGNAL OVER A DIGITAL MAIN SIGNAL

摘要

The present invention relates to a light emitting element driver circuit (2) which drives a light emitting element (1) by superimposing an analog sub-information signal over a digital main signal, thereby permitting the analog sub-information signal to be transmitted as an optical signal even if the digital main signal is intercepted. The light emitting element driver circuit (2) comprises the light emitting element (1); driver means for driving the light emitting element by superimposing, over a digital main signal including a bit sequence of "1" and "0", an analog sub-information signal whose frequency is lower than the bit rate of the digital main signal; input interception detector means (5) for detecting any interception of the inputting of the digital main signal; and gain-controlled amplifier means (7) responsive to said input interception for making the amplitude of the analog sub-information signal greater than before the interception of the digital main signal inputting.