| 摘要 |
PURPOSE:To obtain stable gradation reproducibility by providing a constant current source provided apart from a semiconductor laser driving current source, and a high speed switching element controlling whether or not the constant current from the constant current source is added to the drive current from the semiconductor laser driving current source. CONSTITUTION:A current amplifying part 7 inputs the voltage held to an S/H part 6 and amplifies a reference current corresponding to a voltage value to output the same. The reference current outputted from the current amplifying part 7 is added to or not added to the constant currents from the first and second constant current sources 11, 12 to be inputted to a laser drive part 8. Whether or not the constant currents from the constant sources 11, 12 are added to the reference current outputted from the current amplifying part 7 to be inputted to the laser drive part 8 is changed corresponding to the values of the first and second bits of the intensity modulation control signal inputted to a quantity-of-light setting part 3. By this method, it is controlled whether or not the constant currents from the constant current sources are to be added to the drive current from a semiconductor laser driving current source to make it possible to obtain the high speed followability to the video signal of laser output. |
