| 摘要 |
PURPOSE:To correct uniformly electrostatic charging and to stabilize picture quality by controlling a light emissin source electrically according to resolution and varying line width, and also varying the compensation characteristic of a decrease in electrostatic charging. CONSTITUTION:When an intensity specifying signal SD indicates that a high resolution mode is off, a transistor (TR) Q1 turns off and a modulated signal LEDS, on the other hand, is inputted to a modulating circuit 210 to drive a laser diode 12a with a driving current obtained by superposing the modulated signal upon a bias current ic. Namely, the potential is raised almost to a threshold value T with the bias current ic and the diode is driven with the current having the modulated signal LEDS superposed thereupon. The light emission state is monitored on a monitor diode 12b so as to hold the laser power constant and fed back through an amplifier 211 and a gain varying circuit 212, and a comparing circuit 213 compares the modulated signal LEDS with the feedback signal FS to control the bias current ic, controlling the laser power to a constant value. When the signal SD indicates that a low resolution state on, similar operation is performed. Thus, the uniform electrostatic charging correction is made to hold the picture quality constant. |
