| 摘要 |
PURPOSE:To prevent the saturation of a generated signal and blooming, by using a maximum value of the photodetecting amount of a light sensor of a picture scanner to control a frequency of a transfer clock and to operate the light sensor within a dynamic range. CONSTITUTION:The maximum value of the photodetecting amount of the light sensor of a CCD 12 is detected at a peak hold circuit and held for one scanning period. The value is compared with a reference voltage 14 corresponding to a saturated voltage of the light sensor at a differential amplifier 15. When the peak value approaches the saturated voltage, a differential output voltage is low, and a voltage controlled oscillator (VCO) 16 generates a high frequency. Since the output of the VCO controls the transfer time to the CCD 12, the CCD is not saturated and operated within the dynamic range. Even if a light strong is made incident locally to the CCD 12, the saturation of electric charges and the diffusion of excessive charge are prevented. |
