Toshiba e-studio 250 - General Description of CCD Control; Photo-Voltaic Conversion

e-STUDIO160/200/250 SCANNER 7 - 12 December 2002 TOSHIBA TEC
7.6 General Description of CCD control
7.6.1 Photo-voltaic conversion
The purpose of photo-voltaic conversion is to form electrical signals corresponding to the intensity of light
reflected from the original. A CCD (Charge Coupled Device) is used for photo-voltaic conversion. CCDs
are single-chip photo-voltaic conversion device in which several thousands of photosensing elements
several microns square are arranged in a single line. This copier uses a CCD having 7,450 of these
photosensing elements.
The photosensor comprises a P-layer, N-layer semiconductor. Optical energy generates a (-) (minus)
charge on the P-layer proportional to the optical energy and irradiation time. The charge generated at the
photosensor is transferred to the transfer area, shifted from right to left in the figure below according to the
transfer clock, and is output from the CCD. During this operation, the reaction speed of the CCD is slow (it
takes time for the charge to be transferred by the shift register), so even-numbered and odd-numbered
image signals are output in parallel.
1 2 3 4 7447 7448 7449 7450
Transfer area
Transfer area
Photosensor area
Transfer clock
Optical energy
Detailed photosensor
P-layer
N-layer
Transfer clockShift register
08-06-01
Principle of CCD Photo-Voltaic Conversion