General Description Of Ccd Control; Photo-Voltaic Conversion - Toshiba DP1600 Service Manual

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.
Transfer area
Photosensor area
Transfer area
Shift register
1600/2000/2500 SCANNER
1 2 3 4 7447 7448
Principle of CCD Photo-Voltaic Conversion
7 - 12
Transfer clock
Optical energy
7449 7450
Detailed photosensor
Transfer clock
December 2000 © TOSHIBA TEC
P-layer
N-layer
08-06-01