Sbu (Sensor Board Unit) - Ricoh Aficio MP2550B Service Manual

6.5.2 SBU (SENSOR BOARD UNIT)

Monochrome Scanner Unit
The CCD converts the light reflected from the original into an analog signal. The CCD line
has 7,400 pixels and the resolution is 600 dpi (23.6 lines/mm).
The CCD has two output lines, for odd and even pixels, to the analog processing IC. The
analog processing IC performs the following operations on the signals from the CCD:
1. Z/C (Zero Clamp):
Adjusts the black level reference for even pixels to match the odd pixels.
2. Signal Amplification:
The analog signal is amplified by operational amplifiers in the AGC circuit.
3. Auto Gain Control
Adjusts the gain curve for the scanned image density.
After the above processing, the analog signals are converted to 8-bit signals by the A/D
converter. This will give a value for each pixel on a scale of 256 grades. Then, the digitized
image data goes to the IPU board.
SM 6-23
Image Processing
D017/D018/D019/D020