Sbu (Sensor Board Unit) - Gestetner A193 Service Manual

IMAGE PROCESSING

2.2 SBU (SENSOR BOARD UNIT)

A m p .
O D D
E V E N
Z/C: Zero Clamp
AGC: Automatic Gain Control Circuit
The CCD converts the light reflected from the original into an analog signal.
The CCD line contains 5,000 pixels and the resolution is 400 dpi (15.7
lines/mm).
The CCD has two output lines, for odd and even pixels, which are sent 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 numbered pixels to match black
level of the numbered odd pixels.
2) Signal Composition:
Analog signals for odd and even pixels from the CCD are merged by a
switching device.
3) Signal Amplification
The analog signal is amplified by operational amplifiers in the AGC circuit.
The maximum gains of the operational amplifiers are controlled by the
CPU on the BICU board.
After the above processing, the analog signals are converted into 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 will be sent to the BICU board.
(A193)
Z/C
Z/C
A G C
Reference
Controller
Analog
Processing IC
SBU: Sensor Board Unit
BICU: Base Engine & Image Processing Control
A/D: Analog/Digital Converter
2-6
SBU BICU
IPU
A/D
Vin
ref
A193D502.wmf
SM