Ricoh PRIPORT VT 2000 Series Service Manual page 46

28 February '91
2). DC Clamping
The OS signal is amplified by Q607. The dc clamping switch is turned
ON/OFF by the DCREST signal. The switch turns on when the CCD
produces black level (empty data) at the end of scanning and is off during
image scanning.
When the switch turns on, the black level signal is stored in capacitor C669.
When the switch turns off, the black level signal is input to IC624 pin 3
while the image signal is input to the IC624 pin 2.
The difference between the image signal and the black level signal is
amplified and output from the IC624.
This output signal from IC624 is amplified again in IC620. The signal then
goes in the A/D converter.
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