Epson PhotoPC 800 Service Manual page 37

EPSON PhotoPC 800
2.2.1.3 IC902 (H Driver) and IC904 (V Driver)
An H driver (IC902) and V driver (IC904) are necessary in order to generate the
clocks (vertical transfer clock, horizontal transfer clock and electronic shutter
clock) which driver the CCD. IC902 is an inverter IC which drives the horizontal
CCDs (H1 and H2). In addition the XV1-XV4 signals which are output from
IC102 are the vertical transfer clocks, and the XSG1 and XSG signal which is
output from IC102 is superimposed onto XV1 and XV3 at IC904 in order to
generate a ternary pulse. In addition, the XSUB signal which is output from
IC102 is used as the sweep pulse for the electronic shutter, and the RG signal
which is output from IC102 is the reset gate clock.
Figure 2-6. IC902 Block Diagram
Figure 2-7. IC904 Block Diagram
Operating Principle
2.2.1.4 IC905 (CDS, AGC Circuit, A/D Converter)
The video signal which is output from the CCD is input to Pins (26) and (27) of
IC905. There are S/H blocks inside IC905 generated from the XSHP and
XSHD pulse, and it is here that CDS (correlated double sampling) is carried
out. After passing through the CDS circuit, the signal passes through the AGC
amplifier. It is A/C converted internally into a 10-bit signal, and is then input to
IC102 of the CA2 circuit board. The gain of the AGC amplifier is controlled by
the serial communication from IC102 of the CA2 circuit board.
Operating principles of the Circuit Boards
Figure 2-8. IC905 Block Diagram
Revision A
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