Epson PhotoPC 800 Service Manual page 38

EPSON PhotoPC 800
2.2.1.5 Transfer of Electric Charge by the Horizontal CCD
The transfer system for the horizontal CCD emplays a 2-phase drive method.
The electric charges sent to the final stage of the horizontal CCD are
transferred to the floating diffusion, as shown in the figure below. RG is turned
on by the timing in (1), and the floating diffusion is charged to the potential of
PD. The RG is turned off by the timing in (2). In this condition, the floating
diffusion is floated at high impedance. The H1 potential becomes shallow by
the timing in (3), and the electric charges now moves to the floating diffusion.
Here, the electric charges are converted into voltage at the rate of V=Q/C by
the equivalent capacitance C of the floating diffusion. RG is then turned on
again by the timing in (1) when the H1 potential becomes deep. Thus, the
potential of the floating diffusion charges in proportion to the quality of
transferred electric charge, and becomes CCD output after being received by
the source follower. The equivalent circuit for the output circuit is shown in
figure2-10.
Floating diffusion
Figure 2-9. Horizontal Transfer if CCD Imager and Extraction of
Signal Voltage
Operating Principle
RG pulse peak si
Black leve
Signal volta
Operating principles of the Circuit Boards
Reset gate pulse
Direction of transfer
H Register
Electric charge
Floating diffusion gate is
floated at a high impedance.
C is charged
equivalently
Figure 2-10. Theory of Signal Extraction Operation
Revision A
13V Pre-charge drain bia
Voltage output
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