KLI−4104
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4
Notice that each chroma pixel covers 4 times the area of
a single luma pixel. An advantage to having larger pixel
sizes is increased responsivity. This is especially useful in
the chroma channels where some light is absorbed by the
color filter material. Please refer to Figure 12: Typical
Responsivity for the responsivity data.
Image Processing
By utilizing the data from all 4 channels, a high-resolution
color scan can be achieved. The luminance channel can be
used to provide the edge detail in the image.
Chroma Imaging
During the integration period, an image is obtained by
gathering electrons generated by photons incident upon the
photodiodes. The charge collected in the photodiode array
is a linear function of the local exposure. The charge is stored
in the photodiode itself and is isolated from the CCD shift
registers during the integration period by the transfer gates
TG1 and TG2, which are held at barrier potentials. At the
end of the integration period, the CCD register clocking is
stopped with the f1 and f2 gates being held in a ‘high’ and
‘low’ state respectively. Next, the TG gates are turned ‘on’
causing the charge to drain from the photodiode into the TG1
storage region. As TG1 is turned back ‘off’ charge is
transferred through TG2 and into the f1 storage region.
The TG2 gate is then turned ‘off’, isolating the shift registers
from the accumulation region once again. Complementary
clocking of the f1 and f2 phases now resumes for readout
of the current line of data while the next line of data is
integrated.
Luma Imaging
During the integration period, an image is obtained by
gathering electrons generated by photons incident upon the
photodiodes. The charge collected in the photodiode array
is a linear function of the local exposure. The charge is stored
in the photodiode and an accumulation region adjacent to the
photodiode. This transfer occurs with the bias applied to
TG1L. The accumulation storage region is isolated from t h e
CCD shift registers during the integration period by the
transfer gate TG2, which is held at barrier potentials. At the
end of the integration period, the CCD register clocking is
stopped with the f1Lx and f2Lx gates (x = A or B) being
held in a ‘high’ and ‘low’ state respectively. Next, the TG2
gate is turned ‘on’ causing the charge to drain from the
accumulation region into f1 storage region. The TG2 gate
is then turned ‘off’, isolating the shift registers from the
accumulation region once again. Complementary clocking
of the f1 and f2 phases now resumes for readout of the
current line of data while the next line of data is integrated.
Charge Transport and Sensing
In either the chroma or luma cases, readout of the signal
charge is accomplished by two-phase, complementary
clocking of the f1 and f2 gates, (labeled f1Cx/f2Cx or
f1Lx/f2Lx, where x = A or B). The register architecture has
been designed for high speed clocking with minimal
transport and output signal degradation, while still
maintaining low (7.25 Vp-p min) clock swings for reduced
power dissipation at 30 MHz thereby, lowering clock noise
and simplifying the driver design. The data in all registers is
clocked simultaneously toward the output structures.
The signal is then transferred to the output structures in
a parallel format at the falling edge of the H2 clocks.
Re-settable floating diffusions are used for the
charge-to-voltage conversion while source followers
provide buffering to external connections. The potential
change on the floating diffusion is dependent on the amount
of signal charge and is given by DVFD = DQ / CFD, where
DVFD is the change in potential on the floating diffusion,
DQ is the amount of charge, and CFD is the capacitance of
the floating diffusion node. Prior to each pixel output,
the floating di ffusion is returned to the RD level by the reset
clock, fR.
Figure 3. Channel Alignment Diagram
Luma
Channel
Blue
Channel
Red
Channel
Green
Channel
Pin 1
Last Active Pixel
(Luma Pixel #8160) First Active Pixel
(Luma Pixel #1)
12.25 Lines Spacing (122.5 mm)
9 Lines Spacing (90 mm)
9 Lines Spacing (90 mm)
(Center
(Edge)