– 4 –
6
. Circuit Description
6-1. Digital clamp
The optical black section of the CCD extracts averaged val-
ues from the subsequent data to make the black level of the
CCD output data uniform for each line. The optical black sec-
tion of the CCD averaged value for each line is taken as the
sum of the value for the previous line multiplied by the coeffi-
cient k and the value for the current line multiplied by the
coefficient 1-k.
6-2. Signal processor
1.
γ
correction circuit
This circuit performs (gamma) correction in order to maintain
a linear relationship between the light input to the camera
and the light output from the picture screen.
2. Color generation circuit
This circuit converts the CCD data into RGB signals.
3. Matrix circuit
This circuit generates the Y signals, R-Y signals and B-Y sig-
nals from the RGB signals.
4. Horizontal and vertical aperture circuit
This circuit is used gemerate the aperture signal.
6-3. AE/AWB and AF computing circuit
The AE/AWB carries out computation based on a 64-segment
screen, and the AF carries out computations based on a 6-
segment screen.
6-4. SDRAM controller
This circuit outputs address, RAS, CAS and AS data for con-
trolling the SDRAM. It also refreshes the SDRAM.
6-5. Communication control
1. SIO
This is the interface for the 8-bit microprocessor.
2. PIO/PWM/SIO for LCD
8-bit parallel input and output makes it possible to switch be-
tween individual input/output and PWM input/output.
6-6. TG/SG
Timing generated for 3 million pixel CCD control.
6-7. Digital encorder
It generates chroma signal from color difference signal.
7. Outline of Operation
When the shutter opens, the reset signals (ASIC and CPU)
and the serial signals (“take a picture” commands) from the
8-bit microprocessor are input and operation starts.
When the TG/SG drives the CCD, picture data passes through
the A/D and CDS, and is then input to the ASIC as 10-bit
data. The AF, AE, AWB, shutter, and AGC value are com-
puted from this data, and three exposures are made to obtain
the optimum picture. The data which has already been stored
in the SDRAM is read by the CPU and color generation is
carried out. Each pixel is interpolated from the surrounding
data as being either Ye, Cy, Mg or B primary color data to
produce R, G and B data. At this time, correction of the lens
distortion which is a characteristic of wide-angle lenses is
carried out. After AWB and
γ
processing are carried out, a
matrix is generated and aperture correction is carried out for
the Y signal, and the data is then compressed by JPEG and
is then written to card memory (SD card).
When the data is to be output to an external device, it is taken
data from the memory and output via the USB I/F. When played
back on the LCD and monitor, data is transferred from memery
to the SDRAM, and the image is then elongated so that it is
displayed over the SDRAM display area.
8. LCD Block
LCD block is in the CP1 board, and it is constructed by VCOM
gerenated circuit etc. The video signal from the ASIC are in-
put to LCD panel directly by 6-bit digital signal, and are con-
verted into RGB signals by driver circuit in the LCD panel.
Because the LCD closes more as the difference in potential
between the VCOM (common polar voltage: AC) and the R,
G and B signals becomes greater, the display becomes darker;
if the difference inpotential is smaller, the element opens and
the LCD becomes brighter. And also timing pulse except video
signal are input at LCD panel directly from ASIC.
Summary of Contents for Xacti VPC-S1
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