Sanyo VPC-CG20 Service Manual page 4

1-2. CP1 and VF1 CIRCUIT DESCRIPTION
1. Circuit Description
1-1. Digital clamp
The optical black section extracts averaged values from the
subsequent data to make the black level of the sensor output
data uniform for each line. The optical black section averaged
value for each line is taken as the sum of the value for the
previous line multiplied by the coefficient k and the value for
the current line multiplied by the coefficient k-1.
1-2. 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 image sensor 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.
1-3. 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.
1-4. SDRAM controller
This circuit outputs address, RAS, CAS and CLOCK data for
controlling the SDRAM. It also refreshes the SDRAM.
1-5. Digital encoder
It generates chroma signal from color difference signal.
2. Outline of Operation
When the shutter opens, the picture data from CMOS passes
through the A/D and CDS, and is then input to the ASIC as
digital data. The AF, AE, AWB, shutter, and AGC value are
computed 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 genera-
tion is carried out. Each pixel is interpolated from the sur-
rounding data as being either R, G, and 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.
3. LCD Block
The LCD display circuit is located on the CP1 board and VF1
board, and consists of components such as a power circuit.
The signals from the ASIC are 8-bit digital signals, that is
input to the LCD directly. The 8-bit digital signals are con-
verted to RGB signals inside the LCD driver circuit . This LCD
has a 3-wire serial, and functions such as the brightness and
image quality are controlled.
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 in potential is smaller, the element opens and
the LCD become brighter.
In addition, the timing pulses for signals other than the video
signals are also input from the ASIC directory to the LCD.
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