BU1424K Ver la hoja de datos (PDF) - ROHM Semiconductor
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BU1424K Datasheet PDF : 30 Pages
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Multimedia ICs
BU1424K
•Circuit operation
(1) Overview
The BU1424K converts digital images and video data
with an 8-bit configuration to 9-bit composite signals
(VOUT), luminance signals (YOUT), and chrominance
signals (COUT) for the NTSC, PAL, and PAL60 for-
mats, and outputs the converted data as analog TV
signals.
The user may select whether VOUT consists of chromi-
nance signals that have passed through a chrominance
band pass and luminance signals that have been
mixed, or luminance signals that have passed through
a chrominance trap and luminance signals that have
not passed through a chrominance trap. The F charac-
teristic of this chrominance trap may be selected from
among three available types. Since YOUT normally
does not pass through the trap, it is optimum for the S
pin. COUT normally passes through the chrominance
band pass, and is thus highly resistance to dot interfer-
ence. In addition, when used in the doubled clock
mode, it passes through an interpolator filter, and for
that reason is able to reproduce even cleaner image
quality.
A correspondence can be set up between input digital
image data and Video-CD and CD-G decoder output.
Output TV signals, in addition to switching among the
NTSC, PAL, and PAL60 modes, can be switched be-
tween the interlace and non-interlace modes.
The data clock input to the VCLK pin can also be input
as a doubled clock for the data rate (in doubled clock
modes). In doubled clock modes, data is read and
processed at the rising edge of an internal clock that
has been divided in half. In ordinary clock modes, data
is read and processed at the rising edge of the clock
that has the same phase as the input clock. Two input
data formats are supported: 24-bit RGB (4: 4: 4) and
16-bit YUV (4: 2: 2). These are input to RD0 to 7, GD0
to 7, and BD0 to 7, respectively. The selected input for-
mat can be switched using the IM0 and IM1 pin input.
When the OSDSW pin is set to the "Enabled" (H) state,
data input to the ROSD, GOSD, and BOSD pins be-
comes effective, making it possible to input 7-color (8
including black) chrominance data. At the same time, a
clock with a frequency half that of the internal clock is
output from the PIXCLK pin. As a result, the PIXCLK
pin can easily be directly connected to the OSD IC
clock input pin, and the OSDSW pin can be directly
connected to the BLK output pin. Thus, the BU1424K
and the OSD IC can be synchronized, and OSD text
with a burster trimmer stacker feature can be used.
If the input data is in the RGB format, it is converted to
YUV. If it is in the YUV format, it is converted from the
CCIR-601 format to level-shifted YUV data. The YUV
data is then adjusted to the 100IRE level in the NTSC,
PAL, and PAL60 modes, and U and V data is phase-
adjusted by a sub-carrier generated internally, and is
modulated to chrominance signals.
Ultimately, elements such as the necessary synchro-
nization level, the color blanking level, and burst sig-
nals are mixed, and pass through the 9-bit DAC to be
output as NTSC or PAL composite signals, luminance
signals, and chrominance signals (conforming to RS-
170A). At this point, the DAC is operating at twice the
internal clock, making it possible to reduce the number
of attachments.
Furthermore, luminance signal output and chrominance
signal output can be turned off. At this point, it is possi-
ble to reduce the level of power consumption.
The DAC output is current output. If a resistor of a
specified value is connected to the IR pin, 2.0VP-P out-
put can be obtained by connecting 75Ω to the VOUT
pin as an external resistor. As a result, normally, when
a video input pin (75Ω terminus) is connected, the out-
put is approximately 1.0VP-P voltage output at a white
100% level.
(2) Specifying the mode
1) Power saving mode
With the BU1424K, setting the YCOFF pin to HIGH
turns off the output from the YOUT and COUT pins of
the DAC output, enabling use in the low power con-
sumption mode.
Table 1: Low power consumption mode with the YCOFF pin
Pin No.
Pin name
Output mode and power consumption
YCOFF
VOUT pin
YOUT pin
COUT pin
Power consumption (Typ.)
48
LOW
Composite signal
Luminance signal Chrominance signal
0.45W
HIGH
Composite signal
No output (0V)
No output (0V)
0.25W
12
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