BA7230LS View Datasheet(PDF) - ROHM Semiconductor
Part Name
Description
Manufacturer
BA7230LS Datasheet PDF : 8 Pages
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Multimedia ICs
•Circuit operation
(1) Matrix circuit
The R, G and B inputs are clamped to 3.2V by the
clamp circuit and combined into signals EY, ER-EY and
EB-EY by the resistance-adding matrix circuit.
EY = 0.30ER + 0.59EG + 0.11EB
ER – EY = 0.70ER – 0.59EG – 0.11EB
EB – EY = – 0.30ER – 0.59EG + 0.89EB
Signal EY is then amplified by the 6dB amplifier (pin 16) to
compensate for the signal's 6dB attenuation in the delay
line. To prevent overmodulation, signal ER-EY is output at
1 / 1.14 and signal EB-EY at 1 / 2.03 (pins 17 and 18).
BA7230LS
27kΩ
5.1kΩ
Y
10kΩ
13
R
14
G
15
B
Fig. 4
(2) Balanced modulator circuit
Color difference signals are modulated (rectangular 2-
phase balanced modulation) with color subcarriers
(3.58MHz) having a 90° phase difference. This is
called the carrier color signal.
C carrier color signal
(combining of R-Y and B-Y)
R-Y
B-Y
θ
90°
Time
1
3.58 µs
R-Y
90°
θ
EB - EY
3.58MHz (0°)
ER - EY
3.58MHz (90°)
Balanced
modulator
Balanced
modulator
B-Y
+
Carrier
color signal
Fig. 5
6
BA7230LS
The carrier color signal is mixed with color burst signals
and luminosity signals EY' (to which a horizontal syn-
chronization signal is added) to create the NTSC com-
posite signal (EN).
EN = EY' + ER – EY cos2πfst
1.14
+ EB – EY sin2πfst
2.03
(3) Switch circuit
Signal Ys (pin 23) switches between video input and
RGB composite signals. Performing this switching at
high speeds results in superimposition.
RGB
COMPOSITE
YS
VIDEO IN
OUT
Fig. 6
(4) Color subcarrier oscillator circuit
The subcarrier oscillator circuit for RGB input. This cir-
cuit is synchronized with the video input color burst sig-
nal extracted by BFP (burst flag pulses) during super-
imposition, preventing any unnatural color disturbance
due to switching between RGB and video input.
This oscillator circuit generates the RGB color burst
signal. An attached variable resistor can be used to
change the amplitude of the color burst signal and to
adjust its phase relative to the video color burst signal.
This oscillator circuit remains in the free-running state
when there is no video input.
VCXO
9
8
7
TC1
R13
20pF 1.2kΩ
XT1
3.58MHz
RGB
COMPOSITE
– 5dB
VIDEO IN
YS
OUT
HDP
(Half Down
Pulse)
Fig. 7
Fig. 8
(5) During superimposition, video input can be lowered
by about 5dB using an HDP (half-down pulse), darken-
ing the background and making RGB input easier to
see.
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