BA7230 Rohm, BA7230 Datasheet - Page 6

• Manufacturer Part Number: BA7230
• Description: NTSC color TV signal encoder
• Manufacturer: Rohm

•
(1) Matrix circuit
The R, G and B inputs are clamped to 3.2V by the
clamp circuit and combined into signals E
E
Signal E
compensate for the signal's 6dB attenuation in the delay
line. To prevent overmodulation, signal E
1 / 1.14 and signal E
(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.
6
Multimedia ICs
B
Circuit operation
-E
E
E
E
Y
Y
R
B
by the resistance-adding matrix circuit.
3.58MHz (90 )
= 0.30E
– E
3.58MHz (0 )
– E
Y
is then amplified by the 6dB amplifier (pin 16) to
Y
Y
E
E
R - Y
= – 0.30E
B
R
= 0.70E
90
- E
- E
R
R
13
Y
Y
+ 0.59E
R - Y
B
3.58
90
R
-E
1
– 0.59E
R
Balanced
modulator
Balanced
modulator
Y
G
– 0.59E
s
Fig. 5
C carrier color signal
at 1 / 2.03 (pins 17 and 18).
Fig. 4
G
14
(combining of R-Y and B-Y)
+ 0.11E
B - Y
G
– 0.11E
G
B
+ 0.89E
+
B - Y
B
15
27k
5.1k
10k
BA7230LS
color signal
B
Carrier
R
Time
-E
B
Y
Y
, E
is output at
R
Y
-E
Y
and
The carrier color signal is mixed with color burst signals
and luminosity signals E
chronization signal is added) to create the NTSC com-
posite signal (E
(3) Switch circuit
Signal Ys (pin 23) switches between video input and
RGB composite signals. Performing this switching at
high speeds results in superimposition.
(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.
(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.
E
N
= E
+
E
Y'
B
2.03
9
+
TC
20pF
– E
XT
3.58MHz
E
1
VCXO
Fig. 7
1
R
1.14
Y
– E
R
1.2k
8
sin2 fst
RGB
COMPOSITE
VIDEO IN
13
N
).
Y
cos2 fst
7
Fig. 6
Y'
(to which a horizontal syn-
RGB
COMPOSITE
VIDEO IN
– 5dB
Y
OUT
Fig. 8
S
BA7230LS
HDP
(Half Down
Y
OUT
Pulse)
S