CXA1870 SONY [Sony Corporation], CXA1870 Datasheet - Page 30

• Manufacturer Part Number: CXA1870
• Description: Color TV Y/C/Jungle
• Manufacturer: SONY [Sony Corporation]

3. RGB interface system
Note)
Auto cut-off
The signal is then separated into color difference signals R-Y, B-Y and G-Y by the matrix circuit, passed
through the Y/C MIX circuit, and input together with the Y signal to the RGB interface system block.
The detective axis (Japan/US) can be switched by the I
YS/YM switching is performed according to the amplitude of the OSD RGB input blanking signal input from
Pin 11.
The R, G and B signals of the Y/C system pass through the RGB switch (BLUE and BLACK ON/OFF) and
receive picture control. These signals are mixed with the digital R, G and B signals (specified input level 0
to 5 V DC) input from Pins 12, 13 and 14, passed through the dynamic color, gamma correction, bright
control, drive adjustment (R channel is fixed, G and B channels are variable.), cut-off adjustment (R channel
is fixed, G and B channels are variable.) and auto cut-off DC level shift circuits, and then output from Pins
16, 18 and 20 as the R, G and B signals. The RGB output amplitude has a limit voltage whose setting
value can be controlled with the I
screen display of channels, etc. and the display level can be set with the I
The signal input to Pin 23 (ABL IN) is compared with the internal reference voltage and is then integrated by
the capacitor connected to Pin 25 (ABL LPF) for picture and brightness control. Picture ABL mode and
combined picture ABL and brightness ABL mode can be switched with the I
When the digital R, G and B signals and OSDBLK signal are not used, connect Pins 11, 12, 13 and 14 to
GND.
For white balance, drive control (gain control between R, G and B outputs) and cut-off control (black side
DC level control) are involved. This IC uses the I
is formed between the IC and CRT to achieve auto cut-off control.
This auto cut-off arrangement makes it possible to compensate for CRT changes with time. To absorb the
CRT variance, the cut-off voltages of the G and B outputs are adjusted by the I
The auto cut-off loop is configured as described below.
The loop mentioned above determines the shift level of the R, G and B outputs and lets the capacitances
connected to Pins 15, 17 and 19 hold the DC shift level during the 1 V period. If the voltage at any one of
Pins 15, 17 or 19 is less than 4.2 V, the status register IK (bit 6) becomes “1”. Use this information to blank
the R, G and B outputs with the I
the I
(1) R, G and B reference pulses for auto cut-off, shifted 1H each in the order mentioned, are added to
(2) The IK of each of the R, G and B outputs is converted to a voltage and input to Pin 21.
(3) The voltage input to Pin 21 is compared with the reference voltage in the IC to change the DC level
2
0 to 1.5 V
1.5 to 3.5 V
3.5 to 5.5 V
C bus register.
the top of the picture.
of the reference pulses.
TV (Y/C input)
TV –6 dB
Black
2
C bus register. The positions of the reference pulses can be changed by
2
C bus register. The digital R, G and B signals are mainly used for on
—30—
2
C bus register for drive control. For cut-off control, a loop
2
C bus register.
2
C bus register.
2
C bus register.
2
C bus register.
CXA1870S