9
is also active during NTSC to obtain a good suppression of cross colour effects. The
demodulated colour difference signals are internally supplied to the delay line.
2A.8: RGB OUTPUT CIRCUIT AND BLACK-CURRENT STABILIZATION :
In the RGB control
circuit the signal is controlled on contrast, brightness and saturation. The ICs have a linear
input for external RGB signals. It is possible to use this input for the insertion of YUV signals.
Switching between RGB and YUV can be realised via the YUV-bit in subaddress 2BH. The
signals for OSD and text are internally supplied to the control circuit. The output signal has an
amplitude of about 2 Volts black-to-white at nominal input signals and nominal settings of the
various controls. To obtain an accurate biasing of the picture tube the ‘Continuous Cathode
Calibration’ system has been included in these ICs. A black level offset can be made with
respect to the level which is generated by the black current stabilization system. In this way
different colour temperatures can be obtained for the bright and the dark part of the picture.
The black current stabilization system checks the output level of the 3 channels and indicates
whether the black level of the highest output is in a certain window (WBC-bit) or below or
above this window (HBC-bit). This indication can be read from the status byte 01 and can be
used for automatic adjustment of the Vg2 voltage during the production of the TV receiver.
During switch-off of the TV receiver a fixed beam current is generated by the black current
control circuit. This current ensures that the picture tube capacitance is discharged. During the
switch-off period the vertical deflection is placed in an overscan position so that the discharge
is not visible on the screen.
2B. - MICROCONTROLLER WITH TELETEX DECODER: -
The integrated teletex decoder
with embedded microcontroller is a control system designed for TV sets with analogue picture
and sound control. The system also offers an on screen display (OSD) and IR remote control of
all functions.
3. TUNER: -
GDC Tuner EWT 5F3T1 is controlled by I2C bus through IC TDA 9361.The
tuning is based on frequency synthesis tunning
.
