
1999 Sep 28
89
Philips Semiconductors
Preliminary Device Specification
TV signal processor-Teletext decoder with
embedded
μ
-Controller
TDA935X/6X/8X series
The types which are intended to be used in combination
with 110
°
picture tubes have an East-West control circuit
in stead of the AVL function. The additional controls for
these types are:
EW width
EW parabola width
EW upper and lower corner parabola correction
EW trapezium correction
Vertical zoom
and in some versions:
horizontal parallelogram and bow correction.
Chroma and luminance processing
The chroma band-pass and trap circuits (including the
SECAM cloche filter) are realised by means of gyrators
and are tuned to the right frequency by comparing the
tuning frequency with the reference frequency of the
colour decoder. The luminance delay line and the delay
cells for the peaking circuit are also realised with gyrators.
The circuit contains a black stretcher function which
corrects the black level for incoming signals which have a
difference between the black level and the blanking level.
Colour decoder
The ICs can decode PAL, NTSC and SECAM signals. The
PAL/NTSC decoder does not need external reference
crystals but has an internal clock generator which is
stabilised to the required frequency by using the 12 MHz
clock signal from the reference oscillator of the
μ
-Controller/Teletext decoder.
Underbad-signalconditions(e.g.VCR-playbackinfeature
mode), it may occur that the colour killer is activated
although the colour PLL is still in lock. When this killing
action is not wanted it is possible to overrule the colour
killerbyforcingthecolourdecodertotherequiredstandard
and to activate the FCO-bit (Forced Colour On) in
subaddress 21H.
The Automatic Colour Limiting (ACL) circuit (switchable
via the ACL bit in subaddress 20H) prevents that
oversaturation occurs when signals with a high
chroma-to-burst ratio are received. The ACL circuit is
designed such that it only reduces the chroma signal and
not the burst signal. This has the advantage that the colour
sensitivity is not affected by this function.
The SECAM decoder contains an auto-calibrating PLL
demodulator which has two references, viz: the divided 12
MHz reference frequency (obtained from the
μ
-Controller)
which is used to tune the PLL to the desired free-running
frequency and the bandgap reference to obtain the correct
absolute value of the output signal. The VCO of the PLL is
calibrated during each vertical blanking period, when the
IC is in search or SECAM mode.
The base-band delay line (TDA 4665 function) is
integrated. This delay line 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.
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 off set 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 V
g2
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.