TDA8376 Datasheet, PDF (37/44 Pages) NXP Semiconductors – I2C-bus controlled PAL/NTSC TV processors

Philips Semiconductors
I²C-bus controlled PAL/NTSC TV processors
Objective specification
TDA8376; TDA8376A
13.2 Adjustment of geometry control parameters
The deflection processor of the TDA8376/TDA8376A
offers nine control parameters for picture alignment:
• Vertical picture alignment
– S-correction
– vertical amplitude
– vertical slope
– vertical shift
• Horizontal picture alignment
– horizontal shift
– E-W width
– E-W parabola/width
– E-W corner/parabola
– E-W trapezium correction.
It is important to notice that the TDA8376/ TDA8376A is
designed for use with a DC-coupled vertical deflection
stage. This is the reason why a vertical linearity alignment
is not necessary (and therefore not available).
For a particular combination of picture tube type, vertical
output stage and E-W output stage it is determined which
are the required values for the settings of S-correction,
E-W parabola/width ratio and E-W corner/parabola ratio.
These parameters can be preset via the I²C-bus, and do
not need any additional adjustment. The remainder of the
parameters are preset with the mid-value of their control
range (i.e. 1FH), or with the values obtained by previous
TV-set adjustments.
The vertical shift control is intended for compensation of
off-sets in the external vertical output stage or in the
picture tube. It can be shown that without compensation
these off-sets will result in a certain linearity error,
especially with picture tubes that need large S-correction.
The total linearity error is in first order approximation
proportional to the value of the off-set, and to the square of
the S-correction required. The necessity to use the vertical
shift alignment depends on the expected off-sets in vertical
output stage and picture tube, on the required value of the
S-correction, and on the demands upon vertical linearity.
For adjustment of the vertical shift and vertical slope
independent of each other, a special service blanking
mode can be entered by setting the SB-bit HIGH. In this
mode the RGB-outputs are blanked during the second half
of the picture. There are two different methods for
alignment of the picture in vertical direction. Both methods
make use of the service blanking mode.
The first method is recommended for picture tubes that
have a marking for the middle of the screen. With the
vertical shift control the last line of the visible picture is
positioned exactly in the middle of the screen. After this
adjustment the vertical shift should not be changed. The
top of the picture is placed by adjustment of the vertical
amplitude, and the bottom by adjustment of the vertical
slope.
The second method is recommended for picture tubes that
have no marking for the middle of the screen. For this
method a video signal is required in which the middle of the
picture is indicated (e.g. the white line in the circle test
pattern). With the vertical slope control the beginning of the
blanking is positioned exactly on the middle of the picture.
Then the top and bottom of the picture are placed
symmetrical with respect to the middle of the screen by
adjustment of the vertical amplitude and vertical shift.
After this adjustment the vertical shift has the correct
setting and should not be changed.
If the vertical shift alignment is not required VSH should be
set to its mid-value (i.e. VSH = 1FH). Then the top of the
picture is placed by adjustment of the vertical amplitude
and the bottom by adjustment of the vertical slope. After
the vertical picture alignment the picture is positioned in
the horizontal direction by adjustment of the E-W width and
the horizontal shift. Finally (if necessary) the left and
right-hand sides of the picture are aligned in parallel by
adjusting the E-W trapezium control.
To obtain the full range of the vertical zoom function of the
TDA8376A the adjustment of the vertical geometry should
be carried out at a nominal setting of the zoom DAC at
position 19H.
1996 Jan 26
37