TDA8841

Manufacturer Part NumberTDA8841
DescriptionI2C-bus controlled PAL/NTSC TV processor
ManufacturerPhilips Semiconductors
TDA8841 datasheet
 


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Philips Semiconductors
2
I
C-bus controlled PAL/NTSC/SECAM TV
processors
Adjustment of geometry control parameters
The deflection processor of the TDA8840/41/42/46/46A
offers 5 control parameters for picture alignment, viz:
S-correction
vertical amplitude
vertical slope
vertical shift
horizontal shift.
The TDA 8843/44/47/54H/57H offer in addition:
EW width
EW parabola width
EW corner parabola
EW trapezium correction.
vertical zoom
vertical scroll
It is important to notice that the IC’s are 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 EW output stage it is determined which
are the required values for the settings of S-correction, EW
parabola/width ratio and EW corner/parabola ratio. These
parameters can be preset via the I
any additional adjustment. The rest 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 meant 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 needed. 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.
December 16, 1997
For adjustment of the vertical shift and vertical slope
independent of each other, a special service blanking
mode can be entered by setting the SBL bit HIGH. In this
mode the RGB-outputs are blanked during the second half
of the picture. There are 2 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 right setting
and should not be changed.
If the vertical shift alignment is not required VSH should be
2
C-bus, and do not need
set to its mid-value (i.e. VSH = 1F). 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 EW width and
the horizontal shift. Finally (if necessary) the left- and
right-hand sides of the picture are aligned in parallel by
adjusting the EW trapezium control.
To obtain the full range of the vertical zoom function with
the TDA 8844/47/54H/57H the adjustment of the vertical
geometry should be carried out at a nominal setting of the
zoom DAC at position 19 HEX and the vertical scroll DAC
at position 1F HEX.
63
Tentative Device Specification
TDA884X/5X-N2 series