tda8374bh NXP Semiconductors, tda8374bh Datasheet - Page 53

• Manufacturer Part Number: tda8374bh
• Description: Tda837x Family I?c-bus Controlled Economy Pal/ntsc And Ntsc Tv-processors
• Manufacturer: NXP Semiconductors

Philips Semiconductors
Adjustment of geometry control parameters
The deflection processor of the TDA8373 and TDA8374
offers 5 control parameters for picture alignment:
The TDA8375, TDA8377, TDA8375A and TDA8377A offer
in addition the following functions for horizontal alignment:
It is important to notice that the ICs 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 and
vertical output stage and E-W output stage, it is
determined which are the required values for the settings
of S-correction. These parameters can be preset via the
I
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 1st 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
1997 Jul 01
2
C-bus and do not need any additional adjustment.
Vertical picture alignment
– S-correction
– vertical amplitude
– vertical slope
– vertical shift
– Horizontal shift alignment.
E-W width
E-W parabola/width
E-W corner/parabola
E-W trapezium correction.
I
and NTSC TV-processors
2
C-bus controlled economy PAL/NTSC
53
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 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 adjusting the vertical
amplitude and the bottom by adjusting 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
symmetrically 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). The top of the picture
is then placed by adjusting the vertical amplitude and the
bottom by adjusting the vertical slope. After the vertical
picture alignment the picture is positioned in the horizontal
direction by adjusting the horizontal shift.
To obtain the full range of the vertical zoom function with
the TDA8375 and TDA8377 the adjustment of the vertical
geometry should be carried out at a nominal setting of the
zoom DAC at position 19H.
TDA837x family
Preliminary specification