TDA9112A View Datasheet(PDF) - STMicroelectronics
Part Name
Description
MFG CO.
'TDA9112A' PDF : 60 Pages View PDF
TDA9112A
9.5 EW drive section
The goal of the EW drive section is to provide, on
pin EWOut, a waveform which, used by an external
DC-coupled power stage, serves to compensate
for those geometry errors of the picture that are
symmetric versus vertical axis across the middle
of the screen.
The waveform consists of an adjustable DC value,
corresponding to horizontal size, a parabola of 2nd
order for “pin cushion” correction, a linear for “key-
stone” correction, independent half-parabolas of
4th order for top and bottom corner corrections, S-
shape for “S” correction and W shape for “W” cor-
rection. All of them are adjustable via I²C-bus, see
Chapter 8 - page 27.
Refer to Figure 14, Figure 15 and chapter Chapter 7 -
page 22. The adjustments of these correction
waveforms have no effect in the middle of the ver-
tical scan period (if the VPOS control is adjusted to
its medium value). As they are summed, the re-
sulting waveform tends to reach its maximum span
at top and bottom of the picture. The voltage at the
EWOut is top and bottom limited (see parameter
VEW). According to Figure 15, especially the bottom
limitation seems to be critical for maximum hori-
zontal size (minimum DC). Actually it is not critical
since the parabola component must always be ap-
plied to obtain a picture without pin cushion distor-
tion. As all the components of the resulting correc-
tion waveform are generated from an internal line-
ar vertical sawtooth waveform bearing VSIZE and
VPOS adjustments, they all track with vertical am-
plitude and position, thus being fixed vertically on
the screen. They are not affected by C- and S-cor-
rections, by prescale adjustments (VSAG and
VPOF), by vertical breathing compensation and by
vertical moire cancellation. The sum of compo-
nents other than DC is conditionally affected by
value in HSIZE I²C-bus control in reversed sense.
Refer to electrical specifications for value. This
tracking with HSIZE can be switched off by
EWTrHSize I²C-bus bit. The DC value, adjusted
via HSIZE control, is also affected by voltage on
HEHTIn input, thus providing a horizontal breathing
compensation. The effect of this compensation is
controlled by HEHTG. The resulting waveform is
conditionally multiplied with voltage on HPLL1F,
which depends on frequency. Refer to electrical
specifications for values. This tracking with fre-
quency provides a rough compensation of varia-
tion of picture geometry with frequency and allows
to fix the adjustment ranges of I²C-bus controls
throughout the operating range of horizontal fre-
quencies. It can be switched off by EWTrHFr I²C-
bus bit (off by default). The functionality is ex-
plained in Figure 13. The upper part gives the influ-
ence on DC component, the lower part on AC
component, showing also the tracking with HSIZE.
Grey zones give the total span of breathing correc-
tion using the whole range of input operating volt-
age on HEHTIn input and whole range of adjust-
ment of HEHTG register.
The EW waveform signal is buffered by an NPN
emitter follower, the emitter of which is directly
routed to EWOut output. It is internally biased (see
electrical specifications for current value).
42/60
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