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Geometry and Focus Control Section
AN1290
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STMicroelectronics Confidential
All corrections (Pincushion, Corner (symmetric and asymmetric), Keystone, Parallelogram, Side pin
balance) are also computed as functions of V
23
- 3.5V. This means that for a given point on the
screen, constant corrections will correspond when changing vertical amplitude and position.
Consequently, the outlook of the display vertical border will remain unchanged when modifying
these adjustments. This is the “tracking with Vertical” function.
In the TDA9112A, the “tracking” feature also applies to S and C corrections of the vertical sawtooth.
6.1.6
Dynamic Corrections
The TDA9112 provides the following dynamic corrections (e.g. Focus and/or Brightness):
●
On pin 11 a composite waveform HVDyCor for Dynamic Focus or Dynamic Brightness
compensation. It corresponds to the sum of two parabolic waveforms with upwards concavity
∪
, one at vertical frequency, one at horizontal frequency. Through I²C, you can adjust both
amplitudes (V Focus (Register 06) can be set to 0, but not H Focus (Register 04)) as well as
the symmetry of H parabola (Register 05).
●
On pin 32, a parabolic waveform at vertical VDyCor frequency, with selectable polarity through
I²C programming (Register 15).
This flexible architecture allows various combinations, like:
●
separate V Focus (positive or negative) and H Focus,
●
composite Focus,
●
V Focus (positive or negative) and composite Dynamic Brightness.
The TDA9113 has only a Horizontal parabola on pin 11; TDA9115 and TDA9116 provide only the
vertical parabola on pin 32, while pin 11 is devoted to Breathing compensation.
The TDA9112A provides all the features of the TDA9112 and, in addition to these features, on pin
11:
●
Both signal polarities may be selected (1Fd1): either upwards concavity
∪
of the composite
waveform with the apex at 2.1V, or downwards concavity
∩
with the apex at 7V;
●
In order to best comply with the focus requirements of modern flat screens, the shape of the H
“parabola” may be continuously varied through a 7-bit I²C register (Register 18), from true
parabola (power index 2) to power index 4, while its amplitude remains basically unaffected.
6.1.7
Horizontal Dynamic Focus/Brightness
The Horizontal Dynamic Focus/Brightness features are available on the HVDyCor pin (pin 11).
In order to provide a parabolic voltage synchronous with the Horizontal components, a synchronous
sawtooth voltage is first internally generated with a current source that charges a capacitor. An
internal AGC system maintains a constant amplitude of the sawtooth.
The capacitor discharge takes place inside flyback, through a 500
Ω
resistor, which leads to small
but not negligible discharge time of 500 ns (typical).
The ramp voltage (referenced to its mean value) is then squared to finally provide on pin 11 a
parabolic voltage with upwards concavity
∪
and an amplitude between 1V and 3.5V which is
adjustable through I²C programming (Register 04).
Usually, the amplitude of the HFocus parabola should increase when the HSize increases. For this
purpose, you can select the “Amplitude Tracking” feature through I²C programming (Sad04h/d7).
Because the parabola is obtained by squaring an internal sawtooth, its amplitude will vary to the
squared value of the amplitude setting.
