TDA9105A View Datasheet(PDF) - STMicroelectronics
Part Name
Description
MFG CO.
'TDA9105A' PDF : 31 Pages View PDF
TDA9105A
OPERATING DESCRIPTION (continued)
Geometric Corrections
The principle is represented in Figure 20.
Figure 21 : Geometric Corrections Principle
Vertical
Ramp
Analog
Multiplier
X2
VDCIN
Vertical
Dynamic
Focus
Output
EW Amp
VDCIN
Keystone
X2
Corner
EW
Output
Sidepin Amp
VDCIN
Key Balance
Side Pin
Balance
Output
Starting from the vertical ramp, a parabola shaped
is generatedfor E/W correction, dynamichorizontal
phase control correction, and vertical dynamic Fo-
cus correction.
The core of the parabola generator is an analog
multiplier. The output current of which is equal to :
∆I = k (VRAMP - VDCIN)2.
Where VRAMP is the vertical ramp, typically com-
prised between 2 and 5V, VDCIN is a vertical DC
input adjustable in the range 3.2V → 3.8V in order
to generate a dissymmetric parabola if required
(keystone adjustment).
In order to keep good screen geometry for any end
user preferences adjustment we implemented the
possibility to have “geometry tracking”. To enable
the “tracking” function, the VDCOUT must be con-
nected to VDCIN.
It is possible to inhibit VPOS tracking by applying a
fixed DC voltage on the VDCIN Pin.
This DC voltage in that case must be taken from
the vertical reference and adjusted to 3.5V with an
external bridge resistor.
Due to large output stages voltage range (E/W,
BALANCE, FOCUS), the combination of tracking
function with maximum vertical amplitude max. or
min. vertical position and maximumgain on the DC
control inputs may leads to the output stages satu-
ration. This must be avoided by limiting the output
voltage by apropriate DC control voltages.
For E/W part and DynamicHorizontal phasecontrol
part, a sawtooth shaped differential current in the
followingform is generated: ∆I’ = k’ (VRAMP -VDCIN).
Then ∆I and ∆I’ are added together and converted
into voltage.
For E/W part corner purpose, the following current
form is generated and added before voltage con-
version ∆I” = k” (VRAMP - VDCIN)4.
These two parabola are respectively available on
Pin 37 and Pin 40 by the way of an emitter follower
which has to be biased by an external resistor
(10kΩ). They can be DC coupled with external
circuitry.
EW
VOUT = 2.5V + K1’ (VRAMP - VDCIN)
+ K1 (VRAMP - VDCIN)2
+ K1“ (VRAMP - VDCIN)4
K1 is adjustable by EW amp control (Pin 39)
K1’ is adjustable by KEYST control (Pin 38)
Dyn. Hor.
VOUT = 4V + K2’ (VRAMP - VDCIN)
Phase Control
+ K2 (VRAMP - VDCIN)2
K2 is adjustable by SPB amp control (Pin 42)
K2’ is adjustable by KEYBAL control (Pin 41)
For vertical dynamic focus part, only a constant
amplitude parabola is generated in the form :
VOUT = 6V - 0.75 x (VAMP - VDCIN)2.
The output connectionis the same as the two other
corrections (Pins 37-40).
It is important to note that the parasitic parabola
during the discharge of the vertical oscillator ca-
pacitor is suppressed.
19/31
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