TDA9105A datasheet(19/31 Pages) STMICROELECTRONICS

19 / 31 page

OPERATING DESCRIPTION (continued)

Geometric Corrections

The principle is represented in Figure 20.

VDCIN

EW Amp

Vertical

Ramp

Keystone

Output

Corner

Vertical

Dynamic

Focus

Output

VDCIN

Sidepin Amp

Key Balance

Side Pin

Balance

Output

Analog

Multiplier

Figure 21 : Geometric Corrections Principle

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 Dynamic Horizontal 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

(10k

Ω). They can be DC coupled with external

circuitry.

VOUT = 2.5V + K1’(VRAMP -VDCIN)

+K1 (VRAMP -VDCIN)

+K1“(VRAMP -VDCIN)

K1 is adjustable by EW amp control (Pin 39)

K1’ is adjustable by KEYST control (Pin 38)

Dyn. Hor.

Phase Control

VOUT =4V + K2’(VRAMP -VDCIN)

+K2 (VRAMP -VDCIN)

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)

The output connection is 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.

TDA9105A

19/31

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