TDA9103 datasheet(17/27 Pages) STMICROELECTRONICS

17 / 27 page

Analog.

Multiplier

E/W-CENT

E/W-AMP

Vertical Ramp

Figure 21 : Parabola Generation Principle

PARABOLA GENERATION FOR EAST-WEST

CORRECTION (see Figure 21)

Starting from the vertical ramp a parabola is gen-

erated for E/W correction.

The core of the parabola generator is an analog

multiplier which generates a current in the form :

I= k (VRAMP -VMID)

Where VRAMP is the vertical ramp, typically com-

prised between 2 and 5V, VMID is a DC voltage with

a nominal value of 3.5V, but adjustable in the range

3.2V

→ 3.8V in order to generate a dissymmetric

parabola if required (keystone adjustment).

The current is converted into voltage through a

variable gain transresistance amplifier. The gain,

controlled by the voltage on Pin 37 (E/W-AMP) can

be adjusted in the ratio 3/1.

The parabola is available on Pin 36 by the way of

an emitter follower which has to be biased by an

external resistor (10k

Ω). It must be AC coupled with

external circuitry.

The typical parabola amplitude (AC), with the DC

control voltages V37 and V38 set to 4V, is 2V.

It is important to note that the parasitic parabola

during the discharge of the vertical oscillator ca-

pacitor is suppressed.

VERTICAL PART (see Figure 22)

The vertical part generates a fixed amplitude ramp

which can be affected by a S correction shape.

Then, the amplitude of this ramp is adjusted to drive

an external power stage.

The internal reference voltage used for the vertical

part is available between Pin 26 and Pin 24. It can

be used as voltage reference for any DC adjusment

to keep a high accuracy to each adjustment. Its

typical value is :

V26 =VREF =8V.

The charge of the external capacitor on Pin 27

(VCAP) generates a fixed amplitude ramp between

the internal voltages, VL (VL =VREF/4) and VH

(VH = 5/8

⋅ VREF).

REF

Osc

Cap

19R

Sampling

Cap

REF

S Correction

VERT-OUT

VERT-AMP

Parabola

Generator

EW-AMP

KEYST

EW-OUT

OSCIL

SYNCHRO

V-SYNC

Disch.

Charge Current

Transconductance

Amplifier

29 S-CENTER

S-AMP

Figure 22 : Vertical Part Block Diagram

TDA9103

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