TDA9109A datasheet(35/47 Pages) STMICROELECTRONICS

35 / 47 page

TDA9109A

35/47

Figure 16. AGC Loop Block Diagram

3.4 Basic Equations

In first approximation, the amplitude of the ramp

on Pin 23 (VOUT) is:

VOUT - VPOS = (VOSC -VDCMID)

. (1 + 0.3 (V

AMP))

where:

VDCMID = 7/16 VREF (middle value of the ramp on

Pin 22, typically 3.6V)

VOSC =V22 (ramp with fixed amplitude)

VAMP = -1 for minimum vertical amplitude register

value and +1 for maximum

VPOS is calculated by:

VPOS = VDCMID + 0.4 VP

where VP = -1 for minimum vertical position regis-

ter value and +1 for maximum.

The current available on Pin 22 is:

IOSC =

. V

REF

. C

OSC

. f

where COSC = capacitor connected on Pin 22 and

f = synchronization frequency.

Geometric Corrections

The principle is represented in Figure 17.

Starting from the vertical ramp, a parabola-shaped

current is generated for E/W correction (also

known as Pin Cushion correction), dynamic hori-

zontal phase control correction, and vertical dy-

namic focus correction.

The parabola generator is made by an analog mul-

tiplier, the output current of which is equal to:

∆I= k . (VOUT - VDCMID)

where VOUT is the vertical output ramp (typically

between 2 and 5V) and VDCMID is 3.6V

(for VREF-V = 8.2V). The VOUT sawtooth is typical-

ly centered on 3.6V. By changing the vertical posi-

tion, the sawtooth shifts by

±0.4V.

To provide good screen geometry for any end user

adjustment, the TDA9109A has the “geometry

tracking” feature which allows generation of a dis-

symetric parabola depending on the vertical posi-

tion.

Due to the large output stage voltage range (E/W

Pin Cushion, Keystone, E/W Corner), the combi-

nation of the tracking function, maximum vertical

amplitude, maximum or minimum vertical position

and maximum gain on the DAC control may lead

to output stage saturation. This must be avoided

by limiting the output voltage with appropriate I

VSYNCIN 2

Synchro

Polarity

Oscillator

Discharge.

OSC

CAP

Sampling

Capacitance

S Correction

VS Amp

sub-add 07/7bits

Cor_C

sub-add 08/7bits

C Correction

18 BREATH

23 VOut

Vert. Amp

sub-.05/7bits

VMoiré

sub.0C/7bits

V Position

sub.06/7bits

Vlow

sawth

disch.

REF

Charge Current

Transconductance Amplifier

TDA9109A Datasheet(PDF) 35 Page - STMicroelectronics

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