STV2001 datasheet(29/46 Pages) STMICROELECTRONICS

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STV2001

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The gain of this stage can be adjusted (

± 25%) de-

pending on its register value.

The mean value of this ramp is driven by its own

I2C register (vertical position) with :

VPOS = 7/16 x VREF-V = ± 300 mV.

Usually VOUT is sent through a resistive divider to

the inverting input of the booster. Since VPOS de-

rives from VREF-V, the bias voltage sent to the non-

inverting input of the booster should also derive

from VREF-V to optimize the accuracy

(see Figure 14).

Figure 14. AGC Loop Block Diagram

14.3.3 - Basic Equations

As a first approximation, the amplitude of the ramp

on Pin 7 (VOUT) is calculated as follows:

VOUT - VPOS = (VOSC - VDCMID) x (1 + 0.25 (VAMP))

where :

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

Pin 5, typically 3.6V)

VOSC = V5 (ramp with fixed amplitude)

VAMP = -1 as minimum vertical amplitude register

value and +1 as maximum value.

VPOS is calculated according to:

VPOS = VDCMID + (0.4x VP )

where VP = -1 and +1 as respectively minimum

and maximum vertical position register value.

The current available on Pin 6 is:

IOSC =

x VREF x COSC x f

where

COSC = capacitor connected on Pin 6

f = synchronization frequency.

14.3.4 - Geometric Corrections

The principle is represented in Figure 15.

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.

The parabola generator consists of an analog mul-

tiplier, the output current of which is equal to :

∆I = k x (VOUT - VDCMID)

where VOUT is the vertical output ramp (typically

between 2 and 5 V) and VDCMID is 3.6 V

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

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

sition, the sawtooth shifts by

±0.4 V.

The "geometry tracking" feature ensures a correct

screen geometry for any end user adjustment. It

generates non-symmetric parabola dependent on

the vertical position. To avoid Vertical EHT com-

pensation (VBreathing) from affecting the geome-

try correction, an additional Buffer Amplifier is

used for VBreathing.

VSYNCIN

SYNCHRO

OSCILLATOR

DISCH.

OSC

CAP

CHARGE CURRENT

TRANSCONDUCTANCE

AMPLIFIER

SAMPLING

CAPACITANCE

S CORRECTION

BREATH

VOUT

VPOSITION

SUB09/7bits

VERT AMP

SUB08/7bits

VS AMP

SUB0A/7bits

SAMPLING

Vlow

Sawth

Disch

REF

I2C

sub14

/6bits

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