STV2000 datasheet(24/38 Pages) STMICROELECTRONICS

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STV2000

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OPERATING DESCRIPTION (continued)

3.4 Geometric Corrections

The principle is represented in Figure 14.

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.

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

Pin Cushion, Keystone), the combination of the

tracking function, maximum vertical amplitude,

maximum or minimum vertical position and maxi-

mum gain on the DAC control may lead to output

stage saturation. This must be avoided by limiting

the output voltage with appropriate I

2C register

values. For the E/W part and the dynamic horizon-

tal phase control part, a sawtooth-shaped differen-

tial current in the following form is generated:

∆I’ = k’ . (V

OUT - VDCMID).

Then

∆I and ∆I’ are added and converted into volt-

age for the E/W part.

Each of the two E/W components or the two dy-

namic horizontal phase control components may

be inhibited by their own I2C select bit.

Internal EW correction voltage is not available di-

rectly on the output pin. The EW correction is ob-

tained with the feedback voltage (Pin 27: EWBin)

which generates a modulating current in the diode

(Pin 28). In addition, the horizontal width is I

2C-

controlled.

The dynamic horizontal phase control drives the

H-position internally, moving the HFLY position on

the horizontal sawtooth in the range of

± 2.8 %T

both for side pin balance and parallelogram.

Figure 14. Geometric Corrections Principle

3.5 E/W

EWOUT = EWDC +K1 (VOUT - VDCMID) +K2 (VOUT - VDCMID)

K1 is adjustable via the keystone I2C register. K2 is adjustable via the E/W amplitude I2C register.

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