STV223XD datasheet(20/76 Pages) STMICROELECTRONICS

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STV223XD/224XC - FUNCTIONAL DESCRIPTION

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3.4 VIDEO CIRCUIT

RGB Inputs

The RGB (OSD) input has priority over the exter-

nal RGB input. The RGB (EXT) source is matrixed

into YUV signals for color and contrast adjust-

ments. The brightness is adjusted according to the

internal and external RGB and OSD RGB signals.

The Contrast Control regulates both external and

internal RGB signals and has a maximum attenua-

tion of -24 dB. It also regulates the OSD RGB sig-

nal and its maximum attenuation is limited to

-12 dB. The Contrast Control for RGB (OSD) input

can be disabled via the bus. The brightness of the

RGB (OSD) input varies according to the main

brightness level.

The RGB (EXT) insertion signal can be disabled or

forced via the bus. A fast blanking detector on an

external fast blanking input and OSD fast blanking

input operate during frame retrace. The Fast

Blanking detection status is sent to the I²C bus

read register.

The OSD fast blanking input has several functions:

OSD Insertion Control, RGB Output Blanking or

Half Contrast Control.

Half-contrast Control Pin (TQFP64)

The 6 dB gain reduction will be applied to the inter-

nal YUV signals when the half-contrast function is

turned ON, and the voltage of the half-contrast in-

put exceeds the threshold (0.7 V Typ.).

The Half Contrast function is also available in the

SDIP56 package. The Half Contrast input is com-

bined with the FBOSD input.

Automatic Cut-off Current Loop

The Cut-off Loop range is 2 V (the cut-off level of

the RGB outputs is between 1.5 V and 3.5 V,

2.5 V Typ.). The cut-off current is measured se-

quentially during the three lines after the internal

frame blanking signal (the blue cathode current is

measured first, then the green and red). The Leak-

age cathode current is measured during frame

blanking and is memorized on an internal capaci-

tor. Cut-off pulses can be inserted after the exter-

nal vertical oversize blanking signal. The Cut-off

loop can be frozen via the bus. To prevent cut-off

lines from being visible in 16/9 mode, cut-off puls-

es are not inserted when the cut-off loop is frozen.

Warm-up Detector

At power on, the cut-off loop is not active and high

DC levels are inserted during "cut-off" lines. The

Cut-off loop will be active when the cathode cur-

rent reaches the warm-up detection threshold.

This causes the picture to be displayed from a

dark screen. The RGB outputs are blanked until

cut-off current is close to the reference voltage.

The manual cut-off mode can be selected via the

I²C bus. In this mode, the ICATH input pin is inac-

tive and cut-off pulses are not inserted. The RGB

black levels are independently controlled by three

I²C bus registers (8-bit resolution). The black level

of each RGB output can be adjusted within a

range of 2.5V typ.

Beam Current Limiter DC Voltage Input (BCL)

The BCL will first decrease the contrast and then

the brightness when the contrast attenuation

reaches -5 dB. The red, green, blue channel gain

for white point adjustment takes place via the bus.

The red and green DC levels for black point adjust-

ment takes place via the bus.

The PAL/SECAM matrix is provided and a specific

NTSC matrix is used when demodulation angles

are (0°,104°).

Bus-controlled Contrast and Saturation

The Contrast Control regulates internal RGB, ex-

ternal RGB and OSD RGB inputs. The maximum

attenuation on internal and external RGB inputs is

-24 dB and is limited to -12 dB for OSD RGB in-

puts. The bus-controlled saturation range is 50 dB.

Bus-controlled Brightness and Sharpness

The total brightness range is 60% of the black-to-

white amplitude at maximum contrast. The bright-

ness control regulates all RGB sources (internal,

external and OSD). Bus-controlled Sharpness

(peaking)

provided

PAL/SECAM/NTSC

standards.

Bus-controlled Coring function on Sharpness

When

the

Coring-on-sharpness

function

switched ON, the peaking function is not active on

low amplitude signals (below 10 IRE).

The Black Stretch circuit can be disabled via the

bus. Two modes are provided, one to be used

when the video signal is transmitted with a set-up

(7.5IRE set-up in NTSC), the other to be used

when the video signal is transmitted without a set-

up (PAL/SECAM).

The bus-controlled Blue Screen feature is used to

insert a blue background on the screen when no

video is available. The RGB OSD can be dis-

played when the blue screen is active.

The APR (Automatic RGB Peak Regulation) func-

tion is used to take advantage of the total RGB

output range. APR circuits detect the peak level of

the RGB outputs (before OSD insertion) and regu-

late the RGB gain (contrast) so that signals above

the APR threshold are limited. For example, at

maximum drive and contrast levels with the APR

function switched OFF, the 100 IRE input signal

gives 3 V(B/W) to the RGB outputs. With APR ON

and the APR threshold at 70 IRE, the 70 IRE input

signal gives 3 V (B/W) at RGB outputs. For input

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