STV2000 datasheet(26/38 Pages) STMICROELECTRONICS

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STV2000

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OPERATING DESCRIPTION (continued)

Figure 16.

1.4 Brightness Adjustment (6 bits)

As with contrast adjustment, brightness is control-

led by I2C.

The brightness function consists of adding the

same DC offset to the three R, G, B signals after

contrast amplification. This DC-Offset is present

only outside the blanking pulse (see Figure 18).

The DC output level is forced to ”INFRA-BLACK”

level (VDC) during the blanking pulse.

1.5 Drive Adjustment (3 x 8 bits)

To adjust the white balance, the device offers the

possibility of separately adjusting the overall gain

of each complete video channel. Each channel

gain is controlled by I2C (8 bits each). The very

large drive adjustment range (48dB) allows differ-

ent standard or custom color temperatures.

The drive adjustment is also used to adjust the

output voltages at the optimum amplitude to drive

the C.R.T drivers, keeping the whole contrast con-

trol for end-users only. The drive adjustment is

made after the contrast and brightness so that the

white balance remains correct when BRT is ad-

justed.

1.6 Output Stage

The three output stages (see Figure 17) incorpo-

rate three functions:

• The blanking stage: when the internal

generated blanking pulse is high, the three

outputs are switched to a voltage which is

400 mV

lower than the BLACK level. The

black level is the output voltage with minimum

brightness

when

the

input

signal

video

amplitude is equal to ”0”.

• The output stage itself: a large bandwidth

output amplifier which can deliver up to 5VPP

on the three outputs (for 0.7 V video signal on

the inputs).

• The output CLAMP: the IC also incorporates

three internal output clamps (sample and hold

system) used for the DC to shift the three

output signals. The DC output voltage is fixed

at 1.5 V.

The overall waveforms of the output signal accord-

ing to the different adjustments are shown in

Figure 18.and Figure 19.

Figure 17.

-2

-4

-6

-8

-10

-12

-14

Attenuation (dB)

(V)

CRT Driver

STV2000

Vout

1.5V

S/H

Cut-off

DAC

8 bits

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