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TEA5040S

WIDE BAND VIDEO PROCESSOR

STMicroelectronics 

TEA5040S

pulse. Since this integrated circuit can be directly

connected to two different sources, it is necessary

then to have two separate insertion pulse inputs

(pin 8-9). Fast blanking can be inhibited by a one

active bit word. The two fast blanking inputs carry

out an OR function to insert R, G, B sources into

TV picture. The external fast blanking (FB ext.)

selects the appropriate R, G, B source.

Controls

The four brightness, contrast and saturation control

functions are direct digitally controlled without us-

ing digital-to-analog converters.

The contrast control of the Y channel is obtained

by means of a digital potentiometer which is an

attenuator including several switchable cells di-

rectly controlled by a 5 active bit word (address

number 1). The brightness control is also made by

a digital potentiometer (5 active bit word, address

number 0). Since a + 3dB contrast capability is

required, the Y signal value could be up to 0.7Vpp

nominal. For both functions, the control charac-

teristics are quasi-linear.

In each R-Y and B-Y channel, a six-cell digital

attenuator is directly controlled by a 6 active bit

word (address number 6 and 7). The tracking

neede d to keep the saturation constant when

changing the contrast has to be done externally by

the microcontroller. Furthermore, colour can be

disabled by blankingR-Y and B-Y signals using one

active bit word (address number 2) to drive the

one-chip colour ON/OFF switch.

Second Matrix, Clamp, Peak Clipping, Blank-

ing

The second matrix receives the Y, R-Y and B-Y

signals and delivers the corresponding R, G, B

signals. As it is required to have the capability of +

6dB saturation, an internal gain of 2 is applied on

both R-Y and B-Y signals.

A low clipping level is included in order to ensure a

correct blanking during the line and frame retraces.

A high clipping level ensures the peak beam current

limitation. These limitations are correct only if the

DC bias of the three R, G, B signals are precise

enough. Therefore a clamp has been added in

each channel in order to compensate for the inac-

curacy of the matrix.

Sandcastle Detector And Counter

The three level supersandcastle is used in the

circuit to deliver the burst pulse (CLP), the horizon-

tal pulse (HP), and the composite vertical and

horizontal blanking pulse (BLI). This last one is

regenerated in the counter which delivers a new

4/12

composite pulse (BL) in which the vertical part lasts

23 lines when the vertical part of the supersand-

castle lasts more than 11 lines.

The TEA5040S cannot work properly if this mini-

mum duration of 11 lines is not ensured.

The counterdelivers different pulses neededcircuit

and especially the line pulses 17 to 23 used in the

automatic drive and cut-off control system.

Automatic Drive And Cut-off Control System

Cut-off and drive adjustments are no longer re-

quired with this integrated circuit as it has a sample

and hold feedback loop incorporating the final

stages of the TV-set. This system works in a se-

quential mode. For this purpose, special pulses are

inserted in G, R and B channels. During the lines

17, 18 and 19, a ”drive pulse” is inserted respec-

tively in the green, red and blue channels. The line

20 is blanked on the three channels. During the

lines 21, 22 and 23, a ”quasi cut-off pulse” is

inserted respectively in the green, red and blue

guns.

The resulting signal is then applied to the input of

a voltage controlled amplifier. In the final stages of

the TV-set, the current flowing in each green, red

and blue cathode is measured and sent to the

videoprocessor by a current source.

The three currents are added together in a resistor

matrix which can be programmed to set the ratio

between the three currents in order to get the

appropriate colour temperature. The output of the

matrix forms a high impedance voltage source

which is connected to the integratedcircuit (pin 34).

Same measurement range between drive and cut-

off is achieved by internally grounding an external

low impedance resistor during lines 17, 18 and 19.

This is due to the fact that the drive currents are

about one hundred times higher than the cut-off

and leakage currents.

Each voltage appearing sequentially on the wire

pin 34 is then a function of specific cathode cur-

rent :

- When a current due to a drive pulse occurs, the

voltage appearing on the pin 34 is compared

within the IC with an internal reference, and the

result of the comparison charges or discharges

an external appropriate drive capacitor which

stores the value during the frame. This voltage is

applied to a voltage controlled amplifier and the

system works in such a way that the pulse current

drive derived from the cathode is kept constant.

- During the line 20, the three guns of the picture

tube are blanked. The leakage current flowing out

of the final stages is transformed into a voltage

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