FUNCTIONAL DESCRIPTION

DEFLECTION

Synchronization Separator

The synchronization separator is based on the

bottom of synchronization pulses alignment to an

internal reference voltage. An external capacitor

permits to align synchro. pulses, two external resis-

tors determines the detection threshold of synchro

pulses. The frame synchronization pulses are

locked to a 32

µs reference signal to perfect inter-

lacing.

Horizontal Scanning

The horizontal scanning frequency is obtained from

a 500kHz VCO. The circuit uses two phase-locked

loops (PLL). The first one controls the frequency;

the second one, fully integrated, controls the rela-

tive phase of the synchronization and the line fly-

back signals.

The first PLL has two times constants : a long time

constant during the picture to have a good noise

immunity, a short time constant at the beginning of

the frame to recapture faster the phase in case of

VCR video signal. More over, the PLL is in short

time constant three lines before frame pulses oc-

cured, it permits to ensure good interlacing when

the video signal comes from a VCR tape with high

phase error.

The horizontal output signal is 28

µs width. On

starting up, horizontal pulses are enabled at

The vertical output signal is 10.5 lines width. It

permits to drive a sawtooth generator such as

TDA1771.

A video recognition function permits to sent the

information of no video identification to SAT pin : it

forces a low level when no video detection occurs.

CHROMA

ACC Amplifier, DL Matrix and Demodulator

The correct chroma subcarrier input, issued from

bandpass, is internally selected with the standard.

The ACC amplifier envolves three stages : the first

one select the correct input, the second one the

-6dB in picture (PAL mode), the third one is con-

troled by the ACC voltage.

The dynamic range is over than 30dB.

The chrominance output signal is fed to the delay

line.

The adding and substracting direct and delayed

signals are performed by the DL matrix function.

Two

synchronous

demodulators

multiplies

the (B-Y) signal with the 0 degree phase 4.43MHz

reference signal and the (R-Y) signal with the alter-

nate

± 90 deg. 4.43MHz phase reference signal.

4.43MHz Phase Locked Loop

The oscillating frequency of the 4.43MHz crystal

oscillator is controlled by the output voltage of the

loop filter. The phase detector will lock the 90 de-

gree reference signal to the direct burst signal.

A 90 degree phase shifter permits to recover the

0 degree reference signal. A flip-flop driven by line

pulses permits to generate the alternate

± 90 de-

gree signal.

ACC Control and Color Killer

The direct burst signal is demodulatedwith the

± 90

degree reference signal. The demodulation result

is used by ACC control and killer function.

If the demodulation result is always positive, the

killer capacitor is charged and the standard is iden-

tified (color ON). When demodulation result is al-

ways negative, the killer capacitor voltage reaches

the flip-flop inhibition level, so the alternace se-

quence is reversed and the capacitor is charged

again.

In case of no video signal, the killer capacitor

off threshold.

VIDEO

The luminance input is controlled by the contrast

control stage which range is 20dB.

The luminance and color difference signals are

added in the video matrix circuit to obtain the color

signals.

The color signals are sent to an RGB switch which

will drive to the outputs either internal RGB signals

or external RGB signals.

Automatic Cut-off Control

The black levels of the RGB outputs are controlled

with the cut-off loops during three line periods after

the frame retrace. The cut-off measurements are

sequentially achieved during these three lines. The

leakage current measurement is achieved during

the frame retrace and memorized on an internal

capacitor, thus the circuit is able to extract the

cut-off current from the total current measurement.

Warm-up Detector

At the start-up, the cut-off loops are switch off, a

white level is inserted on the luminance signal until

a cathode current is detected. Then the cut-off

loops are released.

STV2102

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