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STV2112B

BUS-CONTROLLED PAL/SECAM TV PROCESSOR

STMicroelectronics 

STV2112B

FUNCTIONAL DESCRIPTION

1 - DEFLECTION CIRCUIT

Note : [X,Y] : line number referred to the internal

line counter numbering

- Fully integrated synch. separator, with a low pass

filter, a black level alignment of the Y/CVBS input, a

slicing level at 2/3,1/3of the sync. pulse amplitude.

- Frame sync. pulse locked on 2 fH frequency to

perfect interlace.

- 500kHz VCO with an externalceramic resonator.

- Two phase locked loops

• the first PLL locks the VCO on the video signal

frequency,

• the second PLL compensates the line transistor

storage time.

- Three time constants for the first PLL.

• thelong timeconstantis usedfor normaloperation

• the short time constant is automatically used

during the frame retrace and in search mode of

VCR when the frame pulse is outside [258,264]

and [309,314].

• very long time constant when no video recognition

Time constants in normal operation

(automatic selection of time constants) :

50Hz input signal :

- short time constant : [306, 21]

- long time constant : the rest of the field

• inhibition of the first PLL :

the first locked loop is opened from line 309 to

line 4.5 (or 314) in 50Hz mode.

• the time constantsvalues are chosenby means

of external components.

• possibility to force the short time constant

through the bus.

• possibility to force the very long time constant

through the bus.

- Video identification : coincidence detector be-

tween the line synchro top and a line frequency

window from the firstPLL. The video identification

status is available in the output register of the I2C

bus decoder.

- Generation of burst gate pulses and line fre-

quency signals from the first PLL to drive the

chroma and video circuits. The burst gate pulse

is also sent to the sandcastle generator.

- Frame synchro window :

[248, 352] catching

- Field frequency selection windows :

[288, 352] 50Hz mode selection window

- frame blanking pulse :

from line 0 to 21 in 50Hz mode

- Vertical output pulse is 10.5 lines long.

- Horizontal output pulse : 28µs line pulse on an

open collector output;

- Start up circuit : the horizontal output is at a high

level when VCC increases from 0 to 6.8V. On

shutting down, horizontal pulses are disabled

when VCC is below 6.2V.

- Soft-start circuit : the duty cycle of the horizontal

output is 78 % (Thigh/(Thigh + TLow))when VCC1

is lower than (0.75 x VCC2), during the rising time.

During the falling time, a 78% duty cycle HOUT

pulse is provided when VCC1 is lower than

(0.60 x VCC2).

- Possibility to disable the horizontal output pulse

through the bus (force a high level on HOUT).

- Horizontal position adjustment controlled by bus.

- Bus controlledoutput voltage to adjustthe vertical

amplitude ; this voltagepermitsto adjustthe slope

of the vertical sawtooth generated by the external

frame booster.

- Bus controlled vertical position ; the high level of

the vertical pulse permits to adjust the vertical

position.

- Bus controlled 4/3-16/9 selection : the low level

of the vertical pulse is 0.1V when 16/9 is selected,

2V when 4/3 is selected.

- Combined flyback input and sandcastle output

(Pin 37). Two thresholds on LFB/SCO Pin : The

lowest threshold (0.7V) permits to extract the line

blanking pulse ; the highest threshold (2V) per-

mits to extract the line pulse for PLL2. The sand-

castle signal at Pin 37 is used to control the

external baseband chroma delay line.

2 - FILTERS

- Integrated trap filter :

Q

=

fo

f−3dB

1

−

f−3dB

fo

Q = 1.7 at sharp. min

Q = 3.0 at sharp. max

Center frequency :

- 4.43MHz for PAL

- 4.25MHz, for SECAM (f-3dB = 3MHz; -20dB

rejection between 4.1MHz and 4.4MHz)

- Integrated chroma bandpass :

Q = 3.5, Center frequency= 4.43MHz

- Integrated cloche filter for SECAM :

Q = 16, Center frequency = 4.286MHz

- Integrated delay line : Bandwidth = 8MHz

- Integrated low pass filter for deflection part.

- Allfilters aretunedwitha referencephaselockedloop.

The PLL consists ofa lowpass filter, a phasecompa-

rator,a loopfilter (with an externalcapacitor).The ref-

erence signal is the continuouscarrier wave from the

VCO (4.43MHz). The PLL adjusts the center fre-

quency of the lowpass so that it is equal to the

referencesignal.The tuningvoltageof the PLLis used

to adjust all otherfilters. The cloche filter is fine tuned

with a secondPLLoperatingduring frame retrace.

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