ST92195D datasheet(146/249 Pages) STMICROELECTRONICS

146 / 249 page

146/249

ST92195C/D - SYNC EXTRACTOR

7.6 SYNC EXTRACTOR

The Sync Extractor extracts the Sync pulses from

the CVBS signal and determines the CVBS

HSYNC and VSYNC signals. The CVBS HSYNC

signal is fed to the VPS/WSS slicer and to the

Teletext Slicing Unit to re-synchronize them at

each TV line.

The Sync Extractor Unit provides the CVBS

VSYNC pulse to the Csync Controller unit which

might use it for some standalone modes when the

chassis time base is switched off (refer to the Sync

Controller chapter for more details).

7.6.1 Time Windowing For Slicers

A line counter counts the CVBS HSYNC pulses in

order to open and close the proper windows within

each field for slicing the Teletext (lines 6 to 22 for

the first field, lines 318 to 335 for the second field),

VPS (lines 15 to 17) or WSS (lines 22 to 24) data.

The line counter is able to count a complete field

before overflowing.

An extended Teletext Search window can be pro-

grammed by software through the TXTES bit of

the Teletext Slicer Control register (TXSCR) (refer

to the Teletext Slicing Unit chapter). The extended

window starts at line 2 (first field) or line 315 (sec-

ond field).

7.6.2 Field Detection

To secure the slicing units functionality, a field de-

tection is implemented. This field detection flag is

updated at each beginning of field. In case a field

start is missed, the field detection flag will keep

toggling according to its previous value and the

end of field predicted by the line counter (312 or

313 lines).

7.6.3 CVBS Amplitude Information

The Sync Extractor unit provides information

about the real time amplitude of the CVBS signal.

This information is obtained by storing the peak

value of the sync pulse referred to the black level.

This analog voltage is bufferized and forwarded to

the on-chip A/D Converter.

7.6.4 CVBS Signal Quality

The quality of the CVBS Sync pulses is also

checked by the Sync Extractor according to the

following criteria: a TV line is declared “bad” if two

or more HSYNC pulses are found within 64 µs, or

if the HSYNC pulse is missing. Each time a “bad”

TV line is detected, a “Bad TV line” pulse is for-

warded to the Acquisition which is part of the Tele-

text Slicing Unit. These pulses are counted only

during the Vertical Blank Interval, providing a qual-

ity criterion of the CVBS signal at the time the slic-

ers treat it. For more details on the subject, refer to

the Teletext Slicing.

7.6.5 Sync Extractor Switch Off

When the VPS/WSS and Teletext slicers are

switched off, the Sync Extractor automatically en-

ters an idle state to prevent current consumption.

Figure 86. Time Windowing for Slicers

CVBS1

SYNC Extractor

Analog

Front-End

Digital

Filtering

Hcvbs (to Slicers, Sync. Controller, VPS/WSS PLL.)

Vcvbs (to Slicers, Sync. Controller)

Bad TV Line (to Acquisition Unit)

Teletext Extended Search Window

Teletext Search Window

VPS Search Window

VSS Search Window

VDETB/VBGP (to A/D Converter, Channel 0)

ST92195D Datasheet(PDF) 146 Page - STMicroelectronics

ST92195D Datasheet(HTML) 146 Page - STMicroelectronics

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 ...More

Datasheet Download

Link URL