AD9923 Analog Devices, AD9923 Datasheet - Page 17

• Manufacturer Part Number: AD9923
• Manufacturer: Analog Devices

Sync Slicer
The purpose of the sync slicer is to extract the sync signal from
the green graphics or luminance video signal that is connected
to the SOGIN input. The sync signal is extracted in a two step
process. First, the SOG input (typically 0.3 V below the black
level) is detected and clamped to a known dc voltage. Next, the
HSYNC 0
HSYNC 1
VSYNC 0
VSYNC 1
SOGIN 0
SOGIN 1
COAST
SOGOUT OUTPUT
CONNECTED TO
1
2
3
4
5
ACTIVITY DETECT
POLARITY DETECT
REGENERATED HSYNC
FILTERED HSYNC
SET POLARITY
SEPARATOR
AT HSYNCIN
COMPOSITE
FROM SYNC
VSYNCOUT
SOG INPUT
AD
AD
AD
AD
HSYNCIN
1
1
1
1
SYNC
SLICER
700mV MAXIMUM
SLICER
SYNC
SYNC
AD9880
–300mV
–300mV
PD
PD
AD
AD
PD 2
PD 2
0mV
2
2
1
1
MUX
MUX
MUX
FILTER COAST VSYNC
CHANNEL
SELECT
VSYNC
0x12:0
NEGATIVE PULSE WIDTH = 40 SAMPLE CLOCKS
Figure 9. Sync Slicer and Sync Separator Output
Figure 8. Sync Processing Block Diagram
[0x11:3]
VSYNC FILTER
PROCESSOR
SYNC
Rev. 0 | Page 17 of 64
AND
COAST SELECT
0x12:1
MUX
HSYNC
SELECT
MUX
PLL SYNC FILTER EN
COAST
SP SYNC FILTER EN
0x21:6
signal is routed to a comparator with a variable trigger level (set
by Register 0x1D, Bits [7:3]), but nominally 0.128 V above the
clamped voltage. The sync slicer output is a digital composite
sync signal containing both Hsync and Vsync information (see
Figure 9).
[0x11:7]
MUX
0x21:7
HSYNC
GENERATOR
PLL CLOCK
MUX
FH 4
REGENERATOR
HSYNC FILTER
HSYNC/VSYNC
AND
REG 26H, 27H
COUNTER
RH 3
SOGOUT SELECT
FILTERED
VSYNC
MUX
0x24:2,1
VSYNC
VSYNC FILTER EN
SP
SP
5
5
SP
0x21:5
MUX
SP
5
5
SOG OUT
VSYNC OUT
ODD/EVEN
FIELD
HSYNC OUT
DATACK
AD9880