Analog Devices AD9380 Manual page 17

Sync Processing
The inputs of the AD9380 sync processing section are
combinations of digital HSYNCs and VSYNCs, analog sync-on-
green signal, sync-on-Y signal, and an optional external coast
signal. From these signals, the AD9380 generates a precise,
jitter-free (9% or less at 95 MHz) clock from its PLL; an
odd/even field signal; HSYNC and VSYNC out signals; a count
of HSYNCs per VSYNC; and a programmable SOG output. The
main sync processing blocks are the sync slicer, sync separator,
HSYNC filter, HSYNC regenerator, VSYNC filter, and coast
generator.
The sync slicer extracts the sync signal from the green graphics
or luminance video signal that is connected to the SOGIN input
and outputs a digital composite sync. The sync separator's task
HSYNC 0
1
AD
HSYNC 1
1
AD
SOGIN 0 www.BDTIC.com/ADI
SLICER
SYNC
SOGIN 1
SLICER
VSYNC 0
1
AD
VSYNC 1
1
AD
COAST
1
ACTIVITY DETECT
2
POLARITY DETECT
3
REGENERATED HSYNC
4
FILTERED HSYNC
5
SET POLARITY
CHANNEL
SELECT
MUX
2
PD
2
PD
SYNC
MUX
1
AD
1
AD
VSYNC
MUX
2
PD
2
PD
FILTER COAST VSYNC
0x12:0
AD9380
Figure 8. Sync Processing Block Diagram
is to extract VSYNC from the composite sync signal, which can
come from either the sync slicer or the HSYNC input. The
HSYNC filter is used to eliminate any extraneous pulses from
the HSYNC or SOGIN inputs, outputting a clean, low jitter
signal that is appropriate for mode detection and clock
generation. The HSYNC regenerator is used to recreate a clean,
although not low jitter, HSYNC signal that can be used for
mode detection and for counting HSYNCs per VSYNC. The
VSYNC filter is used to eliminate spurious VSYNCs, maintain a
stable timing relationship between the VSYNC and HSYNC
output signals, and generate the odd/even field output. The
coast generator creates a robust coast signal that allows the PLL
to maintain its frequency in the absence of HSYNC pulses.
HSYNC
[0x11:3]
[0x11:7]
SELECT
MUX
SP SYNC FILTER EN
0x21:7
SYNC
MUX
PROCESSOR
AND
VSYNC FILTER
PLL SYNC FILTER EN
0x21:6
HSYNC
COAST
PLL CLOCK
MUX
GENERATOR
COAST SELECT
0x12:1
Rev. 0 | Page 17 of 60
HSYNC FILTER
AND
REGENERATOR
3
4 RH
FH
MUX
5
SP
SOGOUT SELECT
0x24:2,1
VSYNC
FILTERED
MUX
VSYNC
VSYNC FILTER EN
0x21:5
HSYNC/VSYNC
COUNTER 5
SP
REG 26H, 27H
MUX
5
SP
5
SP
AD9380
SOGOUT
VSOUT
O/E
FIELD
HSOUT
DATACK