Datasheet
AD9984A
Rev. 0 | Page 16 of 44
SYNC PROCESSING
The inputs of the sync processing section of the AD9984A are
combinations of digital Hsyncs and Vsyncs, analog sync-on-
green or sync-on-Y signals, and an optional external coast
signal. From these signals, the part generates a precise, jitter-
free clock from its PLL, an odd/even-field signal, HSOUT and
VSOUT signals, a count of Hsyncs per Vsync, and a
programmable SOGOUT. 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 SOGINx inputs, and outputs a digital composite sync.
• The sync separator extracts Vsync from the composite sync
signal, which can come from either the sync slicer or the
HSYNCx inputs.
• The Hsync filter is used to eliminate any extraneous pulses
from the HSYNCx or SOGINx 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 counting Hsyncs per Vsync.
• The Vsync filter is used to eliminate spurious Vsyncs, main-
tain 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 to allow the
PLL to maintain its frequency in the absence of Hsync pulses.
AD9984A
SOGOUT
HSYNC
VSYNC
COAST
COAST SELECT
0x18:7
DATACK
SOGIN0
EXTCK/COAST
VSYNC1
MUX
MUX
MUX
MUX
MUX
MUX
MUX
MUX
VSYNC0
HSYNC1
HSYNC0
HSOUT
VSOUT/A0
SOGIN1
HSYNC
SELECT
0x12:6
FILTERED
HSYNC
ACTIVITY
DETECT
ACTIVITY
DETECT
ACTIVITY
DETECT
ACTIVITY
DETECT
ACTIVITY
DETECT
ACTIVITY
DETECT
POLARITY
DETECT
POLARITY
DETECT
POLARITY
DETECT
POLARITY
DETECT
SYNC SLICER
SYNC SLICER
PLL CLOCK
GENERATOR
O/E FIELD
CHANNEL
SELECT
0x1E:6
HSYNC FILTER
AND
REGENERATOR
REGENERATED
HSYNC
SET
POLARITY
SYNC PROCESSOR
AND VSYNC FILTER
06476-008
SET
POLARITY
HSYNC/VSYNC
COUNTER
REG 0x26,
0x27
SET
POLARITY
SET
POLARITY
VSYNC
FILTERED VSYNC
VSYNC FILTER EN
0x14:2
VSYNC
FILTER EN
0x14:2
PLL SYNC
FILTER EN
0x20:2
SP SYNC
FILTER EN
0x20:1
SOGOUT
SELECT
0x1D:1,0
MUX
Figure 9. Sync Processing Block Diagram