AD9983A
Rev. 0 | Page 15 of 44
AD9983A
SOGOUT
HSYNC
COAST
DATACK
SOGIN0
EXTCK/COAST
VSYNC1
MUX
VSYNC0
HSYNC1
HSYNC0
HSOUT
VSOUT/A0
SOGIN1
HSYNC
SELECT
FILTERED
HSYNC
ACTIVITY
DETECT
ACTIVITY
DETECT
ACTIVITY
DETECT
ACTIVITY
DETECT
ACTIVITY
DETECT
ACTIVITY
DETECT
POLARITY
DETECT
POLARITY
DETECT
POLARITY
DETECT
POLARITY
DETECT
SYNC SLICER
PLL CLOCK
GENERATOR
O/E FIELD
CHANNEL
SELECT
HSYNC FILTER
AND
REGENERATOR
REGENERATED
HSYNC
SET
POLARITY
SYNC
PROCESSOR
AND
VSYNC FILTER
HSYNC/VSYNC
COUNTER
REG 0x26, 0x27
0
64
75
-01
3
SET
POLARITY
SET
POLARITY
SET
POLARITY
Figure 8. Sync Processing Block Diagram
SYNC PROCESSING
The inputs of the sync processing section of the AD9983A 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 it 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 input and outputs a digital composite sync.
The sync separator’s task is to extract 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,
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.
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 SOG input. The sync signal is extracted in a two step
process. First, the SOG input is clamped to its negative peak,
(typically 0.3 V below the black level). Next, the signal goes to a
comparator with a variable trigger level (set by Register 0x1D,
Bits[7:3]), but nominally 0.128 V above the clamped level. The
sync slicer output is a digital composite sync signal containing
both Hsync and Vsync information (see
Figure 9).