Datasheet

AD9984A
Rev. 0 | Page 18 of 44
HSYNCOUT
VSYNC
FILTER
WINDOW
EXPECTED
EDGE
FILTER
WINDOW
EQUALIZATION
PULSES
HSYNCIN
06476-010
Figure 11. Sync Processing Filter
Vsync Filter and Odd/Even Fields
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 filter works by examining the placement of Vsync with
respect to Hsync and if necessary, shifting it in time slightly.
The goal is to keep the Vsync and Hsync leading edges from
switching at the same time, thus eliminating confusion as to
when the first line of a frame occurs. Register 0x14, Bit 2 enables
the Vsync filter. Use of the Vsync filter is recommended for all
cases, including interlaced video, and is required when using
the Hsyncs per Vsync counter.
Figure 12 and Figure 13 illustrate
even/odd field determination in two situations.
FIELD 1 FIELD 0 FIELD 1 FIELD 0
23 214431
HSYNCIN
VSYNCIN
VSYNCOUT
O/E FIELD
EVEN FIELD
QUADRANT
06476-012
SYNC SEPERATOR THRESHOLD
Figure 12. Even Field
FIELD 1 FIELD 0 FIELD 1 FIELD 0
23 214431
HSYNCIN
VSYNCIN
VSYNCOUT
O/E FIELD
ODD FIELD
QUADRANT
06476-011
SYNC SEPERATOR THRESHOLD
Figure 13. Odd Field