Datasheet

AD9983A
Rev. 0 | Page 17 of 44
HSYNCOUT
VSYNC
FILTER
WINDOW
EXPECTED
EDGE
FILTER
WINDOW
EQUALIZATION
PULSES
HSYNCIN
06475-016
Figure 10. 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 11 and Figure 12
illustrate even/odd field determination in two situations.
FIELD 1 FIELD 0
SYNC SEPARATOR THRESHOLD
FIELD 1 FIELD 0
23 214431
HSYNCIN
VSYNCIN
VSYNCOUT
O/E FIELD
ODD FIELD
QUADRANT
06475-017
Figure 11. Vsync Filter—Odd Field
FIELD 1 FIELD 0
SYNC SEPARATOR THRESHOLD
FIELD 1 FIELD 0
23 214431
HSYNCIN
VSYNCIN
VSYNCOUT
O/E FIELD
EVEN FIELD
QUADRANT
06475-018
Figure 12. Vsync Filter—Even Field