Datasheet

AD9880
Rev. 0 | Page 19 of 64
HSYNCOUT
VSYNC
FILTER
WINDOW
EXPECTED
EDGE
FILTER
WINDOW
EQUALIZATION
PULSES
HSYNCIN
05087-010
Figure 10. Sync Processing Filter
Vsync Filter and Odd/Even Fields
The Vsync filter is used to eliminate spurious Vsyncs, maintain
a consistent 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, slightly shifting it in time at
the VSOUT output. The goal is to keep the Vsync and Hsync
leading edges from switching at the same time, eliminating
confusion as to when the first line of a frame occurs. Enabling
the Vsync filter is done with Register 0x21[5]. Use of the Vsync
filter is recommended for all cases, including interlaced video,
and is required when using the Hsync per Vsync counter.
Figure 12 illustrates 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
EVEN FIELD
QUADRANT
05087-011
Figure 11.
FIELD 1 FIELD 0
SYNC SEPARATOR THRESHOLD
FIELD 1 FIELD 0
23 214431
HSYNCIN
VSYNCIN
VSYNCOUT
O/E FIELD
ODD FIELD
QUADRANT
05087-012
Figure 12. Vsync Filter—Odd/Even