AD9983A datasheet(17/44 Pages) AD

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AD9983A

Rev. 0 | Page 17 of 44

HSYNCOUT

VSYNC

FILTER

WINDOW

EXPECTED

EDGE

FILTER

WINDOW

EQUALIZATION

PULSES

HSYNCIN

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

HSYNCIN

VSYNCIN

VSYNCOUT

O/E FIELD

ODD FIELD

QUADRANT

Figure 11. Vsync Filter—Odd Field

FIELD 1

FIELD 0

SYNC SEPARATOR THRESHOLD

FIELD 1

FIELD 0

HSYNCIN

VSYNCIN

VSYNCOUT

O/E FIELD

EVEN FIELD

QUADRANT

Figure 12. Vsync Filter—Even Field

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