AD9880SLASHPCB datasheet(19/64 Pages) AD

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AD9880

Rev. 0 | Page 19 of 64

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 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

HSYNCIN

VSYNCIN

VSYNCOUT

O/E FIELD

EVEN FIELD

QUADRANT

Figure 11.

FIELD 1

FIELD 0

SYNC SEPARATOR THRESHOLD

FIELD 1

FIELD 0

HSYNCIN

VSYNCIN

VSYNCOUT

O/E FIELD

ODD FIELD

QUADRANT

Figure 12. Vsync Filter—Odd/Even

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