AD9923 Analog Devices, AD9923 Datasheet - Page 19

• Manufacturer Part Number: AD9923
• Manufacturer: Analog Devices

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.
HSYNCOUT
HSYNCIN
WINDOW
FILTER
VSYNC
Figure 10. Sync Processing Filter
Rev. 0 | Page 19 of 64
WINDOW
FILTER
QUADRANT
QUADRANT
VSYNCOUT
VSYNCOUT
O/E FIELD
O/E FIELD
HSYNCIN
HSYNCIN
VSYNCIN
VSYNCIN
EXPECTED
EDGE
2
2
FIELD 1
FIELD 1
SYNC SEPARATOR THRESHOLD
EQUALIZATION
Figure 12. Vsync Filter—Odd/Even
3
3
PULSES
4
4
SYNC SEPARATOR THRESHOLD
FIELD 0
FIELD 0
Figure 11.
EVEN FIELD
ODD FIELD
1
1
2
2
FIELD 1
FIELD 1
3
3
4
4
AD9880
FIELD 0
FIELD 0
1
1