GS1881_09 Datasheet, PDF (17/29 Pages) Gennum Corporation – Monolithic Video Sync Separators

4.5 Horizontal Output (Pin 7 GS4981)
As mentioned above, the odd/even field output of the GS1881 and GS4881 is generated
by comparing vertical sync with an internal horizontal sync signal. This horizontal sync
signal is a true horizontal signal (i.e. maintained during the vertical interval) and is
outputted on Pin 7 for the GS4981. A delay of 190ns from the video input and a width of
6.5μs are typically characteristics for this signal. The windowing circuit which generates
horizontal provides excellent impulse noise immunity as shown in Figure 4-4. This
output buffer is an open collector stage with an internal 10kΩ pull up resistor.
Video
Input
Horizontal
Output
Impulse
Noise
Figure 4-4: Horizontal Output
4.6 Block Diagrams
VIDEO
INPUT
-
(Pin 2)
+
-
V SLICE ⁺
-
V CLAMP ⁺
C SYNC
11μ
85μ
V_CC
(Pin 8)
R_SET
(Pin 6)
VOLTAGE
REGULATOR
1.2V
TIMING
CURRENTS
Figure 4-5: GS1881 Block Diagram
GS1881, GS4881, GS4981 Monolithic Video Sync
Separators
Data Sheet
6926 - 5
November 2009
HORIZONTAL
WINDOWING
CIRCUIT
NOSYNC
VERTICAL
DETECTOR
BACK PORCH
DETECTOR
DQ
GQ
COMPOSITE
SYNC OUTPUT
(Pin 1)
DQ
CLK Q
ODD / EVEN
OUTPUT
(Pin 7)
DQ
CLK ^Q
VERTICAL SYNC
OUTPUT
(PIN 3)
BACK PORCH
OUTPUT
(Pin 5)
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