EL4581C Elantec Semiconductor, Inc. (acquired by Intersil), EL4581C Datasheet - Page 9

• Manufacturer Part Number: EL4581C
• Description: Video SYNC Separator
• Manufacturer: Elantec Semiconductor, Inc. (acquired by Intersil)

Description of Operation
vertical sync pulse widths The internal timing
circuits are referenced to I
out period being inversely proportional to the
timing current The vertical output pulse is start-
ed on the first serration pulse in the vertical in-
terval and is then self-timed out In the absense
of a serration pulse an internal timer will default
the start of vertical
The back porch is triggered from the sync tip
trailing edge and initiates a one-shot pulse The
period of this pulse is again a function of I
will therefore track the scan rate set by RSET
Block Diagram
Note RSET must be a 1% resistor
OT
and V
R3
Contd
the time-
Sync Separator 50% Slice S-H Filter
OT
and
Figure 5
9
The odd even circuit (O E) comprises of flip
flops which track the relationship of the horizon-
tal pulses to the leading edge of the vertical out-
put and will switch on every field at the start of
vertical Pin 7 is high during the odd field
Loss of video signal can be detected by monitor-
ing the C S output The 50% level of the previ-
ous video signal will remain held on the S H ca-
pacitors after the input video signal has gone and
the input on pin 2 has defaulted to the clamp
voltage Consequently the C S output will re-
main low longer than the normal vertical pulse
period An external timing circuit could be used
to detect this condition
EL4581C
4581 – 4