SNLS384F – FEBRUARY 1995 – REVISED MARCH 2013
Instead of using the vertical serration pulse separation, use the actual pulse width of the vertical sync period, or
64 µs in this example. This graph is linear, meaning that a value as large as 2.7 MΩ can be used for R
SET
(twice
the value as the maximum at 30 µs). Due to leakage currents it is advisable to keep the value of R
SET
under 2.0
MΩ. In this example a value of 1.0 MΩ is selected, well above the minimum of 680 kΩ. With this value for R
SET
the pulse width of the vertical sync output pulse of the LM1881 is about 340 µs.
Figure 8. (a) Composite Video; (b) Composite Sync; (c) Vertical Output Pulse;
(d) Odd/Even Field Index; (e) Burst Gate/Back Porch Clamp
6
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