Splitting sync-on-green video signal

How though would one determine the propagation delay?

Start by separating out a logic signal for 'sync'; a one-transistor amplifier, with the base DC bias set by the average collector voltage, will work. You know the sync duty cycle, just ground an NPN's emitter, put a pullup resistor to +5 on the collector, and AC-couple the video to the base, DC-couple a divided-down collector voltage to the base.

Now run two PLLs on the sync signal, one for H, one for V.

Finally, use a video buffer amplifier biased to clip the low SYNC level but still have unity gain for the video signal range; it's do-able.

Standard trick in the (old) digital days was to run both signals through similar gates.

For example if you wanted to gate a clock pulse, you ran it through a x00. You also ran all the other clocks (that were supposed to happen at the same time) through a similar gate.

First chioice was to put all the related gates in the same chip.

Second choice was to use the same type of chip.

Third choice was to use a handy gate of the same logic family.

ed

Um, you measure it with a scope and a test pattern that has white (R/G/ B) vertical lines and measure the delay. You can easily get to under a nanosecond with a good scope. The delay in the green processing can be made up by shortening the cable. Any decent analog video guy can do that.

G=B2

Recover the separate sync and leave the green plus sync alone. It is NOT= =20 during displayable time; it is "blacker than black" (gun cutoff). It is=20 not visible and will not hurt the monitor.