How to sync to NTSC color burst (3.58MHz sine wave that only lasts for 9 cycles every 63 microseconds)

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mpownby

Joined Oct 7, 2016
14
I need a digital clock (ie square wave) that is in sync with the color burst (3.58 MHz sine wave) from an NTSC composite signal (see attached picture). One challenge is that this sine wave is only present for about 9 cycles every 63 microseconds, due to the way NTSC is designed. I need to be able to refer to this clock at any time, not just while the color burst is active. I know that this is a solvable problem since every analog TV set has an internal circuit to solve this problem. Unfortunately, I've had a very difficult time finding answers by googling, partly because most of the resources I find seem to assume some basic knowledge that I lack.

I've already determined that an LM1881 can help with this as it will indicate approximately when the color burst is active. I also assume that I will need some kind of phase locked loop, but I'm not sure how to take advantage of this, since it's my understanding that every PLL has some delay relative to the original clock it is mimicking (how to compensate for the delay?). I'm also not sure how to detect the difference between the sine wave itself and just random analog noise.

I've bought a few books on basic analog electronics, and am willing to do some reading, but I could use some pointers in the right direction to help me focus.

Any help is appreciated.
 

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MrChips

Joined Oct 2, 2009
26,480
You need a PLL built around a 3.579545MHz color burst crystal oscillator.
The PLL will lock on to the phase of the incoming color burst and will stay in phase until the next color burst signal is received 63μs later.

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