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The general NTSC waveform and its attributes

       A video signal contains many kinds of information. There is sync information that tells the scan circuits of a monitor when to start a new line or field. There is the video portion that conveys brightness, as well as color, information. Another kind of information you can sometimes find in a video signal is closed captioning and or digital data that can be hitchhiking in the vertical blanking region of the TV signal.

       The video signal uses voltage to create an analog of the original light information at that point in space and time. The standard convention is that zero volts represents black and approximately plus point seven volts is peak white. (0V - 0.714V - more on that shortly) In the case of a color TV signal, there can be an RF carrier present on the video as well. I will not go into that as none of my circuits deal directly with the color signal at this time.

       Synchronizing information is represented by the pulses that go negative below the blanking level. This diagram only shows horiontal sync information. Vertical sync will be covered later when it becomes pertinent. Note the timing between the sync pulses and blanking intervals. I will show you circuits that are dependant on these numbers for specific sync funtions. DC restoration, for instance.

       Take note of the IRE levels on the diagram. An IRE unit is 1 volt, divided by one hundred forty. One IRE unit equals 714.3 millivolts. Sync extends from zero IRE, the video blanking level which is also zero volts DC, to -40 IRE units, or -0.286V. The video information goes from zero IRE to 100 IRE units, or 0.714V.

       I am covering this topic very lightly, highlighting the parts that apply to the circuits in the Video Circuits Cook Book. The following links will direct you to more detailed discussions of the topic. Read more about [NTSC], [PAL] and [SECAM] composite video signals on Wikipedia.