This series of VGA video signal in RGB format compatible with PAL or NTSC standard video timings.
AD722 is very low, RGB to NTSC / PAL Encoder that converts red, green and blue color component signals into a suitable lighting (baseband amplitude) and Chrominance (subcarrier amplitude and phase) signals in accordance with either NTSC or PAL standards. Both outputs are also combined to provide a video output standard komposit.Semua output can drive 75 ohm terminated video cables directly without extra amplifiers. Chip is a very compact solution, because operates from a single +5 V
IC AD722 requires crystals: 4.43MHz for PAL and 3.58MHz for NTSC. Chip needs an external clock to operate the crystal, so the circuit provides the color subcarrier frequency crystals: 4.43MHz for PAL and NTSC 3.58MHz to.
You also need to adjust the width of
signal using R4. NTSC signal asks for 4:59 microsecond HSYNC signal and PAL asks for 4.60 microsecond HSYNC signal. Asking 4.59 microseconds NTSC and PAL signals HSYNC ask for 4.60 microsecond HSYNC signal.
Many of the TV experience problems in receiving signals with the correct color for oscilloscope measurements such as, video vectorscope or frequency counter has a different measurement capabilities. If you do not have the necessary equipment measusing, you just adjust R4 so that you get good color workign with your TV.
Final setting is to improve the color subcarrier frequency. NTSC Subcarrier frequency C6 and C7 adjust PAL subcarrier frequency adjustment. You have to adjust them so that you get the best color reproduction