I need to convert an RGB signal to S-video and composite. Apparently the Analog Devices AD-725
There's a schematic in that datasheet which I've extracted as an image file here:
but as a novice there are a few things I don't quite understand:
1) there are pins for digital and analog power supplies. Do I really need two different power supplies for this, or can I simply connect pin 4 (analog +5V) and pin 14 (digital +5V) together to a +5V supply, then pin 2 (analog GND) and pin 13 (digital GND) together to GND of the power supply?2) I don't quite understand the oscillator on pin 4. I need a PAL signal, but I'm confused about the "OSC" as it looks like a simplified symbol rather than a component. Do I simply get hold of a 17.734475 MHz oscillator as in one of those metallic square thingies with 4 pins, or is the schematic referring to a more complex circuit you have to figure out yourself?
3) Regarding the luma-trap which is supposedly going to improve the signal, at the end of the circuitry connected to pin 1 (encoding standard) and pin 12 (luminance trap filter) it says "NTSC/PAL" at the end. Where do I connect this?4) I can't see any reason for power down the circuitry in my application, thus pin 5 (chip enable) isn't needed. However, the datasheet says that a logic high (TTL) enables the encoding function while a logic low powers down the chip when not in use. Should I just connect this to the +5V line from the power supply? On second thought, I see that it says "..powers down the chip *when not in use*". Is there some sort of detection circuitry which senses when a TV etc. is connected to the S-video or composite outputs?
5) my application will "tap" the RGB and sync signals several places. In other words, in addition to the S-video/composite circuitry the AD725 will provide I will also be able to connect an RGB monitor, TV and (S)VGA monitor to it. I suppose I just can't simply tap into the RGB output of the computer for all these devices, but need to buffer or recondition the signals first, right? I believe this is what the AD-8073a) can I use several AD8073 circuits (copying the same connection as shown in the schematic) connected to the RGB source, then use those different outputs for all the various display devices mentioned above, or do I need a different circuit for this?
b) next to the RGB monitor in the schematic it says "from VGA port" referring to the VSYNC and HSYNC signals. Is this simply the output of the "VGA connector" on the left in the schematic, or is it via some buffering circuitry etc?
c) does it make any difference if I connect the AD725 to the outputs of the AD8073, and the RGB monitor directly to VGA connector, or do I need to follow the schematic and connect the AD8073 directly to the VGA connector and have the RGB monitor go to the outputs of the AD8073? I guess this question relates a lot to questions 5 and 5a.
Thanks :-)