Purely for hobby, I am working on an RGBHV (VGA) to YPbPr (Component) converter circuit for old games consoles modified to output RGBHV on a VGA cable. From the game consoles, the RGB signal is taken from before the composite encoder chip and the HV sync signals are generated by a TI LM1881 chip being fed with composite video from after the composite encoder chip. This creates valid 15khz VGA that works with my VGA capture card for high quality video capture.
Now, the converter I am working on needs to take this VGA signal and convert it to YPbPr to display on a CRT TV. In my inexperienced attempt at scrapping this circuit together, I have used two LT6550 chips and Linear's application note. Here is the circuit: Exported circuit with annotations (Import & Simulate in http://www.falstad.com/circuit/). I have also attached a picture. The top part (RGB->YPbPr) is pretty much verbatim from the application note, the only thing I have added was the bottom part for adding the sync information to Y.
My two questions are:
What are the waveforms supposed to look like for YPbPr? I can find heaps of information on google about composite video, VGA, and some about the Y component and understand what those waveforms are supposed to look like on-the-wire in an actual application, but PbPr information seems scarce as far as actual oscilloscope style displays go, even though I know Pb is 0.565(B-Y) and Pr is 0.713(R-Y). In a month or two I will be able to look at the waveform with an osc. myself.
Are there any glaring problems with the circuit? Not knowing what the waveform is like, I find it odd that Y is -300mV sync 0mV to 700mV signaling but Pr and Pb are -350mV to 350mV signaling. Does this mean I need to AC couple Pr and Pb? Or do I need to level shift Pr and Pb up by 350mV? Or are these voltages valid? I prefer DC coupling wherever possible, I have had crappy black levels with AC coupling in the past somewhat mitigated by larger capacitors
.
