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RGsB to YPbPr

Lorenzo Lutti
Intellectual 665 points

Other Parts Discussed in Thread: OPA698, THS7373, THS8200, TVP7002

I need to convert an high-definition RGsB signal (up to 1080p and UXGA) to a YPbPr signal. If the input signals are DC-coupled (i.e. the black level is fixed to 0V) the conversion looks quite easy, I can use a limiting amplifier such as the OPA698 as half-wave rectifier to remove the negative syncs, and some high-speed amplifiers to do the color space conversion. But if the input signals are AC coupled, I'm not sure which is the best solution to minimize the signal path loss: I could use a video amplifier with DC restore functions (such as a THS7373) trying to bias the R and B channels so that the output black level is the same of the G channel, then use again the OPA698 to remove the sync tip, then the color space conversion, then maybe another THS7373 to AC couple the output again. But this seems very convoluted, considering that I have to handle high-speed signals.

So my question is: can I safely assume that most of "real world" RGsB signals are DC-coupled? If not, which is the cleanest way to solve this problem?

Thank you!

  • 0
    TI__Genius 13935 points

    I am not sure how to answer this.  Although the video standards are written around a DC referenced signal there are conditions where you signal will come in with a different absolute voltage.  This partly depends on how good your system ground is and how robust the cabling is.  With good cables and a low impedance ground you should be fine, but if the video cables are required to provide the ground there could be issues.

    Also, I think that a lot of video sources are AC coupled because they run on batteries or single ended power supplies and cannot swing sync tips below ground. 

    Have you looked at the TVP7002 or the THS8200?

    http://e2e.ti.com/support/data_converters/videoconverters/f/376/p/52878/731188.aspx