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HDMI to LVDS Conversion Options

Bernie Thompson TI
Mastermind 41665 points
Other Parts Discussed in Thread: SN75LVDS83B, TFP403, TFP401A, TFP401, THS8135, TVP7002, TFP410, DS90C387A, TFP501, DS90C387

I was wondering if TI has anything to offer for a HDMI to LVDS solution? I must admit I am not very familiar with the high speed interface lineup, but looking through the parts I did not see anything that would perform this particular function directly, though it looks like it may be possible with unencrypted video with a pair of devices (i.e. DVI receiver coupled to a LVDS transmitter).

In any case I was wondering what the best solution TI has to offer for this would be if there is anything practical, and if this is the proper place to ask, thank you for your help.

  • 0 in reply to Elias Villegas M.
    Prodigy 20 points

    Hi Elias,

    Thanks for your suggestions.

    I wanted to try out what you suggested but unfortunately, I wasn't able to find a  PC with HDMI input (they all come with HDMI output only). So here's what I did instead:

    1. Connect Android phone to a HDTV with speakers using MHL-to-HDMI converter.

    Results: sound is audible from the speakers. This confirms the existence of audio signals in the TMDS.

    2. To check if the audio component in TMDS does mess up with the detection of blanking signals, I probed the HSYNC and VSYNC signals on the TFP401A.

    Results: VSYNC looks good (cross-checked against a known-working setup that gets HDMI output from PC instead of Android phone). HSYNC looks abnormal and irregular - lots of missing blanking periods it seems.
     

    3. In order to remove the audio components in the TMDS, I used an MHL-to-DVI adapter (from monoprice.com) instead of the MHL-to-HDMI converter. According to the website, the MHL-to-DVI  adapter does not support audio.

    4. With the MHL-to-DVI connected, I probed the VSYNC and HSYNC signals again. This time, both signals show regular blanking periods - no missing pulse. However, the HSYNC is inverted (i.e. active low), which is the only noticeable difference compared with the the working setup.

    All in all, the lcd panel is still not displaying any image and I'm thinking the inverted HSYNC signal might be a contributing factor. Any advice/suggestions?
     Thank you.

  • 0 in reply to Woon Tiong Ang
    TI__Mastermind 36085 points

    Hello Woon,

        Yes you are correct, is highly possible that the inverted HSYNC signal is causing the issue, maybe is an adapter  malfunction, could you verify the behavior with an adapter from a different brand?

    Best regards,

    Diego.

  • 0 in reply to Woon Tiong Ang
    TI__Guru* 76130 points

    Hello,

    The TFP410 can be configured to accept an HSYNC active-low or active-high.

    You must configure this by i2c writing to the HS_POL bit (bit 4 in the sub-address 33h). 

    Regards.