• State Resolved
  • Locked Locked
  • Replies 5 replies
  • Subscribers 48 subscribers
  • Views 939 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

THS8135 (with OMAP3530)

Josh Watts
Intellectual 945 points

Other Parts Discussed in Thread: OMAP3530, THS8135

I've managed to get the right timings for our setup of the THS8135 and OMAP3530 (including the 8 pixel shift for the delay in the THS8135), but I am still having trouble getting a clean image. Solid fill colors appear correct, and a simple color-bar test pattern shows multiple colors correctly, but complex color changes like gradients are generally overly bright and in some spots show incorrect colors (red pixels in the middle of a black to white gradient). I think this may be due to not using the /BLANK input on the THS8135.

Should we have connected /BLANK to the OMAP3530's (inverted) H-SYNC signal? Or is there something else I should be looking for? (H-SYNC and V-SYNC are currently "directly" connected to the VGA connector through a level converter)

  • 0
    TI__Genius 16810 points

    Josh,

    AC_Bias is the OMAP signal that is typically used as a DE/blank singal with the THS8135.  The blanking signal needs to include the entire blanking interval, not just the HSYNC interval.

    You may want to check the DAC outputs to see if they are within a 0-700mV range. 

    For generic RGB outputs, tie M1 and M2 to logic low level, and /Sync and Sync-T to logic high level.

  • 0 in reply to Larry Taylor
    Intellectual 945 points

    Thank you for the prompt reply! :-)

    I've got the acbias signal enabled and it's operating when it should, but I think my re-work broke something else near-by... I'm getting ~980mV on the green output and ~500mV on the red and blue outputs. I know it's outside of the scope of my original question, but any thoughts on what might cause this condition? I tried using the OMAP's pull-up and pull-down resistors to hold ac-bias at high and low, and I've returned to using the same 10k ohm resistor to 1.8V I was using before, no good. :-(

  • 0 in reply to Josh Watts
    TI__Genius 16810 points

    Josh,

    The THS8135 has current output DACs.  The output voltage level depends on the output load resistor and RGB termination.  The full-scale adjust resistor sets the full-scale output current of the DACs equally, so this appears to be related to individual DAC load resistors.  When viewing on a scope and not connected to a typical video load, make sure the scope input impedance is set the same for all channels.  It is best to check the outputs with the proper video load.

    I would also check the M1, M2, /Sync, and Sync-T levels to make sure they are set up for generic RGB with no sync insertion.

    M1=M2=0V

    /Sync = Sync-T = 1.8V

    /Blank = 1.8V if not used

  • 0 in reply to Larry Taylor
    Prodigy 240 points

    Hi Josh,

    Did the issue get resolved for you?

    We are also facing the exact same issue.

    regards,

    Imtiyaj

  • 0 in reply to imtiyaj
    Intellectual 945 points

    Imtiyaj: Connecting AC_BIAS to the DE/BLANK pin on the THS8135 is critical for proper VGA display. The OMAP3530's display does not reset the pixel pins to 0 during HSYNC, so you must use the DE/BLANK pin on the THS8135 to override the input data pins and produce a proper blank level which the VGA monitor needs to calibrate the voltage for "black". IIRC (this was several months ago) we were able to use the AC_BIAS output for this. I hope that answers your question, if not then I recommend opening a new topic (if you haven't already)