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Original question:

DLP Link: What's in the white flash signal that's determining which side to see (left/right)?

DLP Link Protocol

Yamini Patel
Prodigy 200 points

Hi,

We are using DLP Projectors in our product and we want to know about how DLP links works and what is white flash light signal?

We got some basic knowledge about it and referred some link from TI Forum and Ti patent (US8237779B2) but still we want to know more about it.

So can you please tell us the process for the NDA ?

Thanks,

Yamini

  • 0
    TI__Intellectual 2290 points

    The DLP Link(TM) pulses will generally be Red, Green, or Blue (not white); this is determined when implementing the design (by the manufacturer/oem/design house, etc.).

    What is it that you are looking for?  What is the purpose?  Are you looking to build a projector, or DLP Link capable glasses, or...?

  • 0 in reply to Gary S
    Prodigy 200 points

    Hi Gary,

    We are making DLP based 3D Glasses and therefore we need the details. If it is okay, can we move this discussion in email so we can respond quickly to each other?Kindly drop an email or share your email id so we can communicate over email.

    Thanks,

    Yamini

  • 0 in reply to Yamini Patel
    TI__Intellectual 1930 points

    Hi Yamini,

    In addition to Gary's response, I am checking to see what information is proprietary if we actually need an NDA in light of the already publicly released patent.

    Jason

  • 0 in reply to Yamini Patel
    TI__Intellectual 1930 points

    Hi Yamini,

    We have determined that this information no longer requires and NDA.  Please see the attached document that describes the behavior and timing of the DLP Link.  Let us know if this addresses your questions.

    Thanks,

    Jason

    dlp_link_3d_glasses_nonNDA.pdf

  • 0 in reply to Jason Thompson
    Prodigy 200 points

    Hi Jason,

    We have referred the PDF file you sent but we have some few questions mentioned below.

    1. What are OEM, SW, and CW?
    2. What does this line mean "The period between odd or even pairs of pulses is equal to the frame period since that is the sum of a long and a short inter-pulse period." In accordance with this diagram:
    Thanks,
    Yamini
  • 0 in reply to Yamini Patel
    TI__Intellectual 1930 points

    Hi Yamini,

    Gary is going to provide a more detailed answer soon.

    Thanks,
    Jason

  • +1 in reply to Yamini Patel
    TI__Intellectual 2290 points

    Hello Yamini,

    > What are OEM, SW, and CW?

    OEM is the Original Equipment Manufacturer - The designer/builder of the projector.  CW is Color Wheel; this particular document refers to color wheels, but it works the same for other illumination sources as well.  SW is software; the software running in the controller is involved in trying to make sure things are in sync; in some cases it may actually all be in hardware.

    > What does this line mean "The period between odd or even pairs of pulses is equal to the frame period since that is the sum of a long and a short inter-pulse period." In accordance with this diagram.

    If you measure the time between every other pulse, the time should be the video frame time:

    In newer controllers it is technically possible for the projector manufacture/designer use frame rate conversion to display lower input frame rates at higher display rates.  3D display rates can be 144Hz or possibly higher.  Generally, a 24Hz input (48Hz per eye input) would be displayed at 3x = 144Hz.  Flash rates of 48Hz, 60Hz, 96Hz, 120Hz, 144Hz, 180Hz, 192Hz, and 240Hz (and others) are all theoretically possible depending on the projector implementation.  The lower rates, like 48Hz, 60Hz, and 96Hz are generally avoided.

    For the best compatibility, one probably needs to support at least 144Hz and lower flash rates.


    Regarding Dark Time:

    "E" in the diagram you posted is the "dark time".  During this time, the image is dark.  This gives the 3D glasses/system time to switch, minimizing left-eye/right-eye crosstalk.  The glasses need to be able to switch in this time to minimize crosstalk.  The dark time value is determined by the projector brand/OEM/designer based on the 3D solution(s) they plan to support; it may vary from brand to brand and model to model. 

    The dark time value is selected at design/build time.  A product could have support for multiple dark time options. I have seen product specs/manuals online supporting 0.65ms, 1.3ms, 1.95ms, and 2.5ms; while others do not list a time at all.

    A good target would be less than 1000us switching time to ensure good compatibility with many projectors.  

     

    A few other notes:

    The OEM can also invert the left and right eye signal internally; some expose this in their projector interface, some may not. It is a good idea to be able to invert this in the glasses if needed.

     

    The choice of what to implement is up to the projector designer/manufacturer, their product requirements, and system capabilities/design/choices.  Every product could be different.  

     

    I hope that helps.

     

    Regards,
    Gary