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DLPC1438: Exposure frames, dark frames and exposure time control

David Stephanson
Prodigy 20 points
Part Number: DLPC1438
Other Parts Discussed in Thread: DLPA2005, , DLP300S

Hello,

I'm trying to make sense of the DLPC1438 way of controlling the light which uses dark frames and exposure frames and in general of the DLPC1438 + DLP300S + DLPA2005 combination.

The DLPC1438 has a maximum pattern rate of 60Hz both for binary and 8-bit patterns. Looking at the DLPC3479 documentation for reference, frames could be cut into multiple patterns as one frame is constituted of 24-bits. For example, one 24-bit frame could be cut into 3x 8-bit patterns.

In the case of the DLPC1438 as the patterns have a maximum rate of 60Hz, is it correct to assume that the minimum exposure time is 1/60 sec or 16.6 msec ? Or is one frame (1/60 sec) divided into exposure and dark frames (for example: Number of exposure frames = 1, Number of dark frames = 2 -> 33% of 1/60 sec ON and 66% of 1/60 sec OFF per 1/60 sec)? 

Thank you for our help,

David

  • 0
    TI__Genius 9945 points

    Hello David,

    For DLPC1438, the maximum support pattern rate is 60Hz for Test pattern Generator mode and External Print Mode. Each VSNYC signal edge matches the start of a new frame (either a dark frame or a exposure frame), so there should be light for a full 16.667ms frame. Also, the dark frames always go first. 

    I hope this helps.

    Regards,

    Lori 

  • 0 in reply to Lori Wang
    Prodigy 20 points

    Hello Lori,

    Thank you for your help.

    I don't quite understand the use of dark frames in this case. Is it to have enough time for the pattern to be showed on the DMD ? If so, is a minimum number of dark frames required in order for the DMD to be ready to output the full exposure frame ?

    Best regards,
    David

  • 0 in reply to David Stephanson
    TI__Genius 9945 points

    Hello David,

    Please see the explanation in the DLPC1438 Software programmer's guide below. It's recommended to allow 3 or more dark frames before exposed frames, but you should be able to test the needed number of dark frames in your system.

    Regards,

    Lori 

  • 0 in reply to Lori Wang
    Prodigy 20 points

    Hello Lori,

    Okay digging more deeply in the documentation, even if using the FPGA buffers, the dark frames are required which I don't understand why because the role of the buffers is to be able to project and to upload a pattern at the same time. Does this mean that it can provide 60 frames per second but then only 1 new pattern every 4 patterns making it 15 different patterns per second ?

    I understand that this might be limited by the use of the XPR to increase the resolution. What if we would keep the native DMD resolution (1280x720) ? The required bandwidth is reduce by a factor of 4 and we could perhaps reach the 60 different patterns per second ?

    Best regards,

    David

  • 0 in reply to David Stephanson
    TI__Genius 9945 points

    Hi David,

    For clarify, the sequence used on the DLPC1438 support 60Hz host VSYNC rate which means a 60Hz subframe rate (15Hz frame rate) when you use 4-way XPR option. If you use the native resolution 1280x720 and without an actuated XPR, then the frame rate is 15Hz.

    Regards,

    Lori