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DLP4500-C350REF: Timing artifacts

Song Liu
Prodigy 130 points
Part Number: DLP4500-C350REF

Dear TI professionals:

I am using DLP4500-C350REF to generate rectangular wave forms. I do this by using the pattern sequenc mode and feed in a 24bit 60hz video file that alternate between on/off states. Since there are 24 RGB bits in each frame, i can alternate between on/off, and generate a wave form of period 2/1440=1.38 milliseconds. The following the captured light intensity wave form:

But when i try to generate other frequencies, for example a rectangular wave with period of 239/1440 seconds, i observe that there is an artifact after each rising and falling edge. I have circled out the artificact in the captured light intensity waveform as follows. Besides the artifact, the frequency of the waveform is correct. Could you please tell me where does this artifact come from? Thanks

  • 0
    TI__Mastermind 30600 points
    Hi Song,

    Thanks for your question and welcome to the DLP Forums! This is an interesting application of our EVM - what are you using these square waves for?

    You're in pattern sequence mode, so all bits should have equal weight and have the exposure that you set for them. Can you tell me what your pattern settings are for the cases you described above?

    How did you create 239/1440?

    -Paul
  • 0 in reply to Paul Goedeke
    Prodigy 130 points

    Hi Paul:

    I am using this as an light communication application. My settings for the pattern sequence mode are as follows:

    Exposure time: 1/(24*60)=694 us. Exposure period: 694us.

    Trigger: VSync Video

    Color: white

    And I have added all 24 frames: R0, R1, R3...R7, G0, G1..G7,B0,B1..B7; and I have unchecked "insert black between frames"

    The idea underlying my application is very simple. In order to generate a square wave with a period of 2/1440 seconds, I simply display a static image with the following 24 color bits:

    0 1  0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1

    In order to generate a square with a period of 3/1440 seconds, I use the following still image:

    011011011011011011011011

    In order to generate a square with a period of 4/1440, I use:

    001100110011001100110011

    Of course, I need to ensure that the light intensity from the Red green and blue LEDs are the same. I am currently using default LED currents, and light intensity waveform captured shows that they are roughly on the same light intensity level.

    Any ideas on how to get rid of the artifact? I heard that temporary artifact can be prevented by fixing the buffer swap but I am not sure.

    Thanks LS

  • 0 in reply to Song Liu
    TI__Mastermind 30600 points

    Thanks for describing how you create the patterns, it is enlightening. Does the artifact only occur at certain periods? Or above a threshold? It looks like from your first image that you're not seeing the artifact but in the longer period image you are. I'm wondering if it only occurs in with odd periods (3/1440, 5/1440, etc.) or above a certain length period.

    - Paul

  • 0 in reply to Paul Goedeke
    Prodigy 130 points

    Hi Paul, sorry for the late reply. i have solved the problem. It is because my video coding is incorrect. Thanks