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DLPLCR9000EVM: Pattern rates

Carl H
Prodigy 110 points

Part Number: DLPLCR9000EVM

I am a bit confused concerning the pattern rates. The programmers guide describes how a frame in video mode is displayed.

The minimal exposure time of single patterns is 105us and the bit depth for a single color is 8 so there are 255 intensity levels. How can this work with 60 fps? Having a bit depth of three and comparing a pixel with an intensity level of 255 with one of intensity level 1 means that the time interval of the 255 pixel has to be 255 times as large as the time interval of the 1 pixel. When I say that the short time interval is 105us than the long one would be 255*105 us =  26775 us which is 26.8 ms while 1/60s (60fps) gives 16ms. Where is my mistake?

  • 0
    TI__Expert 3020 points

    Hi Carl,

    We will check and get back to you.

    Thanks,
    Shivakumar

  • 0 in reply to SHIVAKUMAR R
    TI__Mastermind 43165 points

    Carl,

    While this seems confusing the answer turns to be simpler than expected.  The shorter bit times are achieved by Solid State illumination modulation for multi-bit sequences.

    In other words, the shortest load and flip mirrors time is 105 us, but the illumination is not on the entire time.  This does add some dark time for the smaller bits.  For LSB through LSB+2 this is not very significant in the total frame time.

    So lets say for argument sake that I can turn on the illumination for 15.87 us for the LSB and then 2x15.87=31.7 us for LSB+1 and 4X15.86=63.48 us for LSB+2, and LSB+3 will be longer than the 105 us.  The load time for each bit is 105 us with the remaining time as dark time for the LSB through LSB+2.  For the bits above this there is no dark time since there is enough time to load LSB+n during the display of the previous bit.  This makes it possible to display all 8 bits in the 4046 us that the GUI shows if you choose an 8-bit pattern in Pattern On-the-Fly mode.

    For 1-bit depth patterns, there is no sequence so it is 105 us.  If you choose bit depth 8, there is an embedded sequence that takes over and controls the illumination via LED_ENABLES.

    So notice that if you set the bit depth to 8, the minimum exposure time is 4046 us (4.046 ms) which is about 246 8-bit patterns per second.

    Fizix

  • 0 in reply to Fizix
    Prodigy 110 points

    Ah, ok. Nice, I did not concern the opportunity to exploit this "degree of freedom", makes sense.

    Thank you, I got it.