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What is the status of DMD mirrors between pattern transition

Jinyang Liang10035
Intellectual 295 points


Hi,

We would like to use DMD to do some time-dependent control. The idea is to generate a bunch of DMD patterns and circle them through.

But we require that there should always be light reflect from DMD - meaning we can't have a dark frame (all pixels "OFF") between adjacent DMD patterns.

 

So, would you please tell me some details about DMD pixel status during pattern switching? Are all mirror turned off between adjacent patterns? 

Why does the DMD act this way? Anything due to API function? How can be get rid of it?

 

I thought this was a problem for previous DMD products but it seems that it has been solved later. Is this true? 

 

Thanks,

Jinyang

  • 0
    TI__Genius 9935 points

    Hello Jinyang,

    I'm not sure that I understand your concern, but let me try to address it with a description of how the DMD array works.

    When the DMD is active, each mirror is in one of two latched positions - either +12 degrees ("on") or -12 degrees ("off"). The "on" and "off" are with respect to the illumination. When the mirrors are "floated", or powered off, the mirrors float to a non-latched condition, but that position is not defined or specified. The float position is not an active position.

    When a pattern is on the DMD, all of the mirrors are latched in one of the active positions, either "on" or "off". When a new pattern is loaded, the mirrors move to their new latched positions. If a mirror which was "on" is now "off", it will move from the "on" position to the "off" position by swinging from one side to the other, and then settling. This takes a few microseconds.

    If a mirror which is "on" is "on" again in the new frame, the mirror will still move slightly, but it will not move all the way from one side to the other. However, it still has to settle into the "on" position. This also takes a few microseconds. The same thing happens for an "off" mirror which will also be "off" in the new frame.

    Even though all of the pixels are activated for each new frame (pattern), there is no "all off" stage between patterns.

    I hope this clarifies things a little.

    Best regards,

    Pascal

     

  • 0 in reply to Pascal DLP
    Intellectual 295 points

    Pascal,

    Yes, you fully understand my question and gave a great answer. 

    Now, it seems that the mirror moves slightly in both cases (from "ON" to "OFF" and stays "ON"). I wonder how big this move is? How does this affect the image quality? Any measurement or specific document about this?

     

    Thanks,

    Jinyang

  • 0 in reply to Jinyang Liang10035
    TI__Genius 9935 points

    Jinyang,

    I'm glad that I answered the right question, then.

    How big is the move for a mirror which is not changing its tilt state over a frame update? It is difficult to answer this quantitatively, but it is correct to say that it is not a big move. That is, it does not swing up in a large arc of rotation, then come back down again. It is a rather short and quick release and re-capture pulse.

    How visible is this? My question is: why is the DMD being illuminated during the pattern transition time? Is the illumination constant - that is, not synchronized with the patterns? In many (e.g. - video) modes, the DMD illumination would be off during the time that the mirrors are moving and settling, and therefore there would be no visible effect.

    Of course, if the illumination is constant during a DMD reset (change of pattern) then it will be possible to see the fluctuation in the reflected light from the mirrors as they move and settle, in both transition cases - same and opposite. Also, the angle of mirror movement and the degree to which this affects the pixel brightness-vs-time profile depends upon the angle of acceptance of the pick-up optics. With fast optics, the transitions tend to be very sharp between bright and dark. With slower optics, more variation in light levels can be seen as a result of mirror tilt variations.

    Best regards,

    Pascal