• State TI Thinks Resolved
  • Locked Locked
  • Replies 3 replies
  • Answers 1 answer
  • Subscribers 29 subscribers
  • Views 381 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

DLP7000: flickering issue during pattern switching

Yufei Wang
Prodigy 10 points
Part Number: DLP7000

Dear technical team,

We are using a DLP7000 by projecting it with a collimated laser beam (7mm of diameter). In our application, we are switching multiple ‘On' state patterns(1-bit binary patterns in one sequence) at different position within the illuminated area on DMD. The dimension of our patterns is smaller than our beam size. And we are measuring the optical power of the first order diffraction using a bucket detector. 
We noticed that the global switching rate of our controller board is 22272 Hz, which means a 45 μs time duration. According to 8.7.1 of DLP7000 technical document, this switching time is negligible.  However, at the collection end, we detected a very strong signal peak within this 45 μs. It turned out that when the DMD is switching patterns, all the micro mirrors will be reset to 'On' states instead of a flat or 'off' state. Thus, we are receiving signals from the whole illuminated area, much higher than what we will get from our patterns. This flickering issue will saturate or even damage our detector.
We would be grateful if you could kindly give any solutions to overcome this flickering issue. Is it possible to leave the micromirror in 'off' or flat states during pattern switching? 
  • 0
    TI__Guru 54500 points

    Hello Yufei,

    What is the orientation of the incident light relative to the normal of the DMD?

    What is the wavelength of light you are using?

    What is meant by the "first order"?  

    Please be aware that there are only two operational states for a DMD - "on" or "off".  Parked ("flat) is not an operational state..  During operation, the mirrors may briefly pass through flat, but do not remain there.  

    Fizix

  • 0 in reply to Fizix
    Prodigy 10 points

    Hi Fizix,

    Many thanks for your prompt reply. We are using a 532nm laser. The angle of incident light relative to the normal of the DMD is 12 degree.

    Sorry for the confusion, we are capturing the first diffraction order of the reflected pattern.

    I have attached a schematic figure for better understanding on the issue. It seems that when DMD switching the patterns, all micromirrors will be reset to 'On' state. It will cause a power boost to our detector.

    regards,

    Yufei

  • 0 in reply to Yufei Wang
    TI__Guru 54500 points

    Hello Yufei,

    First, your diagram is very good and very helpful.

    Please see Using Lasers with DLP® DMD technology  By my calculations, you are operating somewhere near the 4,4 order.

    I would suggest trying the incident light at about 22.5 degrees from the normal.  This will operate near the 7,7 order normal to the DMD.  This order should be much brighter, and the "anomaly" will be much lower relative to the signal.

    To determine which order your detector is at, turn the DMD off and find the brightest order in the output field.  This is the 0,0 order.  Count along the diagonal of the diffraction pattern (refer to the linked application note above).  This will be along the n=m line of the orders - i.e. (n,n).

    I believe what is happening is that at the order you are working in, the pixels that are transitioning from "on" to "off" briefly pass through a blaze condition. The momentary blaze condition is MUCH more efficient than the order you are using so that you get a spike in the signal.

    Converting to the illumination scheme I suggested, should correct what you are experiencing.

    Fizix