DLPA060B July   2015  – November 2024 DLP7000UV , DLP9000XUV , DLP9500UV

 

  1.   1
  2.   System Design Considerations Using TI DLP® Technology in UVA
  3.   Trademarks
  4. 1Introduction
  5. 2Thermal
  6. 3Duty Cycle
  7. 4Optical
  8. 5High Demagnification Systems
    1. 5.1 Incoherent Sources (Lamps and LEDs)
    2. 5.2 Coherent Sources (Lasers)
  9. 6Conclusion
  10. 7References
  11. 8Revision History

3 Duty Cycle

Within all applications, the DMD benefits from operating at an average 50% landed-on/off duty cycle, but this consideration becomes even more relevant when operating under UVA wavelengths. The landed-on/landed-off duty cycle indicates the percentage of time that an individual micromirror is landed in the on-state versus the off-state. The switching time taken to switch between states is considered negligible and is ignored when determining this duty cycle.

This duty cycle is expressed as the landed-on percentage divided by the landed-off percentage. For example, a pixel that is landed-on 75% of the time and landed-off 25% of the time is denoted as 75/25 duty cycle. Note that the two numbers that express duty cycle always sum to 100.

Operating at or near 50/50 duty cycle promotes the longest DMD performance. There are two possible scenarios of operation under this consideration:

  1. The first scenario is when the duty cycle histories of the DMD pixels are not tracked and subsequently are not known. In this situation, operating the DMD at 50/50 whenever the DMD is not actively illuminated(1) drives all pixel duty cycle historical averages back toward 50/50 duty cycle. The longer the DMD is operated at 50/50 in any and all available system quiescent periods, the closer the overall historical average approaches 50/50 duty cycle.
    CAUTION:

    (1) DMD illumination subsystems (Lamps, LED, Lasers) must be disabled or shuttered at any time that DMD patterns are not needed or are not being projected to the fabrication surface. Do not use the DMD as the primary illumination shutter.

  2. The second scenario is when the history of each individual pixel is tracked over time. In this case, applying the reverse duty cycle to each pixel for an equal period of time (when not actively being used for patterning) causes the historical average for each pixel to approach 50/50 accumulated duty cycle. For example, if a pixel is driven at 62/38 duty cycle during operation, then driving the pixel at 38/62 duty cycle for an equivalent time during quiescent periods causes the pixel average duty cycle to approach 50/50. Note that this is also possible to drive at a higher reverse duty cycle for a shorter period of time so that the overall average is 50/50.