array and 16.3% on the DMD array border and window aperture. The conversion constant is calculated to be

0.00293 W/lm.

The following is a sample calculation for a typical projection application:

• SL = 20 lm

• TCeramic = 55°C

• QArray = QELECTRICAL + QILLUMINATION = 0.045 W + (0.00293 W/lm × 20 lm) = 0.1036 W

• TArray = 55°C + (0.1036 W × 8°C/W) = 55.8°C

7.7 Micromirror Landed-On/Landed-Off Duty Cycle

7.7.1 Definition of Micromirror Landed-On/Landed-Off Duty Cycle

The micromirror landed-on/landed-off duty cycle (landed duty cycle) denotes the amount of time (as a

percentage) that an individual micromirror is landed in the On state versus the amount of time the same

micromirror is landed in the Off state.

As an example, a landed duty cycle of 75/25 indicates that the referenced pixel is in the On state 75% of the time

(and in the Off state 25% of the time), whereas 25/75 would indicate that the pixel is in the On state 25% of the

time. Likewise, 50/50 indicates that the pixel is On 50% of the time and Off 50% of the time.

Note that when assessing landed duty cycle, the time spent switching from one state (ON or OFF) to the other

state (OFF or ON) is considered negligible and is thus ignored.

Since a micromirror can only be landed in one state or the other (On or Off), the two numbers (percentages)

always add to 100.

7.7.2 Landed Duty Cycle and Useful Life of the DMD

Knowing the long-term average landed duty cycle (of the end product or application) is important because

subjecting all (or a portion) of the DMD’s micromirror array (also called the active array) to an asymmetric landed

duty cycle for a prolonged period of time can reduce the DMD’s usable life.

Note that it is the symmetry/asymmetry of the landed duty cycle that is of relevance. The symmetry of the

landed duty cycle is determined by how close the two numbers (percentages) are to being equal. For example,

a landed duty cycle of 50/50 is perfectly symmetrical whereas a landed duty cycle of 100/0 or 0/100 is perfectly

asymmetrical.

7.7.3 Landed Duty Cycle and Operational DMD Temperature

Operational DMD Temperature and Landed Duty Cycle interact to affect the DMD’s usable life, and this

interaction can be exploited to reduce the impact that an asymmetrical Landed Duty Cycle has on the DMD’s

usable life. This is quantified in the de-rating curve shown in Figure 6-1. The importance of this curve is that:

• All points along this curve represent the same usable life.

• All points above this curve represent lower usable life (and the further away from the curve, the lower the

usable life).

• All points below this curve represent higher usable life (and the further away from the curve, the higher the

usable life).

In practice, this curve specifies the Maximum Operating DMD Temperature that the DMD should be operated at

for a given long-term average Landed Duty Cycle.

7.7.4 Estimating the Long-Term Average Landed Duty Cycle of a Product or Application

During a given period of time, the Landed Duty Cycle of a given pixel follows from the image content being

displayed by that pixel.

For example, in the simplest case, when displaying pure-white on a given pixel for a given time period, that pixel

will experience a 100/0 Landed Duty Cycle during that time period. Likewise, when displaying pure-black, the

pixel will experience a 0/100 Landed Duty Cycle.

Between the two extremes (ignoring for the moment color and any image processing that may be applied to an

incoming image), the Landed Duty Cycle tracks one-to-one with the gray scale value, as shown in Table 7-1.

DLP2000

DLPS140B – MARCH 2019 – REVISED MAY 2022

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