7.5.1.3 Illumination Overfill

The active area of the device is surrounded by an aperture on the inside DMD window surface that masks

structures of the DMD chip assembly from normal view, and is sized to anticipate several optical operating

conditions. Overfill light illuminating the area outside the active array can create artifacts from the mechanical

features surrounding the active array and other surface anomalies that may be visible on the screen. The

illumination optical system should be designed to limit light flux incident anywhere outside more than 20 pixels

from the edge of the active array on all sides. Depending on the particular system’s optical architecture and

assembly tolerances, this amount of overfill light on the outside of the active array may still cause artifacts to still

be visible.

7.6 Micromirror Array Temperature Calculation

0.60

7.06

TP1 (ceramic)

Window Edge

(4 surfaces)

Figure 7-1. DMD Thermal Test Point

The micromirror array temperature can be computed analytically from measurement points on the outside of

the package, the package thermal resistance, the electrical power dissipation, and the illumination heat load.

The relationship between array temperature and the reference ceramic temperature is provided by the following

equations:

TARRAY = TCERAMIC + (QARRAY × RARRAY–TO–CERAMIC)

(1)

QARRAY = QELECTRICAL + QILLUMINATION

(2)

QILLUMINATION = (CL2W × SL)

(3)

• TARRAY = Computed DMD array temperature (°C)

• TCERAMIC = Measured ceramic temperature (°C), TP1 location in Figure 7-1

• RARRAY–TO–CERAMIC = DMD package thermal resistance from array to outside ceramic (°C/W), specified in

Section 6.5

• QARRAY = Total DMD power; electrical plus absorbed (calculated) (W)

• QELECTRICAL = Nominal DMD electrical power dissipation (W)

• CL2W = Conversion constant for screen lumens to absorbed optical power on the DMD (W/lm)

• SL = Measured ANSI screen lumens (lm)

The electrical power dissipation of the DMD is variable and depends on the voltages, data rates, and operating

frequencies. A nominal electrical power dissipation to use when calculating array temperature is 0.045 watts.

The absorbed power from the illumination source is variable and depends on the operating state of the mirrors

and the intensity of the light source. The equations shown previously are valid for a 1-Chip DMD system with a

total projection efficiency from DMD to screen of 87%.

The conversion constant CL2W is based on DMD micromirror array characteristics. It assumes a spectral

efficiency of 300 lumens/watt for the projected light, and an illumination distribution of 83.7% on the DMD active

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DLP2000

DLPS140B – MARCH 2019 – REVISED MAY 2022

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