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_PI875 Service Manual |
Note 10 : Window Aperture
A shield is utilized on the interior perimeter of the window to improve system contrast and
reduce the thermal loading caused from the overfill of incident light. The shield may be of either
reflective or absorptive type. Incident light of up to f/2.8 (input cone angle of 20°+ 10°) shall be
supported without interference (active area shading) from the window aperture. The window aperture
is designed to accept light at an incidence angle of < 52° within the perimeter of the window. Light
that falls outside the window clear aperture or outside the specified angle will have detrimental effect
on system optical and thermal performance. The window aperture is depicted in Figure 7, Figure 9,
and Figure 10. The packaged assembly shall accommodate incident light from the direction shown in
Figure 9 and Figure 10. Section Z-Z in Figure 10 illustrates the angles and direction of the projected
and dump light with incident light from the indicated direction. The edges of the package reflective
shield aperture near the DMD active area shall not cause scattering of the incident or dump light to be
objectionable in the projected image area. Specular reflectivity is defined for the illumination
conditions in Table 2.
Note 11 ; Thermal Performance
The DMD is designed to conduct residual heat energy to the back of the package where it can be
removed by an appropriate heat sink. A device configured for a particular application can be
manufactures with a thermal stud designated for that appication (see Appendix A-). The thermal stud
mounting location is shown in Figure 8. The heat sink and cooling system must be capable of
maintaining the package within the specified operational temperatures. The total heat load is largely
driven by the incident light absorbed by the active area although other significant contributions that
should be considered include light energy absorbed by the window aperture and electrical input
power. The portion of incident light absorbed by the active area is determined from the active area
absorption coefficient in Table 1. The absorption by the window aperture is the light neither
specularly nor diffusely reflected according to the window aperture reflectvity parameters shown in
Table 1. Optical systems should be designed so that no significant light energy falls outside the
window clear aperture as shown in Figure 9, as any significant additional thermal load on the case top
can damage the device.
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