ViewSonic PJ870 Service Manual - Page 66

PJ870 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 tp 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. ViewSonic Corporation [7-6] : Confidential - Do Not Copy