But until recently, this possibility seemed as remote as developing a digital loudspeaker to interface with digital audio. Invented in 1987 at Texas Instruments, the DMD is a fast, reflective digital light switch. It can be combined with image processing, memory, a light source, and optics to form a DLP system capable of projecting large, bright, seamless, high-contrast color images with better color fidelity and consistency than current displays. Each light switch has an aluminum mirror that can reflect light in one of two directions depending on the state of the underlying memory cell. By combining the DMD with a suitable light source and projection optics, the mirror reflects incident light either into or out of the pupil of the projection lens.
Gray scale is achieved by binary pulsewidth modulation of the incident light.
Color is achieved by using color filters, either stationary or rotating, in combination with one, two, or three DMD chips. The DMD light switch is a MEMS structure consisting of a mirror that is rigidly connected to an underlying yoke. The yoke in turn is connected by two thin, mechanically compliant torsion hinges to support posts that are attached to the underlying substrate. Electrostatic fields developed between the underlying memory cell and the yoke and mirror cause rotation in the positive or negative rotation direction. The fabrication of the DMD superstructure begins with a completed CMOS memory circuit.