Plasma Display Panels are like CRTs in that they are emissive and use phosphor, and like LCDs in their use of an X and Y grid of electrodes separated by an MgO dielectric layer and surrounded by a mixture of inert gases - such as argon, neon or xenon - to address individual picture elements.
They work on the principle that passing a high voltage through a low-pressure gas generates light. Essentially, a PDP can be viewed as a matrix of tiny fluorescent tubes which are controlled in a sophisticated fashion. Each pixel, or cell, comprises a small capacitor with three electrodes. An electrical discharge across the electrodes causes the rare gases sealed in the cell to be converted to plasma form as it ionises. Plasma is an electrically neutral, highly ionised substance consisting of electrons, positive ions, and neutral particles. Being electrically neutral, it contains equal quantities of electrons and ions and is, by definition, a good conductor. Once energised, the cells of plasma release ultraviolet (UV) light which then strikes and excites red, green and blue phosphors along the face of each pixel, causing them to glow.
Within each cell, there are actually three subcells, one containing a red phosphor, another a blue phosphor, and the third a green phosphor. To generate colour shades, the perceived intensity of each RGB colour must be controlled independently. While this is done in CRTs by modulating the electron beam current, and therefore also the emitted light intensities, PDPs accomplish shading by pulse code modulation (PCM). Dividing one field into eight sub-fields, with each pulseweighted according to the bits in an 8-bit word, makes it possible to adjust the widths of the addressing pulses in 256 steps. Since the eye is much slower than the PCM , it will integrate the intensity over time. Modulating the pulse widths in this way translates into 256 different intensities of each colour - giving a total number of colour combinations of 256x256x256 = 16,777,216.
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