Plasmatron
Encyclopedia
The Plasmatron, or technically plasma addressed liquid crystal (PALC) is a color television
display technology developed by Tektronix
and Sony
in the 1990s. PALC displays combine rows formed from liquid crystals
with columns formed from plasma cells
, the later replacing the transistorized switching in a conventional LCD. Although PALC was successfully developed, thin-film transistor
based LCD devices improved to offset PALC's advantages, and PALC development has been largely abandoned since the early 2000s.
in the U.S. Through the late 1980s and early 1990s he developed and patented a number of concepts that used plasma
to provide a switching element for a variety of uses. When the project he was working on was canceled, he turned his attention to using the plasma elements as LCD switches, and the PALC system was born.
In 1993 Tektronix licensed the technology to Sony
, and together they started development of the Plasmatron televisions. In October 1996 Sony entered a three-year arrangement with Sharp Electronics to share development, with Sharp's role being to help improve the effective display angles. In July 1997 the group was joined by Philips Electronics to improve the resolution of the devices, reduce power consumption and increase brightness. Sony and Sharp both produced high-definition television
prototypes using the PALC technology, but these never made it to production.
PALC was offset by the rapid introduction of thin-film transistor
s, which allowed individual cells of the LCD to be addressed directly. A grid of rows and columns allows the transistors to be turned on or off just like the plasma cells, but without the need for high voltages or resetting pulse. At first these devices were difficult to produce, but as processes improved the printing methods developed from the semiconductor industry replaced the mechanical complexity of the PALC cell. PALC is no longer being actively developed.
or LED
in modern systems, shines white light through the cells. By changing the opacity of the cells, differing quantities of RGB light are produced at any one triplet of cells, producing a single color as seen by the eye. The main problem with producing such a display is the need to individually address the enormous number of cells; in a modern high definition television with a 1080p display, this requires 1080 rows of 1920 triplet cells per row, or 6,220,800 individual LCD cells.
PALC displays attempted to address this problem by introducing an intermediate area between the backlight and the LCD on top that used plasma techniques as a "switch". Instead of using individual cells, the display was arranged as a series of rows of LCDs, arranged in an RGB pattern. Beneath the LCD, and above the backlight, was a plasma display consisting of columns of anodes. A clear conductive cathode was positioned above every LCD row.
To produce a display, the system powered each row of the cathodes in turn, along with lit anodes in the plasma layer. This produced a field between the anodes in the columns and cathodes on the rows, producing individually addressed cells. A small amount of ionized gas is pushed towards the LCD in the cells that are powered, creating a small charged spot just below the LCD layer. This switches the LCD, and the amount of power controls the resulting opacity. Cells had to be "erased" to re-draw, by passing a high negative voltage through the cell to push the gas off the LCD layer.
Color television
Color television is part of the history of television, the technology of television and practices associated with television's transmission of moving images in color video....
display technology developed by Tektronix
Tektronix
Tektronix, Inc. is an American company best known for its test and measurement equipment such as oscilloscopes, logic analyzers, and video and mobile test protocol equipment. In November 2007, Tektronix became a subsidiary of Danaher Corporation....
and Sony
Sony
, commonly referred to as Sony, is a Japanese multinational conglomerate corporation headquartered in Minato, Tokyo, Japan and the world's fifth largest media conglomerate measured by revenues....
in the 1990s. PALC displays combine rows formed from liquid crystals
Liquid crystal display
A liquid crystal display is a flat panel display, electronic visual display, or video display that uses the light modulating properties of liquid crystals . LCs do not emit light directly....
with columns formed from plasma cells
Plasma display
A plasma display panel is a type of flat panel display common to large TV displays or larger. They are called "plasma" displays because the technology utilizes small cells containing electrically charged ionized gases, or what are in essence chambers more commonly known as fluorescent...
, the later replacing the transistorized switching in a conventional LCD. Although PALC was successfully developed, thin-film transistor
Thin-film transistor
A thin-film transistor is a special kind of field-effect transistor made by depositing thin films of a semiconductor active layer as well as the dielectric layer and metallic contacts over a supporting substrate. A common substrate is glass, since the primary application of TFTs is in liquid...
based LCD devices improved to offset PALC's advantages, and PALC development has been largely abandoned since the early 2000s.
History
PALC was originally developed by Thomas Buzak, who worked at TektronixTektronix
Tektronix, Inc. is an American company best known for its test and measurement equipment such as oscilloscopes, logic analyzers, and video and mobile test protocol equipment. In November 2007, Tektronix became a subsidiary of Danaher Corporation....
in the U.S. Through the late 1980s and early 1990s he developed and patented a number of concepts that used plasma
Plasma (physics)
In physics and chemistry, plasma is a state of matter similar to gas in which a certain portion of the particles are ionized. Heating a gas may ionize its molecules or atoms , thus turning it into a plasma, which contains charged particles: positive ions and negative electrons or ions...
to provide a switching element for a variety of uses. When the project he was working on was canceled, he turned his attention to using the plasma elements as LCD switches, and the PALC system was born.
In 1993 Tektronix licensed the technology to Sony
Sony
, commonly referred to as Sony, is a Japanese multinational conglomerate corporation headquartered in Minato, Tokyo, Japan and the world's fifth largest media conglomerate measured by revenues....
, and together they started development of the Plasmatron televisions. In October 1996 Sony entered a three-year arrangement with Sharp Electronics to share development, with Sharp's role being to help improve the effective display angles. In July 1997 the group was joined by Philips Electronics to improve the resolution of the devices, reduce power consumption and increase brightness. Sony and Sharp both produced high-definition television
High-definition television
High-definition television is video that has resolution substantially higher than that of traditional television systems . HDTV has one or two million pixels per frame, roughly five times that of SD...
prototypes using the PALC technology, but these never made it to production.
PALC was offset by the rapid introduction of thin-film transistor
Thin-film transistor
A thin-film transistor is a special kind of field-effect transistor made by depositing thin films of a semiconductor active layer as well as the dielectric layer and metallic contacts over a supporting substrate. A common substrate is glass, since the primary application of TFTs is in liquid...
s, which allowed individual cells of the LCD to be addressed directly. A grid of rows and columns allows the transistors to be turned on or off just like the plasma cells, but without the need for high voltages or resetting pulse. At first these devices were difficult to produce, but as processes improved the printing methods developed from the semiconductor industry replaced the mechanical complexity of the PALC cell. PALC is no longer being actively developed.
Description
A conventional LCD display consists of a grid of individual LCD "cells" with red, green or blue (RGB) colored filters in front of them. A back light source, typically a fluorescent lampFluorescent lamp
A fluorescent lamp or fluorescent tube is a gas-discharge lamp that uses electricity to excite mercury vapor. The excited mercury atoms produce short-wave ultraviolet light that then causes a phosphor to fluoresce, producing visible light. A fluorescent lamp converts electrical power into useful...
or LED
LEd
LEd is a TeX/LaTeX editing software working under Microsoft Windows. It is a freeware product....
in modern systems, shines white light through the cells. By changing the opacity of the cells, differing quantities of RGB light are produced at any one triplet of cells, producing a single color as seen by the eye. The main problem with producing such a display is the need to individually address the enormous number of cells; in a modern high definition television with a 1080p display, this requires 1080 rows of 1920 triplet cells per row, or 6,220,800 individual LCD cells.
PALC displays attempted to address this problem by introducing an intermediate area between the backlight and the LCD on top that used plasma techniques as a "switch". Instead of using individual cells, the display was arranged as a series of rows of LCDs, arranged in an RGB pattern. Beneath the LCD, and above the backlight, was a plasma display consisting of columns of anodes. A clear conductive cathode was positioned above every LCD row.
To produce a display, the system powered each row of the cathodes in turn, along with lit anodes in the plasma layer. This produced a field between the anodes in the columns and cathodes on the rows, producing individually addressed cells. A small amount of ionized gas is pushed towards the LCD in the cells that are powered, creating a small charged spot just below the LCD layer. This switches the LCD, and the amount of power controls the resulting opacity. Cells had to be "erased" to re-draw, by passing a high negative voltage through the cell to push the gas off the LCD layer.
Patents
- U.S. Patent 4,864,538, "Method and apparatus for addressing optical data storage locations", Thomas Buzak/Tektronix, filed 5 May 1988, issued 5 September 1989
- U.S. Patent 5,036,317, "Flat panel apparatus for addressing optical data storage locations", Thomas Buzak/Tektronix, filed 22 August 1988, issued 30 July 1991
Further reading
- Thomas S. Buzak, "A New Active-Matrix Technique Using Plasma Addressing", Journal of the Society for Information Display, 1990, pp. 420-423
- Thomas S. Buzak, "Plasma Addressed Liquid Crystal (PALC), A New Flat Panel Technology for Full-Color Video", Tektronix Inc, Paper 9-036, AES 9th International Conference (February 1991)