Editing Liquid-crystal display (section)

==Passive-matrix==
[[File:BBC STN Matrixanzeige 540x270.jpg|thumb|Prototype of a passive-matrix STN-LCD with 540×270 pixels, Brown Boveri Research, Switzerland, 1984]]

Monochrome and later color [[Passive matrix addressing|passive-matrix]] LCDs were standard in most early laptops (although a few used plasma displays<ref>{{Cite web| title=Compaq Portable III| access-date=July 20, 2015| url=http://oldcomputermuseum.com/compaq_lunchbox.html| archive-date=January 2, 2015| archive-url=https://web.archive.org/web/20150102205057/http://www.oldcomputermuseum.com/compaq_lunchbox.html| url-status=live}}</ref><ref>{{Cite AV media| people=Eric Wasatonicundefined (Director)| title=IBM PS/2 P70 Portable Computer&nbsp;— Vintage PLASMA Display}}</ref>) and the original Nintendo [[Game Boy]]<ref name="Game Boy screen type">{{cite web|url=https://www.flickr.com/photos/30348074@N00/5439992398/in/set-72157626034398554/|title=Game Boy: User Manual, page 12|access-date=February 12, 2011|date=February 12, 2011|archive-date=June 29, 2011|archive-url=https://web.archive.org/web/20110629131839/http://www.flickr.com/photos/30348074@N00/5439992398/in/set-72157626034398554/|url-status=live}}</ref> until the mid-1990s, when color [[active matrix|active-matrix]] became standard on all laptops. The commercially unsuccessful [[Macintosh Portable]] (released in 1989) was one of the first to use an active-matrix display (though still monochrome). Passive-matrix LCDs are still used in the 2010s for applications less demanding than laptop computers and TVs, such as inexpensive calculators. In particular, these are used on portable devices where less information content needs to be displayed, lowest power consumption (no [[backlight]]) and low cost are desired or readability in direct sunlight is needed.

[[File:Passive Matrix vs Active Matrix.jpg|thumb|A comparison between a blank passive-matrix display (top) and a blank active-matrix display (bottom). A passive-matrix display can be identified when the blank background is more grey in appearance than the crisper active-matrix display, fog appears on all edges of the screen, and while pictures appear to be fading on the screen.]]

Displays having a passive-matrix structure use ''[[super-twisted nematic]]'' STN (invented by Brown Boveri Research Center, Baden, Switzerland, in 1983; scientific details were published<ref>T.J. Scheffer and J. Nehring,"A new highly multiplexable LCD," Appl. Phys. Lett., vol. 48, no. 10, pp. 1021–1023, Nov. 1984.</ref>) or double-layer STN (DSTN) technology (the latter of which addresses a color-shifting problem with the former), and color-STN (CSTN), in which color is added by using an internal color filter. STN LCDs have been optimized for passive-matrix addressing. They exhibit a sharper threshold of the contrast-vs-voltage characteristic than the original TN LCDs. This is important, because pixels are subjected to partial voltages even while not selected. [[LCD crosstalk|Crosstalk]] between activated and non-activated pixels has to be handled properly by keeping the RMS voltage of non-activated pixels below the threshold voltage as discovered by [[Peter J. Wild]] in 1972,<ref>P. J. Wild, ''Matrix-addressed liquid crystal projection display,'' Digest of Technical Papers, International Symposium, Society for Information Display, June 1972, pp. 62–63.</ref> while activated pixels are subjected to voltages above threshold (the voltages according to the "Alt & Pleshko" drive scheme).<ref>P. M. Alt, P. Pleshko ''Scanning limitations of liquid-crystal displays,'' IEEE Trans. Electron Devices, vol. ED-21, pp. 146–155, February 1974.</ref> Driving such STN displays according to the Alt & Pleshko drive scheme require very high line addressing voltages. Welzen and de Vaan invented an alternative drive scheme (a non "Alt & Pleshko" drive scheme) requiring much lower voltages, such that the STN display could be driven using low voltage CMOS technologies.<ref name="EP0221613B1" /> White-on-blue LCDs are STN and can use a blue polarizer, or birefringence which gives them their distinctive appearance.<ref>{{cite book | url=https://books.google.com/books?id=zmlQDwAAQBAJ&dq=lcd+blue+polarizer&pg=PA187 | isbn=978-1-4822-4181-5 | title=Handbook of Optoelectronics: Enabling Technologies (Volume Two) | date=October 6, 2017 | publisher=CRC Press }}</ref><ref>{{cite book | url=https://books.google.com/books?id=TglEDwAAQBAJ&dq=blue+mode+birefringence&pg=SA97-PA14 | title=Measurement, Instrumentation, and Sensors Handbook: Electromagnetic, Optical, Radiation, Chemical, and Biomedical Measurement | isbn=978-1-351-83333-2 | last1=Webster | first1=John G. | last2=Eren | first2=Halit | date=December 19, 2017 | publisher=CRC Press }}</ref><ref>{{Cite journal |url=https://pubs.aip.org/aip/apl/article-abstract/45/10/1021/50395/A-new-highly-multiplexable-liquid-crystal-display |title=A new, highly multiplexable liquid crystal display |journal=Applied Physics Letters |date=November 15, 1984 |volume=45 |issue=10 |pages=1021–1023 |doi=10.1063/1.95048 |access-date=January 23, 2024 |archive-date=January 23, 2024 |archive-url=https://web.archive.org/web/20240123225211/https://pubs.aip.org/aip/apl/article-abstract/45/10/1021/50395/A-new-highly-multiplexable-liquid-crystal-display |url-status=live |last1=Scheffer |first1=T. J. |last2=Nehring |first2=J. |bibcode=1984ApPhL..45.1021S }}</ref>

STN LCDs have to be continuously refreshed by alternating pulsed voltages of one polarity during one frame and pulses of opposite polarity during the next frame. Individual pixels are [[Display addressing scheme|addressed]] by the corresponding row and column circuits. This type of display is called ''[[Passive matrix addressing|passive-matrix addressed]]'', because the pixel must retain its state between refreshes without the benefit of a steady electrical charge. As the number of pixels (and, correspondingly, columns and rows) increases, this type of display becomes less feasible. Slow [[response time (technology)|response time]]s and poor [[Display contrast|contrast]] are typical of passive-matrix addressed LCDs with too many pixels and driven according to the "Alt & Pleshko" drive scheme. Welzen and de Vaan also invented a non RMS drive scheme enabling to drive STN displays with video rates and enabling to show smooth moving video images on an STN display.{{cn|date=November 2023}} Citizen, among others, licensed these patents and successfully introduced several STN based LCD pocket televisions on the market.{{cn|date=November 2023}}

[[File:Lcd-engineerguy.ogv|thumb|How an LCD works using an active-matrix structure]]

Bistable LCDs do not require continuous refreshing. Rewriting is only required for picture information changes. In 1984 HA van Sprang and AJSM de Vaan invented an STN type display that could be operated in a bistable mode, enabling extremely high resolution images up to 4000 lines or more using only low voltages.<ref>[https://worldwide.espacenet.com/publicationDetails/originalDocument?FT=D&date=19870512&DB=EPODOC&locale=en_EP&CC=US&NR=4664483A&KC=A&ND=5# Liquid Crystal Display Device with a hysteresis] {{Webarchive|url=https://web.archive.org/web/20210308072333/https://worldwide.espacenet.com/publicationDetails/originalDocument?FT=D&date=19870512&DB=EPODOC&locale=en_EP&CC=US&NR=4664483A&KC=A&ND=5 |date=March 8, 2021 }}, HA van Sprang and AJSM de Vaan; European patent: EP0155033B1; January 31, 1990; filed February 24, 1984; https://worldwide.espacenet.com/publicationDetails/biblio?CC=EP&NR=0155033B1&KC=B1&FT=D&ND=4&date=19900131&DB=EPODOC&locale=en_EP# {{Webarchive|url=https://web.archive.org/web/20210313041403/https://worldwide.espacenet.com/publicationDetails/biblio?CC=EP&NR=0155033B1&KC=B1&FT=D&ND=4&date=19900131&DB=EPODOC&locale=en_EP |date=March 13, 2021 }}; US patent US4664483A</ref> Since a pixel may be either in an on-state or in an off state at the moment new information needs to be written to that particular pixel, the addressing method of these bistable displays is rather complex, a reason why these displays did not make it to the market. That changed when in the 2010 "zero-power" (bistable) LCDs became available. Potentially, passive-matrix addressing can be used with devices if their write/erase characteristics are suitable, which was the case for ebooks which need to show still pictures only. After a page is written to the display, the display may be cut from the power while retaining readable images. This has the advantage that such ebooks may be operated for long periods of time powered by only a small battery.

High-[[display resolution|resolution]] color displays, such as modern LCD [[computer monitor]]s and televisions, use an [[Active matrix|active-matrix]] structure. A matrix of [[thin-film transistor]]s (TFTs) is added to the electrodes in contact with the LC layer. Each pixel has its own dedicated [[transistor]], allowing each column line to access one pixel. When a row line is selected, all of the column lines are connected to a row of pixels and voltages corresponding to the picture information are driven onto all of the column lines. The row line is then deactivated and the next row line is selected. All of the row lines are selected in sequence during a [[Refresh rate|refresh]] operation. Active-matrix addressed displays look brighter and sharper than passive-matrix addressed displays of the same size, and generally have quicker response times, producing much better images. Sharp produces bistable reflective LCDs with a 1-bit SRAM cell per pixel that only requires small amounts of power to maintain an image.<ref>{{Cite web|url=https://www.sharpsma.com/products?sharpCategory=Memory+LCD&p_p_parallel=0|title=Products - Sharp|website=www.sharpsma.com|access-date=December 25, 2019|archive-date=January 18, 2020|archive-url=https://web.archive.org/web/20200118061852/https://www.sharpsma.com/products?sharpCategory=Memory+LCD&p_p_parallel=0|url-status=dead}}</ref>

[[Segment LCD]]s can also have color by using Field Sequential Color (FSC LCD). This kind of displays have a high speed passive segment LCD panel with an RGB backlight. The backlight quickly changes color, making it appear white to the naked eye. The LCD panel is synchronized with the backlight. For example, to make a segment appear red, the segment is only turned ON when the backlight is red, and to make a segment appear magenta, the segment is turned ON when the backlight is blue, and it continues to be ON while the backlight becomes red, and it turns OFF when the backlight becomes green. To make a segment appear black, the segment is always turned ON. An FSC LCD divides a color image into 3 images (one Red, one Green and one Blue) and it displays them in order. Due to [[persistence of vision]], the 3 monochromatic images appear as one color image. An FSC LCD needs an LCD panel with a refresh rate of 180&nbsp;Hz, and the response time is reduced to just 5 milliseconds when compared with normal STN LCD panels which have a response time of 16 milliseconds.<ref>[http://www.orientdisplay.com/pdf/ProductPresentation-FS-LCD.pdf Product presentation] {{Webarchive|url=https://web.archive.org/web/20210225093828/http://www.orientdisplay.com/pdf/ProductPresentation-FS-LCD.pdf |date=February 25, 2021 }}</ref><ref>{{Cite web|url=https://www.mbtmag.com/article/2012/02/advantages-field-sequential-color-technology|archive-url=https://web.archive.org/web/20160602012543/https://www.mbtmag.com/article/2012/02/advantages-field-sequential-color-technology|url-status=dead|archive-date=June 2, 2016|title=The Advantages To Field Sequential Color Technology|date=June 2, 2016}}</ref> FSC LCDs contain a Chip-On-Glass driver IC can also be used with a capacitive touchscreen. This technique can also be applied in displays meant to show images, as it can offer higher light transmission and thus potential for reduced power consumption in the backlight due to omission of color filters in LCDs.<ref>{{cite web | url=https://phys.org/news/2005-10-samsung-world-largest-lcd-panel.amp | title=Samsung Develops World's Largest (32<nowiki>''</nowiki>) LCD Panel Without a Color Filter }}</ref>

Samsung introduced UFB (Ultra Fine & Bright) displays back in 2002, utilized the super-birefringent effect. It has the luminance, color gamut, and most of the contrast of a TFT-LCD, but only consumes as much power as an STN display, according to Samsung. It was being used in a variety of Samsung cellular-telephone models produced until late 2006, when Samsung stopped producing UFB displays. UFB displays were also used in certain models of LG mobile phones.