# Passive matrix addressing

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{{Short description|Addressing scheme for LCDs}}
'''Passive matrix addressing''' is an [addressing scheme](/source/Display_addressing_scheme) used in early [liquid crystal displays (LCDs)](/source/liquid_crystal_displays). It is a matrix addressing scheme, meaning that only ''m'' + ''n'' control signals are required to address an ''m'' × ''n'' display. A [pixel](/source/pixel) in a passive matrix must maintain its state without active driving circuitry until it can be refreshed again.

The [signal](/source/Wiktionary%3Asignal) is divided into a row or ''select signal'' and a column or ''video signal''.  The select [voltage](/source/voltage) determines the row that is being addressed and all ''n'' pixels on a row are addressed simultaneously. When [pixels](/source/pixels) on a row are being addressed, a ''V<SUB>sel</SUB>'' potential is applied, and all other rows are unselected with a ''V<SUB>unsel</SUB>'' potential. The video signal or column potential is then applied with a potential for each ''m'' columns individually. An on-switched (lit) [pixel](/source/pixel) corresponds to a ''V<SUB>on</SUB>'', an off-switched (unlit) corresponds to a ''V<SUB>off</SUB>'' potential.<ref>{{cite web |url=http://ethw.org/First-Hand:Liquid_Crystal_Display_Evolution_-_Swiss_Contributions#Venture:_BBC_&amp;_ROCHE|title=First-Hand Histories: Liquid Crystal Display Evolution - Swiss Contributions |work=Engineering and Technology History Wiki |publisher=ETHW |last1=Wild|first1=Peter J|accessdate=June 30, 2017}}</ref>

The potential across [pixel](/source/pixel) at selected row ''i'' and column ''j'' is
:<math>V_{ij} = V_\mathit{sel} - V_\mathit{on|off}</math>
and
:<math>V_{ij} = V_\mathit{unsel} - V_\mathit{on|off}</math>
for the unselected rows.<ref>P. M. Alt, P. Pleshko ''Scanning limitations of liquid-crystal displays,'' IEEE Trans. Electron Devices, vol. ED-21, pp. 146–155, Feb. 1974.</ref>

This scheme has been expanded to define the limits of this type of addressing typical LCDs.<ref>J. Nehring, A. R. Kmetz: [https://ieeexplore.ieee.org/document/1480073 ''Ultimate limits for matrix addressing of RMS-responding liquid-crystal displays.''] IEEE Transactions on Electron Devices. Vol. 26, issue 5, pp. 795–802, May 1979.</ref><ref>T. N. Ruckmongathan, V. Arun, Babu Hemanth Kumar: [https://ieeexplore.ieee.org/document/4356461 ''Line-by-Line Addressing of RMS Responding Matrix Displays With Wavelets.''] Journal of Display Technology. Vol. 3, issue 4, pp. 413–420 December 2007.</ref>

Passive matrix addressed displays, such as [ferroelectric liquid crystal display](/source/ferroelectric_liquid_crystal_display)s, do not need the switch component of an active matrix display, because they have built-in [bistability](/source/bistability). Technology for [electronic paper](/source/electronic_paper) also has a form of bistability. Displays with bistable pixel elements are addressed with a passive matrix addressing scheme, whereas [TFT LCD](/source/Thin-film-transistor_liquid-crystal_display) displays are addressed using [active addressing](/source/active_matrix_addressing).

==See also==
* [Active matrix addressing](/source/Active_matrix_addressing)
* [Pixel geometry](/source/Pixel_geometry)
* [Liquid crystal display](/source/Liquid_crystal_display)

==References==
<references />

{{DEFAULTSORT:Passive Matrix Addressing}}
Category:Digital imaging
Category:Liquid crystal displays

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Adapted from the Wikipedia article [Passive matrix addressing](https://en.wikipedia.org/wiki/Passive_matrix_addressing) by Wikipedia contributors ([contributor history](https://en.wikipedia.org/wiki/Passive_matrix_addressing?action=history)). Available under [Creative Commons Attribution-ShareAlike 4.0 International](https://creativecommons.org/licenses/by-sa/4.0/). Changes may have been made.