Editing Touchscreen (section)

===Capacitive touchscreen===
[[File:Capacitive touchscreen.jpg|thumb|Capacitive touchscreen of a mobile phone]]
[[File:Casio TC500 Touch Sensor Watch.jpg|thumb|The Casio TC500 Capacitive touch sensor watch from 1983, with angled light exposing the touch sensor pads and traces etched onto the top watch glass surface]]
{{Main|Capacitive sensing}}

A capacitive touchscreen panel consists of an [[insulator (electrical)|insulator]], such as [[glass]], coated with a transparent [[electrical conductor|conductor]], such as [[indium tin oxide]] (ITO).<ref>{{cite journal |last1=Hong |first1=Chan-Hwa |last2=Shin |first2=Jae-Heon |last3=Ju |first3=Byeong-Kwon |last4=Kim |first4=Kyung-Hyun |last5=Park |first5=Nae-Man |last6=Kim |first6=Bo-Sul |last7=Cheong |first7=Woo-Seok |title=Index-Matched Indium Tin Oxide Electrodes for Capacitive Touch Screen Panel Applications |journal=Journal of Nanoscience and Nanotechnology |date=1 November 2013 |volume=13 |issue=11 |pages=7756–7759 |doi=10.1166/jnn.2013.7814 |pmid=24245328 |s2cid=24281861 }}</ref> As the human body is also an electrical conductor, touching the surface of the screen results in a distortion of the screen's [[electrostatic]] field, measurable as a change in [[capacitance]]. Different technologies may be used to determine the location of the touch. The location is then sent to the controller for processing. Some touchscreens use silver instead of ITO, as ITO causes several environmental problems due to the use of indium.<ref>{{cite web|url=https://www.fujifilm.eu/eu/news/article/fujifilm-reinforces-the-production-facilities-for-its-touch-panel-sensor-film-exclear|title=Fujifilm reinforces the production facilities for its touch-panel sensor film "EXCLEAR"|website=FUJIFILM Europe}}</ref><ref>{{cite web|url=https://www.fujifilm.com/about/research/report/062/pdf/index/ff_rd062_008_en.pdf |title=Development of a Thin Double-sided Sensor Film "EXCLEAR" for Touch Panels via Silver Halide Photographic Technology |publisher=www.fujifilm.com |access-date=2019-12-09}}</ref><ref>{{cite web|url=https://fujifilm-innovation.tumblr.com/post/142053562369/whats-behind-your-smartphone-screen-this|title=What's behind your smartphone screen? This... &#124;|website=fujifilm-innovation.tumblr.com}}</ref><ref>{{cite web|url=https://www.fujifilmholdings.com/en/sustainability/valuePlan2016/process/policy01/environment2016/02.html|title=Environment: [Topics2] Development of Materials That Solve Environmental Issues EXCLEAR thin double-sided sensor film for touch panels &#124; FUJIFILM Holdings|website=www.fujifilmholdings.com}}</ref> The controller is typically a [[complementary metal–oxide–semiconductor]] (CMOS) [[application-specific integrated circuit]] (ASIC) chip, which in turn usually sends the signals to a CMOS [[digital signal processor]] (DSP) for processing.<ref>{{cite journal |last1=Kent |first1=Joel |title=Touchscreen technology basics & a new development |journal=CMOS Emerging Technologies Conference |date=May 2010 |volume=6 |pages=1–13 |url=https://books.google.com/books?id=ekdkWGqw29EC&pg=PA34 |publisher=CMOS Emerging Technologies Research|isbn=9781927500057 }}</ref><ref>{{cite news |last1=Ganapati |first1=Priya |title=Finger Fail: Why Most Touchscreens Miss the Point |url=https://www.wired.com/2010/03/touchscreens-smartphones/ |access-date=9 November 2019 |magazine=[[Wired (magazine)|Wired]] |date=5 March 2010 |archive-url=https://web.archive.org/web/20140511114207/http://www.wired.com/2010/03/touchscreens-smartphones/ |archive-date=2014-05-11 |url-status=live}}</ref>

Unlike a [[resistive touchscreen]], some capacitive touchscreens cannot be used to detect a finger through electrically insulating material, such as gloves. This disadvantage especially affects usability in consumer electronics, such as touch tablet PCs and capacitive smartphones in cold weather when people may be wearing gloves. It can be overcome with a special capacitive stylus, or a special-application glove with an embroidered patch of conductive thread allowing electrical contact with the user's fingertip.

A low-quality [[switching-mode power supply]] unit with an accordingly unstable, noisy [[voltage]] may temporarily interfere with the precision, accuracy and sensitivity of capacitive touch screens.<ref>{{Cite web|last=Andi|date=2014-01-24|title=How noise affects touch screens|url=https://www.westfloridacomponents.com/blog/noise-affects-touch-screens/|access-date=2020-10-24|website=West Florida Components|language=en-US}}</ref><ref>{{cite web |title=Touch screens and charger noise {{!}} |url=https://www.epanorama.net/blog/2013/03/12/touch-screens-and-charger-noise/ |website=epanorama.net |date=2013-03-12}}</ref><ref>{{cite web |title=Aggressively combat noise in capacitive touch applications |url=https://www.edn.com/aggressively-combat-noise-in-capacitive-touch-applications/ |website=EDN.com |date=2013-04-08}}</ref>

Some capacitive display manufacturers continue to develop thinner and more accurate touchscreens. Those for [[mobile device]]s are now being produced with 'in-cell' technology, such as in Samsung's [[AMOLED#Super AMOLED|Super AMOLED]] screens, that eliminates a layer by building the capacitors inside the display itself. This type of touchscreen reduces the visible distance between the user's finger and what the user is touching on the screen, reducing the thickness and weight of the display, which is desirable in [[smartphone]]s.

A simple parallel-plate capacitor has two conductors separated by a dielectric layer. Most of the energy in this system is concentrated directly between the plates. Some of the energy spills over into the area outside the plates, and the electric field lines associated with this effect are called fringing fields. Part of the challenge of making a practical capacitive sensor is to design a set of printed circuit traces which direct fringing fields into an active sensing area accessible to a user. A parallel-plate capacitor is not a good choice for such a sensor pattern. Placing a finger near fringing electric fields adds conductive surface area to the capacitive system. The additional charge storage capacity added by the finger is known as finger capacitance, or CF. The capacitance of the sensor without a finger present is known as parasitic capacitance, or CP.

====Surface capacitance====
In this basic technology, only one side of the insulator is coated with a conductive layer. A small voltage is applied to the layer, resulting in a uniform electrostatic field. When a conductor, such as a human finger, touches the uncoated surface, a capacitor is dynamically formed. The sensor's controller can determine the location of the touch indirectly from the change in the capacitance as measured from the four corners of the panel. As it has no moving parts, it is moderately durable but has limited resolution, is prone to false signals from parasitic [[capacitive coupling]], and needs [[calibration]] during manufacture. It is therefore most often used in simple applications such as industrial controls and [[interactive kiosk|kiosks]].<ref>{{cite web|url=http://electronicdesign.com/Articles/Index.cfm?AD=1&ArticleID=18592|title=Please Touch! Explore The Evolving World Of Touchscreen Technology|publisher=electronicdesign.com|access-date=2009-09-02|url-status=dead|archive-url=https://web.archive.org/web/20151213043947/http://electronicdesign.com/Articles/Index.cfm?AD=1&ArticleID=18592|archive-date=2015-12-13}}</ref>

Although some standard capacitance detection methods are projective, in the sense that they can be used to detect a finger through a non-conductive surface, they are very sensitive to fluctuations in temperature, which expand or contract the sensing plates, causing fluctuations in the capacitance of these plates.<ref>{{cite web|url=https://www.electronics-tutorials.ws/capacitor/cap_4.html|title=formula for relationship between plate area and capacitance|date=26 July 2013 }}</ref> These fluctuations result in a lot of background noise, so a strong finger signal is required for accurate detection. This limits applications to those where the finger directly touches the sensing element or is sensed through a relatively thin non-conductive surface.

==== Mutual capacitance ====
An electrical signal, imposed on one electrical conductor, can be capacitively "sensed" by another electrical conductor that is in very close proximity, but electrically isolated—a feature that is exploited in mutual capacitance touchscreens. In a mutual capacitive sensor array, the "mutual" crossing of one electrical conductor with another electrical conductor, but with no direct electrical contact, forms a [[capacitor]] (see [[touchscreen#Construction]]).

High frequency voltage pulses are applied to these conductors, one at a time. These pulses capacitively couple to every conductor that intersects it.

Bringing a finger or conductive stylus close to the surface of the sensor changes the local electrostatic field, which in turn reduces the capacitance between these intersecting conductors. Any significant change in the strength of the signal sensed is used to determine if a finger is present or not at an intersection.<ref>{{cite web|url=https://onlinedocs.microchip.com/pr/GUID-A8A0085D-58D1-4E41-A07D-B93BFDE11AFE-en-US-4/index.html?GUID-F186B556-F266-4585-830D-1CCE04045D0E|title=Mutual Capacitance|access-date=2023-04-26}}</ref>

The capacitance change at every intersection on the grid can be measured to accurately determine one or more touch locations.
 
Mutual capacitance allows multi-touch operation where multiple fingers, palms or styli can be accurately tracked at the same time.The greater the number of intersections, the better the touch resolution and the more independent fingers that can be detected.<ref>{{cite web|url=https://walkermobile.com/Touch_Technologies_Tutorial_Latest_Version.pdf|title=Touch technologies|access-date=2023-04-26}}</ref>
<ref>{{cite web|url=https://fieldscale.com/learn-capacitive-sensing/self-mutual-capacitive-touch-sensors/|title=Self vs Mutual Capacitance|work=Fieldscale |access-date=2023-04-26}}</ref> This indicates a distinct advantage of diagonal wiring over standard x/y wiring, since diagonal wiring creates nearly twice the number of intersections.

A 30 i/o, 16×14 x/y array, for example, would have 224 of these intersections / capacitors, and a 30 i/o diagonal lattice array could have 435 intersections.

Each trace of an x/y mutual capacitance array only has one function, it is either an input or an output. The horizontal traces may be transmitters while the vertical traces are sensors, or vice versa.

==== Self-capacitance ====
Self-capacitance sensors can have the same layout as mutual capacitance sensors, but, with self-capacitance all the traces usually operate independently, with no interaction between different traces. Along with several other methods, the extra capacitive load of a finger on a trace electrode may be measured by a current meter, or by the change in frequency of an RC oscillator.

Traces are sensed, one after the other until all the traces have been sensed. A finger may be detected anywhere along the whole length of a trace (even "off-screen"), but there is no indication where the finger is along that trace. If, however, a finger is also detected along another intersecting trace, then it is assumed that the finger position is at the intersection of the two traces. This allows for the speedy and accurate detection of a single finger.

Although mutual capacitance is simpler for multi-touch, multi-touch can be achieved using self-capacitance.

Self-capacitive touch screen layers are used on mobile phones such as the [[Sony Xperia Sola]],<ref name="SonyDev">{{Cite web |url=http://developer.sonymobile.com/wp/2012/03/13/imagine-controlling-your-phone-without-touching-the-screen-floating-touch-makes-it-possible-video/ |title=Self-capacitive touch described on official Sony Developers blog |access-date=2012-03-14 |archive-date=2012-03-14 |archive-url=https://archive.today/20120314110416/http://developer.sonymobile.com/wp/2012/03/13/imagine-controlling-your-phone-without-touching-the-screen-floating-touch-makes-it-possible-video/ |url-status=live }}</ref> the [[Samsung Galaxy S4]], [[Galaxy Note 3]], [[Galaxy S5]], and [[Galaxy Alpha]].

Self-capacitance is far more sensitive than mutual capacitance and is mainly used for single touch, simple gesturing and proximity sensing where the finger does not even have to touch the glass surface. Mutual capacitance is mainly used for multitouch applications.<ref>{{cite journal|title=Comparison of self capacitance and mutual capacitance. |doi=10.1017/S1743921315010388 |arxiv=1612.08227 |last1=Du |first1=Li |year=2016 |s2cid=220453196 }}</ref> Many touchscreen manufacturers use both self and mutual capacitance technologies in the same product, thereby combining their individual benefits.<ref>{{cite web|url=http://www.cypress.com/products/cypress-sensing-technologies|title=Hybrid self and mutual capacitance touch sensing controllers }}</ref>

====Use of stylus on capacitive screens====
Capacitive touchscreens do not necessarily need to be operated by a finger, but until recently the special styli required could be quite expensive to purchase. The cost of this technology has fallen greatly in recent years and capacitive styli are now widely available for a nominal charge, and often given away free with mobile accessories. These consist of an electrically conductive shaft with a soft conductive rubber tip, thereby resistively connecting the fingers to the tip of the stylus.