Electronics

MOBILE PHONE BATTERY

Battery is the power source of Mobile phone.which produces electric energy by means of chemical reaction.Terminal voltage of a mobile phone battery is 3.7v. Mobile phone batteries are coming under the category of  secondary cells,which means they are rechargeable.

 According to the chemical combination,there are several types batteries used in mobile phone.they are..

1. NiCd   : Nickel Cadmium batteries
2. NiMH : Nickel Metal Hydroxide batteries
3. Li-ione : Lithium Ione batteries
4. Li-Polymer : Lithium Polymer batteries

 How ever , in recent mobile phones uses Li-Ione or Li-polymer batteries.

Memory effect in batteries

  As we recharge the battery frequently with out allowing to discharge  the stored charge fully,the unused portion of the battery will be permanently become damaged and backup capacity of the battery will be reduced this is known as Memory effect of battery.Li-ione and Li-polymer batteries has very less memory effect.

Terminals of Mobile phone Battery

Basically a mobile phone battery has three terminals.in some case there will be 4 terminals also..they are 

1. Battery positive (+ve)
2. Battery Negative (-ve)
3. BSI (Battery Size Indicators)
4. BTEMP (Battery temperature)

BSI : this terminal gives current status the amount charge in the battery.also it helps the mobile device to detect whether it is a specified battery  for it,it gives protection damages due to  accidental removal of the battery .since all these factors,there may be complaints in mobile device due to faulty or non specified batteries

COMPLAINTS DUE TO BSI TERMINALS

• Not switching on
• Restarting issue
• SIM card not detecting issue
• Automatic switching off issue.
• Charging related issue(error messages like "battery disconnected"
• Test mode/local mode issue

BTEMP : this terminals gives  the temperature of the battery while the battery being recharged.It is achieved by means of a NTC type thermister(negative temperature coefficient type) .some time this thermister will be in mother board,in such case battery will not have the btemp terminal.

COMPLAINTS DUE TO BTEMP TERMINAL

• charging issue with error message "charging paused,battery temperature too high"
• charging issue with error message "charging paused,battery temperature too low"

NFC Terminal: In some batteries ,the fourth terminals may be dedicated for the NFC (Near Field Communication)antenna eg: SAMSUNG Galaxy S3

SPECIFICATIONS OF MOBILE PHONE BATTERIES

• Battery Type
• current delivering capacity (in mAH : milli ampere per hour)

PRECAUTIONS FOR BATTERY USAGE

DANGER !!

 Disassemble and Reconstruction “Do not disassemble or reconstruct battery” The battery pack has safety function and protection circuit to avoid the danger. If they have serous damage, it will cause .the generating heat, smoke, rupture or flame.

2. Short-circuit “Don not short-circuit battery cell Do not connect + and – terminals with metals (such as wire). Do not carry or store the battery cell with metal objects (such as wire, or hairpins). If the battery cell is short-circuited excessive large current will flow and then the generating heat, smoke, rupture or flame will occur. And also, it causes generating heat at metals.
3. Incineration and Heating “Do not incinerate or heat the battery cell” These occur the melting of insulator, damage of gas release vent or safety function, or ignition on electrolyte. Above mentioned matters cause the generating heat, smoke, rupture or flame.
 4. Use nearby Heated Place “Do not use or leave battery nearby fire, stove or heated place (more than 80°C)” In case that separator made of polymer is melted by high temperature, the internal short-circuit occurs in individual cells and then it causes the generating heat, smoke, rupture or flame. In addition, do not use the battery cell under the heated place (more than 80°C).
 5. Immersion “Do not immerse the battery in water or sea water, or get it wet” If the protection circuit included in the battery cell is broken, the battery cell will be charged at extreme current or voltage and the abnormal chemical reaction occurs in it. And then it causes the generating heat, smoke, rupture or flame.
 6. Charge nearby Heated Place “Do Not charge battery nearby the fire or under the blazing sun” If the protection circuit to avoid the danger works under high temperature or it is broken, the battery cell will be charged at abnormal current (or voltage) and abnormal chemical reaction will occur. It causes the generating heat, smoke, rupture or flame.
7. Charger and Charge Condition “Do use the specified charger and observe charging requirement” If the battery cell is charged with unspecified condition (under high temperature over the regulated value, excessive high voltage or current over regulated value, or remodeled charger), there are cases that it will be overcharged or the abnormal chemical reaction will occur in cells. It causes the generating heat, smoke, rupture or flame.
 8. Penetration “Don to drive a nail into the battery, stick it by hammer, or tread it” As the battery cell might be broken or deformed and then it will be short-circuited, it causes the generating heat, smoke, rupture or flame.
 9. Impact “Do Not give battery impact or throw it” The impact might cause leakage, heat, smoke, rupture, and/or fire of cell in the battery. And also if the protection circuit in the battery cell is broken, the battery will be charged abnormal voltage or current, and abnormal chemical reaction might occur. It might cause leakage, heat, smoke, rupture, and/or fire.
 10. Deformation “Do not use the battery cell with conspicuous damage or deformation” It causes the generating heat, smoke, rupture or flame.
 11. Soldering “Do not make the direct soldering on battery cell” As the insulator is melted by heat or the gas release vent (or safety function) is broken, it causes the generating heat, smoke, rupture or flame.
 12. Reverse Charge and Over-discharge “Do not reverse polarity (and terminals)” On charging, the battery cell is reverse-charged and abnormal chemical reaction occurs. And also, there may be case that unexpected large current flows on discharging. These cause the generating heat, smoke, rupture or flame.
 13. Reversed Polarity Use “Do not reverse-charge or reverse-connect” The battery cell has polarity. In case the battery cell is not connected with charger or equipment smoothly, do not force them and do check polarity of battery. If the battery cell is connected to opposite polarity with charger, it will be reverse-charged and abnormal chemical reaction will occur. It causes the generating heat, smoke, rupture or flame.
14. Inappropriate Use For Other Equipment “Do not use battery cell for other equipment” If the battery cell is used for unspecified equipment, it will deteriorate its performance and cycle-life. At worst, abnormal current will flow or battery may generate heat, smoke, rupture or flame.
 15. Leakage “Do not touch leaked battery cell” Do not touch your eyes but wash them immediately, and then see a doctor if leaked electrotype is into your eyes. If pay no attention to your eyes, it will cause eye disease.

Warning！

 1. Mixed Use “Do not use lithium ion battery cell in mixture” Do not use lithium ion battery cell with the primary batteries or secondary batteries whose capacity or kinds or maker is different. If do that, the battery cell will be discharged or charged excessively in use. And it may cause the generating heat, smoke, rupture or flame because of the abnormal chemical reaction in cells.

 2. Ingestion “Keep the battery cell away from babies” Keep the little battery cell out of the reach of babies in order to avoid troubles by Swallowing. In case of swallowing the battery, see a doctor immediately.
 3. Charging Time “Do not continue to charge battery cell over specified time” If the battery cell is not finished charging over regulated time, let it stop charging. There is possibility that the battery cell might generate heat, smoke, rupture or flame.
4. Storage “Do not get into a microwave or a high pressure container” It causes the generating heat, smoke, rupture or flame because of a sudden heat or damage of sealing condition of battery cell.
5. Leakage “Do not use a leaked battery cell narby fire” If the liquid leaks from the battery cell (or the battery gives out bad smell), let the battery cell leave from flammable objects immediately. Unless do that, the electrolyte leaked from battery cell will catch fire and it will cause the smoke, flame or rupture of it.
 6. Rust, Charging color and Deformation “Do not use an abnormal battery cell” In case the battery cell has bad smell or is generated its changing color or deformation or causes something wrong in using (includes charging and storage). Let it take out from equipment or charger and do not use it. If an abnormal battery cell is used, it will generate heat, smoke, rupture or flame.

 Caution！

 1. Use under strong sunshine Do not use or leave the battery cell under the blazing sun (or in heated car by sunshine). The battery cell may generate heat, smoke or flame. And also, it might cause the deterioration of battery cell’s characteristics or cycle life.

 2. Static Electricity The battery pack has the protection circuit to avoid the danger. Do not use nearby the place where generates static electricity (more than 100V) which gives damage to the protection circuit. If the protection circuit were broken, the battery cell would hide danger.
3. Charging Temperature Range Charging temperature range is regulated between 0°C and 40°C. Do not charge the battery cell out of recommended temperature range. Charging out of recommended range might cause the generating heat or serous damage of battery cell. And also, if might cause the deterioration of battery cell’s characteristics and cycle life.
 4. Manual Please read the manual before using the battery cell and keep it after reading.
5. Charging method Please read the manual of specified charger about charging method.
6. First time use When the battery cell has rust, bad smell or something abnormal at first-time using, do not use the equipment and go to bring the battery cell to the shop which it was bought.
7. Leakage If the skin or cloth is smeared with liquid form the battery cell, wash with fresh water. It may cause the skin inflammation.  

MORE ABOUT TIZEN

Based on Linux 

Tizen is an open source operating system based on the Linux kernel and WebKit runtime. This means that users can obtain the source code that Tizen is based on, allowing smartphone owners to tinker with and alter a device’s software. Android, Firefox OS and Ubuntu are also open-source, unlike Apple’s closed iOS mobile operating system.

Samsung’s Android Alternative? 

It’s no secret that Samsung’s Android handsets have been widely successful. However, numerous reports have suggested that Samsung has been itching for an OS with more creative control, seeking to wean itself off Google. In a recent interview, Samsung’s own JK Shin told CNET that Tizen is more than just a side project, but also a “simple alternative for Android.”

This doesn’t come as much of a surprise, considering Samsung has been taking steps to add its own brand to the mobile OS on its smartphones. Implementing a relatively unknown OS such as Tizen onto a flagship device like the Galaxy S4 could give Samsung the opportunity decrease reliance on one of its competitors. Samsung smartphones come with a heavily skinned version of Android known as TouchWiz, which puts Samsung’s own spin on the Android interface and includes its own Samsung Apps store.

The App Challenge 

There’s no denying that Samsung and Intel are pushing for developer support for their Tizen platform, especially when the companies are willing to put $4 million toward app creation. As part of the app development challenge, developers have until Nov. 1 to submit apps for the Tizen OS. Judging will take place between Nov. 4 and 5 and the winners will be unveiled in December.

 The developer behind the best game will be awarded $200,000, while the best non-gaming app will receive $120,000. The top 10 HTML 5-based applications will receive $50,000 each, and the total $4.04 million allotment will be spread across nine categories and 50 developers. Tizen’s app page is blank at the moment, but with hundreds of thousands of dollars hanging in the balance we’re interested to see how it grows.

Emphasis on HTML 5

Tizen encourages its developers to write apps in HTML5, which the most recent iteration of the HTML standard that debuted back in 2010. Other operating systems such as Android and iOS use Java and Objective-C as their primary coding languages. HTML5 essentially enables a smoother Web browsing experience for mobile devices, such as the ability to display embedded videos or play music without an additional plugins and save data offline.

Similar to Android Yet Different 

Like most smartphone user interfaces, Tizen’s OS seems to feature core components such as the home screen, notification panel, and lock screen. While the Tizen OS shares some Android design elements, there are also some fundamental differences.

For example, the Tizen home screen displays applications just like an app drawer would, rather than the Android home screen which displays the time and only one row of icons at the bottom of the screen. While the home screen may differ, drop down menus and app menus have the same grayish boxy look as those in Android do. Like Google’s mobile OS, there’s a notification bar that can be accessed by swiping down from the top of the screen. Of course, this is based on a prototype of the Tizen OS that was showcased at Mobile World Congress in Barcelona, so the final design is subject to change.

Multi-Window View, Floating Browsers 

 Based on what we can gather from the app design guidelines posted on Tizen’s developer page, Tizen is likely to come with a multi-window feature similar to the Q Slide feature found on newer LG devices. Essentially, Tizen apps would be able to exist in either “full window” form or a “mini window” mode that would create a “floating browser” effect. Multi window views and floating browsers aren’t new, but they’re certainly not standard smartphone features that come built in to every smartphone’s UI.

At the same time, Tizen’s website details another design aspect dubbed “Multi-window,” which is similar to a feature of the same name found on Samsung smartphones. This feature lets you view apps in a split view. However, unlike the Samsung feature, which runs two apps in separate windows on the screen, Tizen’s version displays one app in a split view. So, for instance, rather than selecting an email to read it, you can enable a split view that shows the body of your email and your inbox at the same time. Similarly, in a music app you could theoretically have the song currently playing displayed next to your playlist without having to navigate back and forth.

Basic Gestures

The Tizen operating system is built to interact with certain touch gestures that consist of taps, swipes and flicks among other actions. As is the case with most touch screen devices, tapping an item will select it and long-pressing will launch an app-specific option menu. Pinch to zoom, dragging and dropping icons, and flicking to quick scroll are all supported within the Tizen UI.

Not Just For Smartphones

Tizen may be touted as Samsung’s new Android alternative, but the truth is the software isn’t made just for mobile devices. At this year’s Mobile World Congress in Barcelona, Intel demonstrated an infotainment system for cars that runs on the Linux-based OS. According to Intel, this system would be able to access Google Maps for navigation, change songs stored on the system’s hard drive or output real-time information coming from your vehicle.

 Tizen’s website notes that the software will eventually be designed for tablets and netbooks as well as smartphones, but it’s also slated to come to Smart TVs. This isn’t very surprising considering Samsung is a major player in pioneering the Smart TV category.

TIZEN

Tizen is an open source, standards-based software platform supported by leading mobile operators, device manufacturers, and silicon suppliers for multiple device categories such as smartphones, tablets, netbooks, in-vehicle infotainment devices, and smart TVs. Tizen offers an innovative operating system, applications, and a user experience that consumers can take from device to device.

The Tizen project resides within the Linux Foundation and is governed by a Technical Steering Group. The Technical Steering Group is the primary decision-making body for the open source project, with a focus on platform development and delivery, along with the formation of working groups to support device verticals.

The Tizen Association has been formed to guide the industry role of Tizen, including gathering of requirements, identification and facilitation of service models, and overall industry marketing and education.

Tizen provides a robust and flexible environment for application developers, based on HTML5. With HTML5's robust capabilities and cross platform flexibility, it is rapidly becoming the preferred development environment for mobile apps and services. The Tizen SDK and API allow developers to use HTML5 and related web technologies to write applications that run across multiple device segments.

courtesy:www.tizen.org

HOW TO USE AN S PEN

Samsung added even more functionality to its S Pen stylus in the Galaxy Note 3. Here's everything you need to know to get started.

(Credit: Sarah Tew/CNET)

Samsung's latest flagship device is scheduled to arrive in stores this week. The Galaxy Note 3 is bigger and better in nearly all respects. The company added a larger, 5.7-inch display with a higher resolution, a speedy 2.3GHz quad-core Snapdragon 800 processor, and 3GB of RAM, and gave its S Pen stylus even more features, all while making the device slimmer and sleeker than its predecessor.
The S Pen is the primary reason for the success of the Note line of smartphones and tablets. The special stylus brings added functionality to Samsung's devices, allowing users to quickly take onscreen notes, draw pictures, and much more.
Here's how you can get the most out of the Galaxy Note 3's new S Pen:

Air Command

The S Pen is located on the bottom right-hand side of the Galaxy Note 3. Removing the stylus will cause the device to launch the Air Command menu, which can appear on the home screen or inside of an app. The menu gives quick and easy access to various S Pen features, such as Action Memo, Scrapbooker, Screen Write, S Finder, and Pen Window. It can also be enabled by hovering over the screen and clicking the button on the side of the stylus.

(Credit: Sarah Tew/CNET)

Action Memo
Action Memo is the first option on the Air Command menu. This feature allows you to handwrite notes that can be linked to different actions, such as calling a number you wrote down, adding it as a contact, or sending it as a message or e-mail. You can also search the Internet or Google Maps, or even add the action to your Tasks.
The Galaxy Note 3 can automatically recognize what you write to complete these actions, however the feature seems to have a problem reading poor handwriting, which may leave many users frustrated.
In addition to being able to change the Action Memo background and ink color, notes can also be minimized and placed as a thumbnail on your home screen. Saved notes can be found inside of the Action Memo app in the Galaxy Note 3's app drawer.

(Credit: Sarah Tew/CNET)

Scrapbooker
The second feature on the menu, known as Scrapbooker, gives you the ability to draw around a portion of the screen to take a screenshot. After selecting a certain area of the screen and taking a picture, you can add tags, written notes, and different categories for better organization. Images are then saved in the Pinterest-inspired Scrapbook app on your device.
Screen Write
A feature carried over from previous Note models is Screen Write. This feature takes a screenshot of your current page and then you can write notes on top of the image.
Inside of the Screen Write feature you can change the pen size and color by selecting the pen icon in the upper left-hand corner of the screen. To the right you will find the eraser, crop, undo, and redo tools, along with share, cancel, and save.
S Finder
Apple has Spotlight on its Mac computers and iOS devices, and now Samsung has S Finder. This feature, which can also be accessed with a long-press on the Galaxy Note 3's Menu button, allows you to search for anything on your device, including apps, contacts, and even handwritten notes.
Pen Window
Arguably the coolest thing Samsung included in the Galaxy Note 3, besides the S Pen itself, is a new multitasking feature called Pen Window. This feature lets you draw a box on the screen and then choose from eight different apps -- Calculator, Clock, YouTube, Phone, Contacts, ChatOn, Hangouts, and a browser -- to launch inside of it.
Clicking on the side or bottom of a box will let you resize it, while clicking on the white space at the top will let you move it. Other options include expanding the app to full-screen mode, or even minimizing it into a Chat Head-esque floating icon on your home screen.
To open a second box, simply launch the Air Command menu, select the Pen Window feature, draw a box, and choose a new app.

Settings

The S Pen settings, which can be found in the Controls tab, will let you customize your experience even further. From here you can turn off pen detection, change the action that occurs when you remove the S Pen, enable an onscreen pointer when you hover, and more.

(Credit: Screenshot by Dan Graziano/CNET)

S Pen Keeper
A cool but gimmicky feature Samsung added is the Galaxy Note 3's ability to alert you when the S Pen and smartphone are separated. The feature, which oddly enough only works when the screen is off, can be found in the S Pen settings as the "S Pen keeper" option.
When this is enabled you will receive a popup notification, in addition to your phone vibrating and making a sound when leaving the S Pen behind. Be warned, however, it only seemed to work half the time.

Other features

S Note
Another feature that has been recycled from previous Note models is S Note, which lets you draw and write notes over different templates, images, videos, charts, maps, and so on. The S Note feature isn't found on the Air Command menu, but rather inside of the app drawer.

(Credit: Sarah Tew/CNET)

Pen.Up
Samsung created a social-networking app, called Pen.Up, for Galaxy Note owners wanting to share, comment on, and rate the artwork they and others created using the S Pen. The Pen.Up app is available for Galaxy Note owners as a free download in the Google Play store.
Buttons
One of the biggest complaints among Galaxy Note 2 users was that they couldn't use the stylus on the phone's capacitive buttons. Thankfully this is no longer an issue. The new S Pen now works on the Galaxy Note 3's menu and back button.

S PEN EXPLAINED

The SAMSUNG GALAXY Note has a Wacom dual digitizer, a first in a mainstream smartphone. That means is supports both capacitive multi-touch and active pen input from a precise EMR digital pen and a digitizer layer under the screen. Wacom is the world leader in pen based computer technologies and first developed this technology for Tablet PCs for very accurate handwriting level pen use that works with touch displays.

Details:
Almost all other phone styluses are just capacitive and therefore no more accurate than your finger. The Galaxy Note's active pen uses Wacom's EMR patented technology. EMR which stands for Electo-Magnetic Resonance, which requires no internal power to generate a signal on the pen-side that enables the pen coordinates on or above the screen to be detected (the display provides the power rather than the pen). The Note's screen surface incorporates a sensor board that detects the pen's movement. Weak energy is induced in the pen's resonant circuit by a magnetic field generated by the sensor board surface. The pen's resonant circuit then makes use of this energy to return a magnetic signal to the sensor board surface. The digitizer board under the screen detects information on the pen's coordinate position and angle, as well as on its general operating condition including speed and writing pressure, etc. 

With EMR Technology, the sensor unit is installed behind the display screen. Because the sensor does not cover the front of the display, the quality and brightness of the displayed image are not compromised.

Wacom's sensors are high precision and high resolution, which together make it possible to detect even small hand-written letters. The sensor traces the movement of the human hand and reproduces such "human" elements as the feel, force and ambivalence of the pen tip.

The dual capacitive multi-touch and EMR active pen technology is called Wacom Feel It and was developed and honed over 2 years on major ( HP, ...) Tablet PCs. The Galaxy Note is the first use in a smart phone.

S-PEN EXPLAINED

The SAMSUNG GALAXY Note has a Wacom dual digitizer, a first in a mainstream smartphone. That means is supports both capacitive multi-touch and active pen input from a precise EMR digital pen and a digitizer layer under the screen. Wacom is the world leader in pen based computer technologies and first developed this technology for Tablet PCs for very accurate handwriting level pen use that works with touch displays.

Details:
Almost all other phone styluses are just capacitive and therefore no more accurate than your finger. The Galaxy Note's active pen uses Wacom's EMR patented technology. EMR which stands for Electo-Magnetic Resonance, which requires no internal power to generate a signal on the pen-side that enables the pen coordinates on or above the screen to be detected (the display provides the power rather than the pen). The Note's screen surface incorporates a sensor board that detects the pen's movement. Weak energy is induced in the pen's resonant circuit by a magnetic field generated by the sensor board surface. The pen's resonant circuit then makes use of this energy to return a magnetic signal to the sensor board surface. The digitizer board under the screen detects information on the pen's coordinate position and angle, as well as on its general operating condition including speed and writing pressure, etc. 

With EMR Technology, the sensor unit is installed behind the display screen. Because the sensor does not cover the front of the display, the quality and brightness of the displayed image are not compromised.

Wacom's sensors are high precision and high resolution, which together make it possible to detect even small hand-written letters. The sensor traces the movement of the human hand and reproduces such "human" elements as the feel, force and ambivalence of the pen tip.

The dual capacitive multi-touch and EMR active pen technology is called Wacom Feel It and was developed and honed over 2 years on major ( HP, ...) Tablet PCs. The Galaxy Note is the first use in a smart phone.

TOUCH SCREEN TECHNOLOGY

To begin with, not all touch is created equal. There are many different touch technologies available to design engineers.

According to touch industry expert Geoff Walker of Walker Mobile, there are 18 distinctly different touch technologies available. Some rely on visible or infrared light; some use sound waves and some use force sensors. They all have individual combinations of advantages and disadvantages, including size, accuracy, reliability, durability, number of touches sensed and -- of course -- cost.

As it turns out, two of these technologies dominate the market for transparent touch technology applied to display screens in mobile devices. And the two approaches have very distinct differences. One requires moving parts, while the other is solid state. One relies on electrical resistance to sense touches, while the other relies on electrical capacitance. One is analog and the other is digital. (Analog approaches measure a change in the value of a signal, such as the voltage, while digital technologies rely on the binary choice between the presence and absence of a signal.) Their respective advantages and disadvantages present clearly different experiences to end users.

Resistive touch

The traditional touch screen technology is analog resistive. Electrical resistance refers to how easily electricity can pass through a material. These panels work by detecting how much the resistance to current changes when a point is touched.

This process is accomplished by having two separate layers. Typically, the bottom layer is made of glass and the top layer is a plastic film. When you push down on the film, it makes contact with the glass and completes a circuit.

The glass and plastic film are each covered with a grid of electrical conductors. These can be fine metal wires, but more often they are made of a thin film of transparent conductor material. In most cases, this material is indium tin oxide (ITO). The electrodes on the two layers run at right angles to each other: parallel conductors run in one direction on the glass sheet and at right angles to those on the plastic film.

When you press down on the touch screen, contact is made between the grid on the glass and the grid on the film. The voltage of the circuit is measured, and the X and Y coordinates of the touch position is calculated based on the amount of resistance at the point of contact.

This analog voltage is processed by analog-to-digital converters (ADC) to create a digital signal that the device's controller can use as an input signal from the user.

One of the big advantages of resistive touch panels is that they are relatively inexpensive to make. Another is that you can use almost anything to create an input signal: finger tip, fingernail, stylus -- just about anything with a smooth tip. (Sharp tips would damage the film layer.)

This technology has a lot of disadvantages, however. First, the analog system is susceptible to drift, so the user may have to recalibrate the touch panel from time to time. (If you owned a PalmPilot or other PDA, you may remember having to occasionally go through the recalibration process on their PalmPilot.) Next, the ITO material used for the conductors is brittle and not well suited for bending. Over time, repeated use can cause the ITO to crack, which disrupts the flow of electricity and can result in a dead spot on the touch screen.

In addition, there needs to be a gap between the two sensor planes that must be bridged in order to make contact between the two. Just about the only material suitable for this gap is air, but this presents some problems of its own.

First, the gap adds to the combined thickness of the display and touch module. As the consumers demand thinner and thinner devices, a single millimeter can be a big deal.

Another problem has to do with the optical properties of the different layers. If you look at a drinking straw in a glass of water, it will look as though it is slightly bent where it enters the water, even though it is straight. This is because light can bend, or "refract," when it makes the transition from one material to another. If the materials have the same index of refraction, the light won't change its path, but if the index of refraction is different, the light will bend.

The space between the plastic and glass layers of a resistive touch panel is filled with air, and the air has a different index of refraction than the other layers, which makes the light bend as it passes from one layer to another. This can create visible artifacts that can impact the display quality.

The air gap is especially a problem when you view the display under high ambient light conditions, such as outdoors in bright sunlight. The outside light passes through the top layer, then bends when it hits the air gap, and can then reflect between the glass and plastic layers before exiting out the front of the display again. This bouncing light can reduce the image's contrast, making the display look washed out and impossible to see.

But probably the biggest problem with resistive panels in consumers' eyes is that they can sense only one touch at a time. If you touch the panel in two places at once, the combined effect will produce one coordinate for the touch point, and that will be different from either of the two actual points. There are ways to create resistive panels that can sense multiple touches at one time, but these can be expensive and complex, such as creating a matrix of separate contact pads on one of the layers.

Projected capacitance

Fortunately, there's a better way. Many mobile devices now rely on a technology known as "projected capacitance," often referred to in the industry as "p-cap" or "pro-cap." According to various sources, resistive touch has rapidly lost market share to pro-cap and is forecast to continue to decline.

Pro-cap is a solid-state technology, which means that it has no moving parts (unlike the resistive touch technology). Instead of being based on electrical resistance, it relies on electrical capacitance.

When you apply an electrical charge to an object, the charge can build up if there is no place for the electrons to flow. This "holding" of electrons is known as "capacitance." You have probably experienced this effect first-hand. When you walk across a carpet in rubber-soled shoes in the winter time, electrons can build up in your body. If you should then reach for a light switch or some other conductive object that does not have a similar built-up charge, those electrons can flow from your body to the object, producing a spark of electricity.

If you apply a charge to a conductor, and then bring another conductor near it, the second conductor will "steal" some of the charge from the first one, just as the light switch did when your finger approached it. If you know what the charge was to start with, you can tell when the amount of the charge has changed. This is the principle behind pro-cap touch screens.

Early capacitance touch technologies required that you actually touch a conductive layer. This approach left the conductor exposed to wear and damage. Today's projective capacitance technology relies on the fact that an electromagnetic field "projects" above the plane of the conductive sensor layer. You can cover the touch module with a sheet of thin glass, for example, and it will still sense when a conductor comes near.

Pro-cap touch screens use two layers of conductors, separated by an insulator (such as a thin sheet of glass, though other insulating layers can be used). The conductors typically are made of transparent ITO, just as with the resistive designs. The conductor layers never have to bend, however, so its brittle nature is not a problem with pro-cap screens.

The conductors in each layer are separate, so that the capacitance of each one can be measured separately. As with a resistive panel, the conductors run at right angles to each other, so that the device can sense an X and a Y position when touched. The difference is that the separate conductors are scanned in rapid sequence, so that all the possible intersections are measured many times per second.

When you touch the screen with your finger, it steals a little of the charge from each layer of conductors at that point. The electrical charge involved is tiny, which is why you don't feel any shock when you touch the screen, but this little change is enough to be measured. Because each conductor is checked separately, it is possible to identify multiple simultaneous touch points.

Pro-cap technology is not without its challenges. The system of conductors is susceptible to electrical noise from electromagnetic interference (EMI). This can be a problem for display devices such as LCD and OLED panels that rely on an active matrix backplane of transistors to rapidly switch the individual subpixels on and off. The touch screen controller must be able to filter out this background noise and figure out which signals are from actual touch points.

The controller is often asked to make other decisions as well. Comparing results from adjacent coordinates can help determine if the touch is hard or soft, or if it is the result of the palm of the hand resting on the screen and thus should be ignored. Some smartphones rely on the touch screen to signal when the phone is being held next to the user's face, so that the screen can be turned off to save power.

All these tasks require significant processing power, which makes the controller more expensive. In addition, the touch screen only works when you apply a conductor; the ball of your finger works, but not your fingernail. Some pro-cap screens will work even if you're wearing thin surgical gloves, but they won't work if you have thick winter gloves on. (The exception is if the gloves themselves are conductive; you can buy gloves with conductors woven into the fingertips so that they can conduct the charge from the screen to your finger.)

In spite of these shortcomings, pro-cap technology has become the dominant choice for mobile devices. And there are improvements on the way that could make them even better.

Can't be too thin or too light

Consumers have made it clear that they want smartphones and other mobile devices to be as thin and lightweight as possible. As a result, design engineers are always looking for technology improvements that let them remove layers and materials from their products. And touch screens are not immune to such scrutiny.

The traditional structure for adding pro-cap touch to a display is to purchase a separate module. You would start with an LCD panel that is made up of two glass layers that contain the liquid crystal material; the top glass sheet is covered with a polarizing layer.

Above that goes the pro-cap touch module, which is made by coating both sides of a glass sheet with a conductor (typically ITO), which is then patterned to create the electrodes. This glass sheet is then laminated to the polarizer layer of the LCD panel described in the previous paragraph.

Finally, a protective cover glass is placed on top of the touch panel so that the top electrodes are not exposed. This cover can also have decorations (such as logos or icons for fixed controls) and be designed to protect the display from damage.

If you've been counting, you'll realize that it all adds up to four different sheets of glass in the stack -- which means that even today's thin smartphones aren't as thin as some might prefer. If manufacturers could eliminate one of these sheets, they'd reduce the space required for glass and the weight of the glass in the display by 25%. Those are savings worth pursuing.

A method that is gaining momentum is called the "one-glass solution" (OGS); it eliminates one of the layers of glass from the traditional pro-cap stack. The basic idea is to replace the touch module glass by a thin layer of insulating material. In general, there are two ways to achieve this.

One approach to OGS is called "sensor on lens." (In this case, the "lens" refers to the cover glass layer.) You deposit an ITO layer on the back of the cover glass and pattern it to create the electrodes. You add a thin insulator layer to the bottom of that, and then deposit a second ITO layer on the back of that, patterning it to create electrodes running at right angles to the first layer. This module then gets laminated onto a standard LCD panel.

The other approach is called "on-cell" pro-cap. (Here the "cell" refers to the LCD display.) A conductive layer of ITO is deposited directly onto the top layer of glass in the LCD panel, and then patterned into electrodes. A thin insulating layer is applied, and then the second ITO layer is patterned with the second layer of electrodes. Finally, the top polarizing layer is applied on top, and the display is completed by adding the cover glass.

This may not make much difference to the end user, but it can make a huge difference for the companies in the supply chain -- including which companies are actually included.

When the touch technology is deposited on the cover glass using the sensor on lens approach, you end up with a separate touch module that can be sold to the LCD display assemblers. This would mean more revenues for the touch technology manufacturers who would supply these modules.

On the other hand, the on-cell alternative means that the LCD panel manufacturers can add these touch layers onto their own panels. The display assemblers would then just have to purchase a simple cover glass to complete the display. The touch module makers would be cut out of the process.

For now, it appears that the sensor on lens approach has an advantage over on-cell solutions. The on-cell approach means that LCD makers would have to make two separate models of each panel: one with touch and one without. This could add cost to an industry that is already running on razor-thin margins. Also, on-cell touch is limited to the size of the LCD panel; sensor on glass modules can be larger than the LCD panel, providing room for the dedicated touch points that are part of many smartphone designs.

LCD vs. OLED

In case you've been wondering where OLED displays fit into all this: An OLED display stack is somewhat different from an LCD stack. It only requires one substrate (glass) layer as opposed to LCD's two, and the OLED material layer is much thinner than the LCD layer. As a result, the finished display can be half as thick as an LCD panel, saving weight and thickness -- which is important in a smartphone design.

(A number of smartphones today use a form of active-matrix OLED display called Super AMOLED; these include several Samsung devices such as theGalaxy S III and the Motorola Droid Razr M).

As a practical matter, glass is still used as the encapsulating layer, so OLEDs generally have two layers of glass. In addition, not all OLEDs are RGB -- some use white emitters instead to try to reduce the differential aging problem, and add a color filter layer to the stack.

In spite of all this, as far as touch screen technologies are concerned, OLEDs are more like LCDs than they are different: Both have active matrix TFT backplanes, and both tend to have a cover glass layer for protection. So essentially the same stack configurations are available to OLED panels.

What's next for touch

No matter which solution wins out, it is clear that pro-cap technology is the best method for touch screens on mobile devices -- at least for the foreseeable future. Still, there are some changes already showing up in touch screen technology.

For example, some panel makers are creating "in-cell" touch panels, where one of the conductive layers actually shares the same layer as the thin film transistors (TFTs) used to switch the display's sub-pixels on and off. (These transistors are fabricated directly on the semiconductor backplane of the display.) This approach not only reduces the electromagnetic noise in the system, but also uses a single integrated controller for both the display and the touch system. This reduces part counts and can make the display component thinner, lighter, more energy efficient and more reliable.

This approach only makes sense for very high volume products, such as a smartphone from a major vendor that is expected to sell millions of units, because the panel will have to be made specifically for that unique model. The first products using "in-cell" touch technology have already appeared on the market, such as the new Apple iPhone 5, but it looks as though it will take years before this approach will become a widespread solution.