Explaining LCDs, Touchscreen Panels and Touchscreen Digitizers

Digital display technology has come a long way since its inception. Today, we’re surrounded by screens – from the ubiquitous smartphones and tablets to laptops and information kiosks. All these devices rely on a variety of display technologies, primarily LCD (Liquid Crystal Display), touchscreen panels, and digitizers. This article aims to elucidate the mechanics behind these intricate technologies and illustrate how they cohesively function to provide the end-user with a seamless experience.

What is LCD?

LCD is the acronym for Liquid Crystal Display, the commonly used technology for displays in notebooks, other automated industry computers, and an array of mobile devices. LCD technology is favored over Cathode Ray Tube (CRT), Light Emitting Diode (LED), and gas-plasma technologies for its slimness and power-efficiency. It primarily operates on the principle of blocking light as opposed to emitting it.

Modern LCD displays typically utilize active-matrix technology, which contains Thin Film Transistors (TFTs). These transistors incorporate capacitors enabling individual pixels to actively retain their charge, making these displays more efficient and responsive. When the backlight provides an even light source behind the LCD screen, this polarized light shines through to the liquid crystal layer. Here, the crystals, which can be twisted by applying an electrical voltage, either block the polarized light or reflect colored light (red, green, or blue) when activated.

Touch Screen Panels

Touchscreen panels are devices that sense physical touch, either by a person’s hands or a stylus, and perform actions based on the touch’s location and the number of touches. Serving as a viable alternative to a mouse or keyboard, touchscreens are used on various devices, including computer and laptop displays, smartphones, tablets, cash registers, and information kiosks.

Touchscreens work through one of four basic systems: Resistive, Capacitive, Infrared, and Surface Acoustic Wave. Each of these systems uses different techniques to recognize touch and translate it into commands that the device can interpret and respond to.

Touch Screen Digitizers

A touch screen digitizer is essentially a transparent sheet layered on top of the screen in a multilayered sandwich-like arrangement. It is equipped with a grid of microscopically small sensors. When the screen is touched, these sensors immediately trigger, sending signals to an electronic circuit. This circuit converts the signals into specific X and Y coordinates, which are then passed to the software. Depending on the application being used, the software interprets the touch and location.

Different Types of Digitizers

There are mainly two types of touchscreen digitizers: Resistive and Capacitive.

  1. Resistive Touchscreen Digitizer: This type of digitizer consists of several layers, including two thin conductive layers separated by a thin space. When you press down on the touchscreen’s outer layer, it makes contact with the inner layer, and the touch is registered, causing changes in electrical current and registering the command. This technology can recognize input from various touch sources, including fingers, styluses, and gloves, but it lacks multitouch capabilities and has lower clarity compared to capacitive screens.
  2. Capacitive Touchscreen Digitizer: Unlike resistive touchscreens, capacitive touchscreens are made of a single layer coated with a transparent conductor. When a small amount of electrical charge (applied by a human touch) disrupts the screen’s electrostatic field, the device registers the touch. Capacitive touchscreens are generally more responsive and offer multitouch capabilities, enabling pinch-to-zoom and other complex gestures. They can only be used with bare fingers or specialized devices like capacitive styluses because they rely on the conductivity of the human body to operate.
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How Does a Touchscreen Digitizer Work?

The operation of a digitizer begins with the detection of a touch event. When you touch the screen with your finger or a stylus, the digitizer detects the touch point. For resistive screens, this happens when the two layers make contact at the point of touch, while for capacitive screens, the disruption in the electrostatic field marks the event.

The digitizer then calculates the coordinates of the touch event. It translates these analog signals (changes in electrical current for resistive, electrostatic disruption for capacitive) into digital signals that the device’s processor can understand.

These signals are sent to the device’s operating system, which interprets them as specific commands or actions. For instance, if you tap an app icon on your smartphone screen, the operating system interprets this as a command to open the app.

digitizer

The touchscreen display and the digitizer work together to provide an interactive experience, but they are not the same. The display presents the visual output that the users see, while the digitizer detects and processes touch input.

Do All Touchscreen Devices Have a Digitizer?

Yes, all touchscreen devices include a digitizer. It is the essential component that allows a device to interpret touch inputs. However, not all digitizers are created equal. There are different types of touchscreen technologies, each with its own method of detecting touch, including resistive, capacitive, infrared, and surface acoustic wave (SAW) technologies, among others.

In a resistive touchscreen, which is less common in modern consumer electronics but still widely used in certain industrial applications, the digitizer works by responding to pressure. This screen consists of two flexible layers separated by a small gap. When you press down on the screen, these layers touch, and the device translates the precise location of that touch into a command.

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Capacitive touchscreens, the most common type found in modern smartphones, tablets, and touch-enabled laptops, use the electrical conductance of the human body to detect touch. They consist of a glass panel coated with a transparent conductor. When a human finger, which is also an electrical conductor, touches the screen, it results in a change in the screen’s electrostatic field and registers the touch.

So, regardless of the technology used, a digitizer is a crucial part of any device’s touchscreen functionality. It’s the component that translates your touch inputs into commands that the device can interpret and respond to.

The Bottom Layer: Touch Screen Glass

The bottom layer in the touchscreen panel is the ITO (Indium Tin Oxide) glass, usually with a thickness between 1 and 3 millimeters. It forms the basis for a touch screen panel and can be customized according to customer needs. When this glass cracks due to, say, a fall, it results in a characteristic spider-web-like pattern.

The Integrated Display: A Cohesive Interaction of Components

The glass forms the bottom layer of the touchscreen, which can be customized to customer needs. The digitizer, fused with the glass screen, senses and responds to touch, acting as a data input for the device’s processing center. It is an integral part of the touch screen panel, which is the thin, transparent layer of plastic that reads the signal from the touch and transports it to the processing unit.

When the glass or the digitizer needs to be replaced, the entire assembly (glass and digitizer) typically has to be replaced due to their fused nature. The LCD, the visual component underneath the glass, displays the image on the screen. Accessing the LCD for any repairs or replacement involves disassembling the device.

An essential element of touchscreens is a digitizer, a component often misunderstood or overlooked entirely by consumers. This article aims to delve into the world of touchscreen digitizers, explaining what they are and how they work.

Marcus Richardson
Editor-in-chief

I love testing and writing about new tech. I'm also a gamer and an engineer. Check out my Twitter for keyboard stuff.

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