17.2 Flat panel display technologies (LCD, OLED, etc.)
5 min read•august 7, 2024
Flat panel displays have revolutionized how we interact with visual information. From smartphones to TVs, these technologies shape our daily lives. and are the two main types, each with unique strengths in image quality and energy efficiency.
This section dives into the inner workings of LCDs and OLEDs, exploring their components and driving mechanisms. We'll also look at newer technologies like and examine key performance metrics that determine display quality.
LCD and OLED Display Technologies
Liquid Crystal and Organic LED Displays
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- Liquid Crystal Display (LCD) uses to modulate light and create images
- Liquid crystals are substances that exhibit properties between those of conventional liquids and solid crystals
- LCDs require a to illuminate the display since liquid crystals do not emit light themselves
- Common types of LCDs include Twisted Nematic (TN), In-Plane Switching (IPS), and Vertical Alignment (VA)
- Organic Light-Emitting Diode (OLED) displays use that emit light when an electric current is applied
- OLEDs are self-emissive and do not require a backlight, resulting in thinner displays and better power efficiency
- Each pixel in an OLED display can be individually controlled, allowing for deeper blacks and higher contrast ratios compared to LCDs
- OLED displays are used in smartphones ( Galaxy series), televisions ( OLED TVs), and other devices
Quantum Dot and Backlight Technologies
- Quantum dot displays enhance the and of LCDs by using semiconductor nanocrystals
- Quantum dots are placed between the backlight and the LCD panel to convert light into more saturated colors
- They enable a wider color gamut, allowing for more vivid and accurate color reproduction
- Quantum dot displays are used in high-end televisions (Samsung QLED TVs) and monitors
- Backlight technologies provide illumination for LCD displays
- (CCFLs) were commonly used in the past but have been largely replaced by
- LED backlights offer better power efficiency, longer lifespans, and thinner display designs compared to CCFLs
- Local dimming LED backlights can selectively dim or turn off LEDs in specific areas to improve contrast and black levels
Color Gamut and Display Performance
- Color gamut refers to the range of colors a display can reproduce
- A wider color gamut allows for more vibrant and accurate colors
- Common color gamut standards include , , and
- High-end displays often support a wider color gamut, such as DCI-P3, which is used in the film industry
- Display performance is influenced by various factors, including , brightness, and
- Color accuracy ensures that the displayed colors match the intended colors as closely as possible
- Brightness, measured in nits or candelas per square meter (cd/m²), determines how well a display performs in well-lit environments
- Contrast ratio is the difference between the brightest white and the darkest black a display can produce, with higher ratios resulting in more detailed images
Display Driving Schemes
Thin-Film Transistor (TFT) Technology
- () is a type of field-effect transistor used to control pixels in LCD and OLED displays
- TFTs are fabricated on a thin film of semiconductor material, typically amorphous silicon or polycrystalline silicon
- Each pixel in a TFT display has its own transistor, allowing for precise control over the pixel's brightness and color
- TFT technology enables the creation of high-resolution displays with fast response times and good color reproduction
- TFT displays are commonly used in laptops, computer monitors, and televisions
- TFT LCDs have largely replaced older displays due to their superior image quality and performance
- TFT OLEDs offer even better image quality and power efficiency compared to TFT LCDs
Active and Passive Matrix Driving Schemes
- is a display driving scheme that uses a TFT for each pixel, allowing for individual pixel control
- In an active matrix display, each pixel is independently addressed and controlled by its own TFT
- Active matrix displays offer faster response times, higher contrast ratios, and better viewing angles compared to passive matrix displays
- Examples of active matrix displays include TFT LCDs and Active-Matrix OLEDs (AMOLEDs)
- Passive matrix is an older display driving scheme that uses a grid of conductive traces to control pixels
- In a passive matrix display, pixels are addressed by row and column, with each pixel at the intersection of a row and column trace
- Passive matrix displays are simpler and cheaper to manufacture than active matrix displays but suffer from slower response times and lower image quality
- Examples of passive matrix displays include STN () LCDs and Passive-Matrix OLEDs (PMOLEDs)
Display Performance Metrics
Refresh Rate and Response Time
- is the number of times per second a display updates its image, measured in Hertz (Hz)
- Higher refresh rates result in smoother motion and reduced motion blur
- Common refresh rates include 60Hz, 120Hz, and 144Hz
- High refresh rate displays (120Hz and above) are popular for gaming and fast-paced content
- is the time it takes for a pixel to change from one color to another, typically measured in milliseconds (ms)
- Faster response times reduce ghosting and motion blur, resulting in clearer images during fast-moving scenes
- TN panels generally have the fastest response times (1-5ms), while IPS and VA panels have slower response times (5-20ms)
- OLED displays have very fast response times (< 1ms) due to their self-emissive nature
Viewing Angle and Contrast Ratio
- is the maximum angle at which a display can be viewed without significant degradation in image quality
- Wider viewing angles allow for more flexibility in display placement and viewing position
- IPS and OLED displays generally have wider viewing angles (178° or more) compared to TN displays (160° or less)
- Displays with narrow viewing angles may exhibit color shifts or brightness changes when viewed from off-center positions
- Contrast ratio is the ratio of the luminance of the brightest white to the darkest black a display can produce
- Higher contrast ratios result in deeper blacks, brighter whites, and more detailed images
- Static contrast ratio measures the contrast between the brightest and darkest pixels simultaneously displayable
- Dynamic contrast ratio measures the contrast between the brightest and darkest pixels the display can produce over time (e.g., by adjusting backlight brightness)
- OLED displays have the highest contrast ratios (1,000,000:1 or more) due to their ability to completely turn off individual pixels for perfect blacks
Key Terms to Review (29)
Active matrix: An active matrix is a technology used in flat panel displays that employs a grid of transistors to control individual pixels, allowing for faster refresh rates and improved image quality. This technology is crucial in liquid crystal displays (LCDs) and organic light-emitting diode (OLED) screens, as it enables each pixel to be turned on or off independently, resulting in more vibrant colors and sharper images.
Adobe RGB: Adobe RGB is a color space developed by Adobe Systems that encompasses a broader range of colors compared to the standard sRGB color space, particularly in the green and cyan regions. This wider gamut allows for more vibrant and accurate color representation, making it particularly useful for professional photography and graphic design applications, where precise color management is critical.
AMOLED: AMOLED, or Active Matrix Organic Light Emitting Diode, is a display technology that combines organic compounds to emit light when an electric current is applied, allowing for vivid colors and deep blacks. This technology enables each pixel to emit its own light, resulting in better contrast and energy efficiency compared to traditional LCDs, making it popular in smartphones and high-end televisions.
Backlight: A backlight is a source of artificial light used in flat panel displays, primarily to illuminate the screen and enhance visibility. It plays a crucial role in technologies like LCDs, where it provides brightness and contrast, and is essential for the overall viewing experience. The type of backlighting used can significantly affect color accuracy, power consumption, and display thickness.
Brightness: Brightness refers to the perception of how much light is emitted or reflected from a surface, impacting visibility and clarity. It plays a critical role in display technologies, influencing color reproduction and overall viewing experience, while also being significant in projection systems for clarity and detail. In single-photon sources and detectors, brightness indicates the rate at which photons are emitted or detected, affecting sensitivity and performance in various applications.
Cold Cathode Fluorescent Lamps: Cold cathode fluorescent lamps (CCFLs) are a type of lighting technology that uses a gas-filled tube to produce light, operating at low pressure and utilizing cold cathodes to emit electrons. This technology is widely recognized for its application in backlighting for flat panel displays, providing an efficient and uniform light source that enhances image quality and color reproduction.
Color accuracy: Color accuracy refers to the degree to which a display reproduces colors that match the original source accurately. This is crucial for applications like photo editing and graphic design, where precise color representation is vital. A display with high color accuracy ensures that what you see on screen closely resembles real-world colors, making it important for creative professionals and anyone who values true-to-life visuals.
Color gamut: Color gamut refers to the complete range of colors that a device can reproduce or display. This concept is crucial for understanding how different technologies, such as displays and projectors, handle color reproduction and representation. A broader color gamut indicates a device's ability to produce more vivid and varied colors, impacting the overall quality and accuracy of images and videos.
Contrast Ratio: Contrast ratio is a measurement that compares the luminance of the brightest white to the darkest black that a display or projection system can produce. A higher contrast ratio indicates a greater difference between light and dark, which results in better image quality and depth perception. This metric is crucial for assessing display performance, as it impacts color accuracy, detail visibility, and overall viewing experience.
DCI-P3: DCI-P3 is a color space commonly used in digital cinema that encompasses a wider range of colors than the traditional sRGB color space. It was developed by the Digital Cinema Initiatives to provide filmmakers with more vibrant and accurate color representation for film and video content. DCI-P3's broader gamut allows for richer color reproduction, which is essential in flat panel display technologies, enhancing the visual experience in applications like cinema, television, and high-end monitors.
LCD: LCD, or Liquid Crystal Display, is a flat panel display technology that uses liquid crystals to modulate light and create images. This technology is widely utilized in screens for televisions, computer monitors, and smartphones due to its thin profile and energy efficiency. LCDs work by controlling the amount of light that passes through liquid crystals, allowing for a range of colors and images to be displayed.
LED Backlights: LED backlights are a type of lighting technology used in flat panel displays, where light-emitting diodes (LEDs) illuminate the screen from behind or along the edges. This method enhances image quality by providing brighter and more vibrant colors, while also improving energy efficiency compared to traditional backlighting methods. The integration of LED backlights has become a key feature in both LCD and OLED technologies, allowing for thinner displays and better contrast ratios.
Lg: The term 'lg' stands for the logarithm base 10, also known as the common logarithm. It is a mathematical function that is used to express how many times a number, called the base, must be multiplied by itself to yield a given value. In the context of flat panel display technologies, lg plays an essential role in understanding brightness levels, contrast ratios, and image quality metrics that are crucial for evaluating display performance.
Liquid crystals: Liquid crystals are a state of matter that has properties between those of conventional liquids and solid crystals. They flow like a liquid but have some degree of order, which is crucial in the functioning of flat panel displays by allowing control over light passage when manipulated by electric fields.
OLED: OLED, or Organic Light Emitting Diode, is a display technology that uses organic compounds to emit light when an electric current is applied. Unlike traditional displays, OLED screens do not require a backlight, allowing for thinner panels and superior contrast ratios. This technology is crucial in modern flat panel displays, enhancing color accuracy and energy efficiency.
Organic compounds: Organic compounds are chemical substances that primarily consist of carbon atoms, often in combination with hydrogen, oxygen, nitrogen, and other elements. They are essential to various technologies, including those found in modern display systems, where organic materials play a crucial role in the functionality and performance of devices.
Passive Matrix: A passive matrix is a type of display technology where each pixel in the screen is controlled by a grid of intersecting conductors. This approach allows for simpler circuitry and cost-effective manufacturing but results in slower refresh rates and lower image quality compared to active matrix displays. Passive matrix technology is commonly used in older liquid crystal displays (LCDs) and certain OLED screens.
PMOLED: PMOLED, or Passive Matrix Organic Light Emitting Diode, is a type of display technology that uses organic compounds to emit light in response to electrical currents, relying on a passive matrix addressing scheme. This technology is characterized by its simpler construction and lower cost compared to more complex display types, making it suitable for smaller displays and less demanding applications.
Quantum Dots: Quantum dots are nanoscale semiconductor particles that have unique optical and electronic properties due to quantum mechanics. These tiny particles can emit light of specific wavelengths when excited, making them valuable in various applications including displays, solar cells, and biological imaging.
Refresh rate: Refresh rate refers to the number of times a display updates its image per second, measured in hertz (Hz). A higher refresh rate means smoother motion and less blurring in fast-moving images, which is crucial for an optimal viewing experience in modern flat panel display technologies. This feature significantly impacts the performance of displays like LCDs and OLEDs, especially when rendering video games, movies, or high-speed sports.
Response Time: Response time refers to the duration it takes for a device to react to a change in input or stimulus, particularly in optoelectronic devices. This concept is crucial for assessing the performance and efficiency of components like photodetectors, photodiodes, and modulators, as it directly affects their operational speed and suitability for various applications.
Samsung: Samsung is a South Korean multinational conglomerate known for its wide range of electronics and technology products, including smartphones, televisions, and home appliances. In the context of flat panel display technologies, Samsung has made significant contributions through its development and production of both LCD and OLED screens, leading to innovations that have shaped the market.
Semiconductors: Semiconductors are materials that have electrical conductivity between that of a conductor and an insulator, making them essential for modern electronic devices. Their unique properties enable them to control electrical current, which is fundamental for optoelectronic applications like lasers, LEDs, and photodetectors. They can be manipulated through doping, allowing for tailored electronic behavior and enhanced functionality in various applications.
Sony: Sony is a multinational conglomerate known for its diverse range of electronics, gaming, and entertainment products. In the context of flat panel display technologies, Sony has made significant contributions to the development and commercialization of LCD and OLED technologies, which have become integral to modern televisions and monitors.
SRGB: sRGB stands for standard Red Green Blue, which is a color space that was created to provide a consistent way to represent colors across different devices, such as monitors, printers, and cameras. It defines a specific range of colors that can be displayed, ensuring that images appear similar regardless of where they are viewed. This consistency is crucial in flat panel display technologies where accurate color reproduction directly impacts user experience and visual quality.
Super Twisted Nematic: Super twisted nematic (STN) is a type of liquid crystal display technology that employs a twisted structure of liquid crystals to enhance contrast and response time, making it ideal for various flat panel displays. The 'super twisted' configuration refers to a higher degree of twist in the liquid crystal layers compared to standard twisted nematic displays, which allows for better light modulation and viewing angles. This feature significantly improves the performance of the display, especially in applications requiring wide viewing angles and vibrant colors.
TFT: TFT, or Thin-Film Transistor, is a type of field-effect transistor used in display technology to improve image quality and control over pixel activation in flat panel displays. By using an individual transistor for each pixel, TFT technology allows for better color reproduction, faster refresh rates, and enhanced viewing angles, making it a crucial component in modern LCD and OLED displays.
Thin-Film Transistor: A thin-film transistor (TFT) is a type of field-effect transistor that is made by depositing a thin layer of semiconductor material onto a substrate. This technology is crucial for driving pixels in flat panel displays, allowing for better image quality and efficiency in technologies like LCD and OLED displays.
Viewing Angle: Viewing angle is the measure of the maximum angle at which a display can be viewed while still maintaining acceptable image quality. A wider viewing angle allows users to see the screen from different positions without experiencing significant color distortion or loss of brightness, making it an important factor in the performance and usability of flat panel display technologies.