Dear friends, this article explains how an LED TV's display panel produces an image. Most of the commonly used LED TVs on the market are not made with Organic LEDs. The name "LED TV" originates from the fact that it uses LED strips for the backlight, but the actual display panel is an LCD (Liquid Crystal Display) panel. True LED display technologies include Super AMOLED and OLED. In this article, a detailed overview of how an LCD panel works is provided.
The full form of LCD is Liquid Crystal Display. This display technology is used in countless devices worldwide, from monitors and TVs to laptops and mobile phones. However, the full name is often hidden, as this technology is more accurately known as TFT LCD, or Thin Film Transistor Liquid Crystal Display. The "TFT" part is what makes modern LCDs so fast and effective.
To truly understand how an LCD works, we need to explore its internal layers. A typical LCD panel is incredibly thin, yet it contains six distinct functional layers that work together to create the images we see.
The Six Core Layers of an LCD Panel
To understand the working principle, you must know the names and functions of these six key layers. The light travels from the first layer to the last one.
LED Backlight (Light Source)
Vertical Polarizer (Vertical Polarizing Filter)
TFT Substrate (Thin Film Transistor Array)
Liquid Crystal Substrate (Liquid Crystal Layer)
RGB Color Filter
Horizontal Polarizer (Horizontal Polarizing Filter)
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Fig 1: A visual diagram showing the internal layers of a TFT LCD panel and how each component works together to produce an image. |
A Layer-by-Layer Breakdown: How an LCD Works
Let's now patiently try to understand the function of each layer and see how a picture is formed.
The Backlight: The Light Source
The Backlight is the sole light source for the entire display. The images you see on an LCD screen are not self-illuminated; they are created by blocking or allowing light from the backlight to pass through.
In modern technology, this light source consists of LED backlights, either placed at the bottom of the screen or along the edges of a light-guiding glass. Older displays, however, used high-voltage fluorescent tubes. We can think of the backlight as the engine of the LCD, constantly providing light for the other layers to work with.
The Vertical Polarizer: A Light Gatekeeper
What is a polarizer? A polarizer is a special film, typically made of PVA (Polyvinyl Alcohol), that acts as a filter for light waves. Light from the backlight is "unpolarized," meaning its waves are vibrating in all directions.
The vertical polarizer is the first layer of the LCD panel. Its job is to filter the unpolarized light, allowing only the light waves that are oscillating in a vertical direction to pass through. It blocks all other light waves, ensuring that the light reaching the next layer is perfectly polarized.
The TFT Substrate: The Pixel Switches
TFT stands for Thin-Film Transistor. An LCD screen is made up of millions of tiny pixels. Each pixel is individually controlled by a small transistor- the TFT.
The TFT substrate is a glass layer covered with a thin film of semiconductor material (amorphous silicon), where these tiny transistors are arranged in a grid. Each TFT acts as a high-speed switch that controls the precise voltage supplied to its corresponding pixel's liquid crystal cell. The primary function of the TFTs is to ensure that each pixel can be turned on or off with incredible speed and accuracy, which is essential for displaying high-quality images and video.
Understanding Driver Voltages (AVDD, VGH, VGL, VCOM)
For the TFTs to work, they need specific voltages, which are supplied by driver integrated circuits (ICs).
VGH (Gate High): This is a high positive voltage that is sent to the gate of the TFT to turn it ON.
VGL (Gate Low): This is a low negative voltage that is sent to the gate of the TFT to turn it OFF.
AVDD (Analog VDD): AVDD is the main positive voltage supply for the source of the TFT.
VCOM (Common Voltage): This is the voltage applied to the common electrode on the other side of the liquid crystal layer. It acts as a reference voltage.
By carefully controlling these voltages, the driver ICs can rapidly switch each pixel on and off, allowing for precise image control.
The Liquid Crystal Layer: The Light Twisters
The liquid crystal layer is a fascinating material that plays a crucial role in light manipulation. These crystals are unique because their molecules can change their orientation when an electric current is applied.
When a voltage is applied by a TFT, the liquid crystals twist. The degree of twisting depends on the voltage level. This twisting action changes the polarization of the light that is passing through them. Essentially, the liquid crystals act as shutters, controlling how much light can pass through each pixel.
The Color Filter: The Color Creator
The color filter is what gives an LCD its color. It is a layer placed over the pixels, which are each divided into three tiny sub-pixels: Red, Green, and Blue (RGB).
The color filter's job is to selectively filter the white light coming from the backlight. As the light passes through a specific sub-pixel, the filter allows only its corresponding color wavelength (red, green, or blue) to pass through. By precisely controlling the brightness of each of these three sub-pixels, the display can create a full spectrum of colors.
The Horizontal Polarizer: The Final Filter
The horizontal polarizer is the final layer before the viewer's eye. It is oriented horizontally and allows only light waves that are vibrating horizontally to pass through.
The light has now passed through two polarizers and the liquid crystal layer. When no voltage is applied to a pixel, the liquid crystals naturally twist the light, allowing it to pass through the horizontal polarizer. When a voltage is applied, the crystals untwist, blocking the light. This selectively blocking or allowing light to pass through is how the LCD creates the images you see on the screen.
Video Explanation
To better understand this fascinating process, you can watch the video below, which explains how an LCD works in a practical way.
1 comment:
very nice!!!!!
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