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📦 TFT LCM (LCD Module) Structure:
LCM is mainly composed of 5 units:
- ✨ BLU（Backlight Unit)
- ✨ POL (Polarizer)
- ✨ LCD (Liquid Crystal Display) Panel
- ✨ IC（Integrated Circuit)
- ✨ FPC (Flexible Printed Circuit)
The below figure is the structure diagram of the TFT-LCD Module. We will briefly introduce the main functions of each on display.
🔆 BLU（Backlight Unit）
The backlight unit is one of the key components of the LCD. It consists of multiple layers of optical sheets and the light source. The role of the backlight unit is to supply sufficient brightness and evenly distribute the light source to the LCD panel given the liquid crystal molecules cannot emit light themselves. Normally, the light source is the LED strips, so it is also called LED-Backlit. The quality of the backlight determines some important features of the display, such as the brightness, uniformity of the outgoing light, and color level of the LCD screen. In general, the BLU largely determines the luminous effect of the LCD screen.
🌀 POL (Polarizer)
A polarizer is to convert natural light without polarization into polarized light and control which light patterns can pass through the LCD panel. Without these filters, visual images generated by the LCD panel have poor performance in contrast ratio.
🧠 IC (Integrated Circuit)
An integrated circuit (IC) is a chip device that consists of a set of integrated circuits. It is used to adjust and control the phase, peak value, frequency, and other parameters of Potentiometric signals on the transparent electrode, to establish the driving electric field, and finally realize the information displayed on the screen.
📎 FPC (Flexible Printed Circuit Board)
FPC is the abbreviation of a flexible printed circuit board. By connecting the LCD panel, FPC can realize the working principle of the circuit, and output the interface that the motherboard needs to match, so that the LCD can work from an electrical point of view.
🧊 LCD (Liquid crystal display) panel / Cell layer
The cell layer is a packaging of liquid crystals embedded between two glass substrates, a top glass substrate with the color filter (CF) and a down glass substrate with the Thin Film Transistor array (TFT-Array). It is also called the LCD panel and is an essential unit of the color display. On the TFT substrate, it can control the pixel voltage on this side precisely. And it is the pixel voltage applied to the liquid crystal that controls the twist of the liquid crystal. On the CF substrate, a pixel is divided into three sub-pixels: red (R), green (G), and blue (B). The liquid crystal (LC) that acts as a light valve adjusts the amount of light of the three primary colors of RGB passing through the CF substrate, and the desired color display can be obtained. To create an image, all the above layers should collaborate like an orchestra.
🔬 Working of the LCD
LCD is a product of optoelectronics. We can get a general understanding of how LCD works from both optical and electrical perspectives.
🔍 Optoelectronic working principle of the LCD
Optical perspective
- Light can be divided into different polarization directions.
- Lights with different polarization directions pass through the liquid crystal, and there will be different optical paths.
- After the light is recombined through this optical path difference, it will change the form of its polarization.
- With the polarizer blocking the light in a certain polarization direction, the transmittance of the light can be determined.
Electrical perspective
- Under different voltages, the liquid crystal will have different arrangements.
- Different liquid crystal arrangements cause different optical path differences, thus making the transmittance change.
- So that the video signal (electricity) can be converted into a bright and dark display (light).
⚙️ Working Process of the LCD
The liquid crystal used in TFT-LCD is TN (Twist Nematic) type liquid crystal. Molecules line up parallelly along grooves and rotate 90° between two surfaces with perpendicular grooves.
🔅 Working of Polarizer
The polarizer filters general light into polarized light. It allows light through when aligned with the polarizer axis and blocks it when perpendicular.
🔁 Optical Effects in Full LCD Layer
When the upper and lower polarizers are perpendicular:
- Without voltage: light rotates and passes through
- With voltage: light cannot rotate, is blocked
🎨 Creating Images through TFT-LCD
Scan driver IC and data driver IC control pixel states. ON = no light, OFF = allows light through CF, forming RGB light synthesis.
how does LCD work to create a color image
