1、 LVDS interface: the "evergreen tree" in the industrial field

Since its birth in the 1990s, LVDS (Low Voltage Differential Signaling) interface has remained an irreplaceable core standard for medium and large-sized industrial LCD screens due to its excellent anti-interference performance, low power consumption, and extremely high industry chain maturity.

1. Working principle of physical layer: Why do differential signals have super strong anti-interference ability?

Ordinary TTL/CMOS signals use single ended signal transmission and are extremely sensitive to ground level changes. They are easily affected by common mode noise interference in industrial environments such as high voltage, high-power motors, solenoid valves, etc. And LVDS has completely introduced differential signaling technology:

• Working mechanism：LVDS relies on a pair of twisted pair cables (positive and negative signal lines) to transmit one signal. By changing the current direction of the 3.5 mA constant current source at the transmitting end, a weak swing bias voltage of 350 mV is generated on the matching resistor at the 100 Ω terminal of the receiving end (usually the common mode voltage V_cm is about 1.2V).
• Anti common mode interference：Due to the two wires being twisted together, electromagnetic interference generated by the external environment will be loaded onto both wires in the same direction simultaneously. The differential amplifier at the receiving end only calculates the voltage difference (V+- V -) between the positive and negative lines, and external common mode interference is automatically hedged and perfectly cancelled out during subtraction.

2. LVDS Channel Configuration Decryption: Differences between Single/Dual Channels and 6-Bit/8-Bit

In the specifications of LCD panels, we often come across channel descriptions such as "Single Link" or "Dual Link", whose physical essence is as follows:

• Data Lanes Allocation：Each set of differential symmetry is a Lane. A complete LVDS transmission channel consists of a set of clock pairs (CLK+/-) and several sets of data pairs (D+/-).
    -6-Bit panel (supporting 262000 colors): requires 1 set of clock channels and 3 sets of data channels (D0, D1, D2), totaling 4 pairs of physical differential wiring.
    -8-Bit panel (supporting 16.7 million colors, mainstream industrial control): requires 1 set of clock channels and 4 sets of data channels (D0, D1, D2, D3), a total of 5 pairs of physical differential wiring.
• Single Link vs Dual Link:
    -Single channel: Only one pixel is transmitted per clock cycle. Due to the bandwidth bottleneck of a single channel, it generally only supports up to 1366 x 768 @ 60Hz image output.
    -Dual channel: Split the image signal into odd pixel channel (Odd) and even pixel channel (Even) for parallel output, equivalent to doubling the bandwidth. It can easily support up to 1920 x 1200 @ 60Hz specifications.

3. Typical LVDS 30 Pin (FIX-30) Pin Physical Definition

Industrial grade 15 inch, 17 inch, and 19 inch LCD screens (especially square screens) most commonly use the standard FIX-30 Pin physical interface form. Here is a table of the most standard pin definitions and layouts for you:

2、 EDP interface: a pioneer in high-resolution and modern microarchitecture

EDP (Embedded Display Port) is an embedded internal display interface standard derived from the VESA Video Association's Display Port protocol. Due to the comprehensive integration of video sources by modern processors such as Intel, AMD, Qualcomm, NXP, etc., eDP is rapidly replacing traditional LVDS interfaces and leading industrial displays and medical high-resolution screens towards the next generation.

1. The Three Core Signal Components of eDP Interface

Unlike the redundant design of LVDS, which requires bundling a physical high-frequency clock line for each channel, eDP directly integrates high-frequency pixel clock signals into the data stream (using 8b/10b encoding), greatly reducing routing at the physical layer. A standard eDP connection channel is constructed from only three physical components:

• Main Link：Specially designed for ultra high speed image packet transmission. Usually, 1-Lane, 2-Lane, or 4-Lane physical links are provided. Because it eliminates the need for independent clock physical lines, the cable layout is simplified and more electrically stable.
• AUX CH - Auxiliary Channel：A highly creative half duplex bidirectional differential auxiliary channel with a transmission bandwidth of 1 Mbps. It is not responsible for transmitting the pixels themselves, but is used for low latency communication between the main control board and the display screen: to read real-time EDID parameters of the screen (color space, resolution, refresh rate timing, etc.), control LCD backlight adjustment, and link quality adaptive detection (Link Training).
• HPD - Hot Plug Detect：Single digital input signal line. After the screen is powered on and initialized, the LCD board's onboard controller will raise the level of this pin, informing the industrial motherboard in real time that it can transmit videos through the AUX channel and enable the main video link at any time.

2. The four core technological advantages of eDP interface

• Extraordinary transmission bandwidth and high-resolution driving capability：Under the eDP 1.4a protocol specification, a single channel (1-Lane) transmission rate can reach 5.4 Gbps (HBR2). Only 2 sets of differential pairs are needed to support 1920 x 1080 @ 60Hz ultra clear images; 4-Lane can easily drive 4K (3840 x 2160) and even higher order high refresh rate, HDR industrial images.
• Significant reduction and miniaturization design of cables：To transmit the same 1080P resolution, the LVDS interface requires at least 20-30 complex cable combinations, including dual channels, while eDP only requires around 10-20 cables, greatly simplifying the internal wiring of the device.
• High integration of backlight control：The eDP protocol not only includes data signals, but its industrial connectors also directly encapsulate the logic power supply of the LCD, LED backlight drive power input, backlight enable (EN), and high-sensitivity PWM dimming signals into 30 pin or 40 pin micro coaxial cables. Truly achieving 'one line running through the full screen'.
• Lower overall power consumption of the system：Thanks to the streamlined physical pins and support for PSR (Panel Self Refresh) low-power features, the system can even turn off the GPU output link when the screen is still, relying solely on the screen's own T-CON refresh, greatly reducing device energy consumption and overall heat generation.

3、 Deep benchmarking of LVDS and eDP core parameters

To assist R&D engineers and procurement decision-makers in establishing quantitative comparisons, we conducted in-depth benchmarking of the main parameters of physical and system characteristics

4、 Selection pain points and application guidelines in industrial application scenarios

The selection of industrial control display products is not based on the core goal of "highest indicators", but more on "high system stability, extremely long stocking life cycle, and comprehensive holding cost". Here is a detailed analysis of common selection pain points for you:

1. Pain point one: How can classic old industrial motherboards adapt to the new generation of high-resolution IPS screens?
• Situation analysis：Many industrial instruments, medical display terminals, or classic entertainment game consoles have industrial control motherboards with a lifespan of over ten years, and most of these classic motherboards are originally only equipped with traditional 30 Pin LVDS interfaces. But currently, the new generation of IPS LCD panels on the market, which have extremely bright colors, ultra wide temperature characteristics, and a 178 ° full view angle (such as Sharp's classic industrial high-resolution screen), have already been forced to switch to eDP signal specifications at the factory in order to pursue ultra-thin and high image quality. There is an absolute protocol generation gap between the host and the screen.
• The Perfect Solution：No need to spend huge reset costs to replace the motherboard. You only need to install a professional "LVDS to eDP active signal transfer bridge board" (usually equipped with industrial grade high-sensitivity chips such as RTD2168 or Longxun LT8918) between the LVDS signal line and the LCD panel. The adapter board reconstructs and modulates the LVDS physical data output from the motherboard and the external backlight dimming signal into a data stream that complies with eDP specifications, completely achieving seamless compatibility with modern high-resolution screens for old hosts.

2. Pain point 2: How to choose the most reliable and reliable wiring scheme under complex and harsh working conditions?
• Key points of LVDS wiring：Industrial control equipment is often accompanied by continuous vibration or surrounding high-power high-voltage lines and heat sources. LVDS cables must first be paired with twisted pair cables wrapped in high-density metal braided shielding mesh, and equipped with terminal housings with physical and mechanical anti stripping self-locking buckles (such as the classic FIX-30, DF14, DF19 series ultra-thin connectors from industrial control) to prevent screen flickering caused by long-term vibration and slippage.
• Key points of eDP wiring：The differential data rate of eDP is very high (up to several Gbps), which has strict requirements for signal attenuation and reflection of wires in high-frequency environments. When designing, it is absolutely not allowed to use ordinary twisted wires. It is necessary to strictly purchase extremely thin coaxial cables (such as IPEX series micro axis plugs) with precise 100 Ω high-frequency differential impedance control, and try to shorten the signal line length within 250mm. If the line length must exceed 300mm, a high-frequency signal amplifier repeater (Redriver) must be installed to ensure absolute lossless transmission of high-speed signals.

Technical suggestions for selection：

• Prioritize LVDS：In the development or maintenance of classic industrial control devices, human-machine interfaces (HMI), classic game console terminals, outdoor large bulletin boards, and low to medium resolution systems such as 1024 x 768 or 1280 x 1024, LVDS remains the preferred choice for extremely low cost, absolutely stable supply, and mature and durable operation.

• Prioritize eDP：In the emerging development of capacitive touch all-in-one machines, medical high-resolution black and white/color image billboards, modern intelligent cockpit car screens, new generation processor direct connection architectures, and high refresh rate dynamic monitoring devices, the eDP interface with high bandwidth, neat wiring, and integrated backlight drive control is an absolute inevitable trend of the times.

1、 Anatomy of the overall structure of TFT-LCD

From a physical perspective, the imaging essence of TFT-LCD is the process in which the backlight source penetrates through layers of media and the light intensity and color are finely controlled by electronic control signals. A complete TFT-LCD module (LCM) typically consists of three core systems:

1. Backlight Unit：The "light source heart" of the screen provides a pure and uniform surface light source.
2. Electronic control switch system (TFT substrate and liquid crystal layer)：Responsible for micro precise modulation of the polarization state of light passing through each sub-pixel.
3. Color filtering system (color filter and polarizer)：Filter, dye, and ultimately convert a single ray of light into a high fidelity full-color image visible to the human eye.

2、 Deep analysis of core structure hierarchy

1. Backlight Unit/BLU - the "light source heart" of the screen

LCD itself does not have luminescent properties, it plays the role of a "light gate". The efficiency of the backlight module directly determines the screen brightness, uniformity, and service life:

• LED Array：Industrial grade screens have widely adopted LED solid-state light sources. Compared to consumer grade screens, industrial control screens usually use high-efficiency industrial grade LED chips to cope with strong outdoor light, making the screen brightness easily reach 1000 nits or even higher.
• LGP - Light Guide Plate：Using optical grade acrylic (PMMA) material, the "point/line light source" emitted by the side LED is uniformly converted into a high-efficiency "surface light source" through the bottom dot refractive microstructure.
• Diffuser & Prism Sheet：The diffusion film is responsible for eliminating the dots and unevenness on the surface of the light guide plate, making the light diffuse gently; Brightening film (prism sheet) uses micro prism structure to optically aggregate the scattered light towards the front (the axis direction of the human eye), greatly improving the display efficiency at the frontal angle.

2. Bottom Polarizer - a "polarizer" for detecting light

The light emitted by the backlight source belongs to scattered natural light with irregular vibrations. The polarizing film only allows light with specific polarization directions to pass through, filtering out scattered light into polarized light in a single direction, laying the physical foundation for the subsequent distortion modulation of liquid crystal molecules.

3. TFT Glass Substrate - Electronic Control Switch for Pixels

This is the circuit layer with the highest semiconductor integration in LCD screens: millions of thin film transistors (TFTs) and transparent pixel electrodes are manufactured on amorphous silicon (a-Si) or low-temperature polycrystalline silicon (LTPS) glass substrates through high-precision masking processes. Each red, green, and blue sub-pixel corresponds to an independent TFT. When the driver IC issues a command, the TFT switch of a specific pixel quickly conducts, precisely adjusting the voltage of that sub-pixel.

4. Liquid Crystal Layer - The Magic Switch of Light

Liquid crystals possess both the fluidity of liquids and the optical birefringence properties of crystals

• When there is no voltage：Liquid crystal molecules are arranged layer by layer in a specific initial orientation, rotating the polarization direction of polarized light by 90 ° and transmitting it over (such as the normally white mode of TN).
• When applying voltage：Liquid crystal molecules overcome their original alignment rotation and "stand up" or "translate" under strong electric fields, causing changes in their birefringence characteristics. Polarized light cannot rotate or the rotation angle is limited, thereby achieving pixel level fine control of the amount of light passing through (grayscale).

5. Color Filter/CF - The "dye box" for color

The liquid crystal layer itself can only control the brightness of light. To achieve full-color display, a color filter is attached to the opposite side of the LCD glass. Each physical pixel is composed of three sub pixels, red (R), green (G), and blue (B), arranged closely side by side. When different amounts of light through the liquid crystal layer penetrate the corresponding color filter layer, utilizing the visual color mixing effect of the human eye, up to 16.7 million (true 8-bit) or even richer colors can be synthesized by superposition.

6. Top Polarizer - The Final 'Imaging Gateway'

The polarization axis of the upper polarizer is usually orthogonal to that of the lower polarizer at a 90 ° angle. Its core function is to convert the polarized components rotated by the liquid crystal into actual changes in light intensity (bright, dark, and various shades of gray). Without the "blocking and releasing" of polarizing film, the human eye can only see a white light.

3、 Structural differences between industrial and consumer screens

Industrial applications (such as human-machine interfaces, outdoor consoles, game consoles, medical terminals) face harsh environments such as extremely low temperatures, strong earthquakes, ultraviolet radiation, and uninterrupted operation, and their structural requirements are vastly different from those of ordinary mobile phones or home televisions

4、 Practical Guide to Industrial Procurement and Selection

1. Evaluate human-computer interaction and perspective boundaries：If your device is in a scenario where multiple people are watching, looking down, or having strict side view requirements (such as bank self-service walls, wall mounted game console terminals, capacitive touch devices), IPS full view physical construction is preferred to ensure color accuracy and no water ripples when touched.

2. Quantitative planning brightness system design (to adapt to ambient lighting)：
• Pure indoor environment: A backlight system with a specification of 250~350 nits is sufficient for the application.
• Semi outdoor/low light environment by the window: 500~800 nits should be selected to ensure that the screen is not prone to whitening.
• Outdoor direct strong light: It is necessary to choose a dedicated LCD module with a brightness of over 1000 nits, equipped with high UV resistant polarizing film and reflective/transmissive semi transparent/semi reflective structure.

3. Strictly consider the long-term supply life cycle (Longevity Support)：The development cycle of industrial and special equipment often takes one year, and the service life can reach several years. Therefore, when selecting procurement models, it is necessary to choose TFT-LCD modules with industrial grade stocking mechanisms and a lifespan of at least 3-5 years, effectively avoiding the huge hidden costs of restructuring structural components and motherboard signal adapters due to screen downtime.

1、 Comparison of Microscopic Principles of Three Major LCD Panel Technologies

The essence of LCD display is to control the rotation angle of liquid crystal molecules by changing the voltage, thereby adjusting the amount of light passing through. The core difference between these three types of panels lies in the spatial arrangement and rotation of liquid crystal molecules when not powered (initial state) and powered (working state):

1. TN panel (Twisted Nematic)

• Initial state (no voltage)：Liquid crystal molecules are arranged in a horizontally twisted state (usually rotating gradually at 90 °), and light can rotate along the direction of the molecule's twist and pass through the polarizer, presenting a "normally white" state.
• Working state (applied voltage)：Liquid crystal molecules will stand up and align perpendicular to the glass substrate. At this point, the light cannot rotate and is completely blocked by the polarizing film, causing the screen to turn black.

2. VA panel (Vertical Alignment type)

• Initial state (no voltage)：Liquid crystal molecules are arranged completely perpendicular to the glass substrate. Due to the absence of any rotation in the light and the most thorough obstruction of light by vertical arrangement, it can present an extremely pure black color, presenting a "normally black" state.
• Working state (applied voltage)：Liquid crystal molecules deflect in a tilted direction, allowing some light to pass through and form grayscale.

3. IPS panel (In Plane Switching)

• Initial state (no voltage)：The liquid crystal molecules are arranged completely parallel to the glass substrate, and light cannot pass through, also belonging to the "normally black" design.
• Working state (applied voltage)：Liquid crystal molecules rotate horizontally like propellers in a plane parallel to the substrate. This is its most core physical feature - no matter how the voltage changes, the liquid crystal molecules always remain parallel to the substrate.

2、 Multi dimensional in-depth evaluation of core performance indicators

1. Viewing Angle: The underlying logic of a 178 ° panoramic view

At industrial sites or public terminals, operators often need to view the screen from the side or pitch angle, which places extremely high demands on the viewing angle:

• TN (narrow viewing angle)：The viewing angle is usually only 90 °/50 ° (left/right/up/down). When viewed from below or from the side, there is a severe color inversion and brightness drop in the image, known as the 'death angle'.
• VA (Wide View Angle)：It can reach 170 °/170 °, but there may still be a slight "color wash out" in contrast and color saturation when viewed at large angles.
• IPS (True Full View)：Due to the constant rotation of liquid crystal molecules in the horizontal plane, the optical properties at various angles are highly consistent, truly achieving a full viewing angle of 178 °/178 °. Whether viewed from extreme left, right, top, or bottom angles, there is almost no deviation in color and brightness of the image.

2. Contrast Ratio: Ultimate Profound in the Dark Night

•VA ruling field：When there is no voltage, VA panels have the most thorough vertical light blocking of liquid crystal molecules, minimal light leakage, and a static contrast ratio usually as high as 3000:1 to 5000:1. The black screen is extremely deep, with delicate details in the dark areas, making it very suitable for the medical imaging and large screen monitoring industries that have strict requirements for dark details.
• IPS is slightly inferior to TN：IPS has natural physical light leakage (IPS Glow), and the static contrast ratio is usually 1000:1 (some high-end can reach 1500:1); TN screens are the worst, usually only 700:1~1000:1.

3. Response Time: The smoothness of dynamic images

Response time is divided into "rise time" and "fall time", usually measured by gray response time (GtG - Gray to Gray):

• TN is absolutely leading：The twisted and restored motion path of liquid crystal molecules is extremely short, with a response time as low as 1ms. It is widely used in esports and high-speed industrial visual inspection.
• IPS centered：The response time is generally around 3ms-5ms, and with Overdrive drive technology, it is sufficient to handle the vast majority of industrial and entertainment images that combine motion and stillness.
•VA bottom：The process of vertical liquid crystal molecules standing up and lying down is slow, and the GtG response time is usually between 8ms and 15ms. It is also prone to "black smearing" when displaying dark dynamic images, resulting in poor presentation of high-speed dynamic images.

3、 Pain points of "physical hardness" and "environmental temperature range" in industrial application scenarios

1. Screen Physical Contact: Hard Screen (IPS) vs Soft Screen (VA/TN)

In public query all-in-one machines, touch screen devices, or game consoles, the screen is inevitably frequently pressed and touched by fingers. The following table shows their reactions upon physical contact:

2. Wide Temperature

Industrial environments are often accompanied by extreme high or low temperatures (such as -20 ° C to 70 ° C).
The technology development of IPS and VA panels is more mature, which can use highly stable industrial wide temperature liquid crystal materials, effectively avoiding the occurrence of "isotropy" of liquid crystal at high temperatures (liquid crystal turning back to ordinary liquid causing the screen to turn black over a large area) or crystal failure at low temperatures. This fundamentally guarantees their stable operation in extreme outdoor environments.

4、 Ultimate benchmark table for industry selection

5、 Summary and Procurement Suggestions

• Select IPS panel：If your product is a capacitive touch all-in-one machine, mid to high end gaming equipment, medical equipment, outdoor query terminal, and places great emphasis on wide viewing angles and undistorted colors, IPS is an uncompromising standard configuration.

• Select VA panel：If you are developing static large screen monitoring systems or information publishing large screens that require extremely high contrast and dark details, VA has the highest cost-effectiveness.

• Select TN panel：If it is a low-end embedded header with pure numerical display and extreme cost sensitivity, TN panel is still a powerful tool to reduce BOM costs.

1、What is Light Guide Plate (LGP)?

What does LGP look like? The Chinese name for LGP (Light Guide Plate) is (Light Guide Plate)

The light guide plate is usually an optical grade acrylic board (PMMA) or polycarbonate board (PC). Its surface is very smooth, looking like an ordinary transparent plastic board. But its magic lies in that when light enters from its side, it can lock these lights and let them propagate forward along the board, finally accurately and evenly "shooting" out from the front.

1. The following diagram shows the disassembly of the entire LCD module, with the fifth layer being the LGP (Light Guide Plate)

2、Scope of use for LGP

1. Mobile phones, tablets, laptops, car displays, industrial controls, displays, televisions, flat panel lights, and other fields.

3：Precautions

1、LGP is only used for LCD products, OLED products do not require it

2、What does the LGP actually look like? The following figure shows common forms of LGP, each corresponding to different application scenarios.

4：The core working principle of light guide plate

The reason why light guide plates can achieve "side light in and front light out" mainly depends on two physical phenomena: total internal reflection and light scattering.

1. Locking Light: Total Reflection Principle

When the light from the side LED light source enters the light guide plate, the light will propagate forward inside the light guide plate. Due to the significantly higher refractive index of acrylic board (about 1.49) compared to the surrounding air (1.0), according to optical principles, total reflection occurs when light is directed towards the upper and lower surfaces of the light guide plate at a large angle.

Result: Light bounces forward inside the light guide plate like in a mirror maze, without leaking out from the surface. If there is no other interference, the light will continue to reach the end of the light guide plate.

2. Breaking the balance: dot destruction total reflection

If all the light is locked inside, the screen will naturally not light up. In order to make the light "obediently" emit from the front, engineers have designed many tiny structures on the bottom of the light guide plate, which are called light guide dots.

Microstructure： These outlets can be produced through methods such as ink printing, laser engraving, or injection molding, and they can be small pits, protrusions, or prism structures.

Disrupting total reflection： When the light transmitted inside the board hits these dots, the reflection angle will change and no longer meet the condition of total reflection. The light then "refracts" out of the dot and reflects upwards again through the reflector below the light guide plate, ultimately penetrating the front of the light guide plate and shooting towards the liquid crystal panel.

5、 How to achieve 'complete uniformity'? (Network density design)

This is the most core process in light guide plate technology. We know that when light enters from the side, the light is stronger near the light source and weaker away from it. If the dots at the bottom of the light guide plate are evenly distributed, the screen will experience an awkward phenomenon of "extremely bright on the edges and extremely dark in the middle".

In order to achieve a perfect visual experience, the dot design of the light guide plate adopts a dynamic layout of "near distant dense":

Through this precise calculation of geometric distribution, the light guide plate successfully transforms uneven side edge light sources into uniform surface light sources with highly consistent brightness throughout the surface.

Below：

By using light guide points of various sizes/densities, the light guide plate emits light uniformly.

1、Material of light guide plate

Firstly, raw materials are the most significant factor affecting the price of light guide plates. Generally speaking, the market mainly uses PS (polystyrene), PC (polycarbonate) type (high temperature resistance, impact resistance), composite substrate type, and PMMA (acrylic) type (light transmittance>92%, the most mainstream) as the substrate for light guide plates. Due to the optical properties of these three materials, especially the wide range of light transmittance differences, as well as their physical properties, weather resistance, UV resistance, and other aspects, the price difference between these three raw materials is also relatively large

It has excellent optical properties comparable to optical glass, with a refractive index similar to optical glass, hence it is called optical plastic. PMMA has the advantages of light weight, low cost, and easy molding. Its molding methods include casting, injection molding, mechanical processing, and hot injection molding. It can be produced in large quantities, with a simple process and low cost. Therefore, its application is becoming increasingly widespread, such as billboards, skylights, fluorescent lampshades, and doors and windows of transportation vehicles

6：Reflection Law&Refraction Law

1、Law of reflection：θi  = θr     

a，The vertical normals of the incoming, outgoing, and reflecting surfaces are all in the same plane.

b，Assuming that light waves travel in a straight line direction

2、Law of refraction

a、 The speed of light varies in different media.

b、 The speed of light is maximum in vacuum.

c、 Index of Refraction:

7：Light guide plate dot

Light guide plate layout method: equal diameter density, equidistant size

      Generally, LED side dots are sparse (small), while the output side dots are dense (large)

 ps：The energy of the outgoing side light is getting weaker and weaker, requiring the use of more dots to reflect the light

8、Summary

The light guide plate is like an efficient light dispatcher. It uses total reflection to lock the light from the side LED inside the body for long-distance transportation, and then uses the microscopic dots at the bottom to precisely destroy total reflection, allowing the light to continuously project from the front according to the scientific law of "near distance, far distance, and dense".

Without the precise light control of the light guide plate, there would be no world of thin, energy-efficient, and high-quality LCD displays today.