lcd Related Articles

Introduction There are many kinds of LCD interfaces, with wide range of applications. The classification criteria mainly depends on the driving mode and control mode of the LCD. At present, there are generally several connection modes for color LCDs on mobile phones: MCU mode, RGB mode, SPI mode, VSYNC mode, MDDI mode, DSI mode, etc. and only the TFT module has RGB interface. Basics of LCD Interfacing Catalog Introduction Ⅰ LCD Interface Modes 1.1 MCU Mode 1.2 VSYNC Mode 1.3 M6800 Mode 1.4 Intel 8080 Mode 1.5 RGB Mode 1.6 SPI (Serial Peripheral Interface) Mode 1.7 MDDI (Mobile Display Digital Interface) Mode 1.8 DSI (Display Serial Interface) Mode Ⅱ MCU Mode vs RGB Mode Ⅲ TFT-LCD Interface Explained 3.1 TTL Interface 3.2 LVDS 3.3 EDP (Embedded Display Port) 3.4 MIPI Interface Ⅳ FAQ Ⅰ LCD Interface Modes The following is a detailed explanation of the different interface modes: 1.1 MCU Mode It is mainly used in the field of single-chip microcomputers. Later, it is widely used in low-end mobile phones, and its main feature is that it is cheap. The standard term for the MCU-LCD interface is the 8080 bus standard proposed by Intel. Figure 1. Intel 8080 Therefore, 8080 is used to refer to the MCU-LCD screen in many documents. It can be mainly divided into 8080 mode and 6800 mode, and the difference between the two is mainly the timing. There are 8 bits, 9 bits, 16 bits, 18 bits, and 24 bits for data bit transfer. Connections are divided into: CS/, RS (register selection), RD/, WR/, and data lines. The advantages are: the control is simple and convenient, no clock and synchronization signals are required. The disadvantage is: it consumes GRAM, so it is difficult to achieve a large screen (above 3.8). For LCM with MCU interface, the internal chip is called LCD driver. The main function is to transform the data/command sent by the host into the RGB data of each pixel, so that it can be displayed on the screen. This process does not require point, line, frame clocks.The LCD Driver IC of the MCU interface is equipped with GRAM. As a co-processor of the MCU, it accepts the Command/Data sent by the MCU and can work relatively independently. Pay attention to, the internal chip of LCD Module (LCM) is called the LCD driver. The main function is to transform the data/commands sent by the host computer into the RGB data of each pixel, so that it can be displayed on the screen. This process also does not require point, line, frame clocks. 1.2 VSYNC Mode In fact, this mode is to add a VSYNC signal to the MCU mode and applied to the update of the moving picture, which is very different from the above interface. This mode supports the function of direct animation display. It provides a solution for animation display with minimal changes to the MCU interface. In this mode, the internal display operation is synchronized with the external VSYNC signal. Animation display at a higher rate than internal operations can be achieved. However, due to the difference in its operation mode, this mode has a limit on the speed, that is, the write speed to the internal SRAM must be greater than the speed of the display read internal SRAM. 1.3 M6800 Mode The M6800 mode supports selectable bus widths of 8/9/16/18-bit (the default is 8 bits). The actual design idea is the same as that of Intel 8080. The main difference is the bus control read and write signals in this mode. Combined on one pin (with a latch signal (E) data bit transmission has 8, 9, 16 and 18 bits). Figure 2. M6800 Mode 1.4 Intel 8080 Mode Intel 8080 LCD interface is divided into: CS/, RS (register selection), RD/, WR/, and the data line. Advantage: Simple and convenient control, no clock and synchronization signals are required. Disadvantage: It consumes GRAM, so it is difficult to achieve a large screen (above QVGA). Figure 3. Intel 8080 Mode 1.5 RGB Mode The large screen adopts more modes, and the data bit transmission also has the 6-, 16- and 18-, 24-bit. The connections are generally: VSYNC, HSYNC, DOTCLK, CS, RESET, some also need RS, and the rest is the data line. Its advantages and disadvantages are just the opposite of MCU mode. The main difference between the MCU-LCD screen and the RGB-LCD screen is the location of the video memory. The video memory of RGB-LCD is acted by system memory, so its size is only limited by the size of system memory. Where RGB-LCD can be made larger, such as 4.3" can only be regarded as entry-level, and 7" in MID, 10" screens have begun to be widely used. At the beginning of the design of MCU-LCD, it was only necessary to consider that the memory of the single-chip microcomputer was small, so the video memory was built into the LCD module, and then the software updated the video memory through special display commands with small MCU screen. At the same time, the display update speed is slower than RGB-LCD. The display data transmission mode is also different. RGB screen only needs to organize the data in the video memory. After starting the display, the LCD-DMA will automatically transfer the data in the video memory through the RGB interface to the LCM, while the MCU screen needs to send a drawing command to modify the internal RAM of the MCU (that is, the RAM of the MCU screen cannot be directly written).Therefore, the RGB display speed is significantly faster than that of the MCU, and the MCU-LCD is also slower in terms of video playback. For the LCM of the RGB interface, the host directly outputs the RGB data of each pixel without conversion (except for GAMMA correction, etc.). For this interface, an LCD controller is required in the host part to generate RGB data and sync signals. Figure 4. RGB Mode Here gives a note. The color TFT LCD screen mainly has 2 kinds of interfaces: TTL interface (RGB color interface), and LVDS interface (differential signal transmission). The TTL interface is mainly used for small-sized TFT screens below 12.1 inches, and the LVDS interface is mainly used for large-sized TFT screens above 8 inches. The TTL interface has many lines and the transmission distance is short, while the LVDS interface has a long transmission distance and a small number of lines. The large screen adopts more modes, the control pins are VSYNC, HSYNC, VDEN, VCLK, S3C2440 supports up to 24 data pins, and the data pin is VD[23-0].The image data sent by the CPU or graphics card is a TTL signal (0-5V, 0-3.3V, 0-2.5V, or 0-1.8V), and the LCD itself also receives a TTL signal, which is transmitted at a high rate over long distances. However, its performance is poor, and the anti-interference ability is relatively poor. With the time goes by, a variety of transmission modes were proposed, such as LVDS, TDMS, GVIF, P&D, DVI and DFP. They actually just encode the TTL signal sent by the CPU or graphics card into various signals for transmission, and decode the received signal on the LCD side to obtain the TTL signal. No matter what transmission mode is used, the essential TTL signal is the same. Note: TTL/LVDS are two signal transmission modes: TTL is a mode in which high level means 1, and low level means 0; LVDS is the difference of a positive and negative corresponding waveform used to indicate the 1 or 0. 1.6 SPI (Serial Peripheral Interface) Mode It is less used. There are 3-wire and 4-wire, the connection is CS/, SLK, SDI, and SDO, and the software control is more complicated. 1.7 MDDI (Mobile Display Digital Interface) Mode  Qualcomm's MDDI, which can improve the reliability of mobile phones and reduce power consumption by reducing wiring. It will replace SPI mode as a high-speed serial interface in the mobile field. The main connection is host_data, host_strobe, client_data, client_strobe, power, and GND. 1.8 DSI (Display Serial Interface) Mode This mode is a serial bidirectional high-speed command transmission mode, with D0P, D0N, D1P, D1N, CLKP, CLKN connected.   Ⅱ MCU Mode vs RGB Mode Among them, there are more applications in MCU mode and RGB mode. The differences are as follows:1) MCU interface: it will decode commands, generate timing signals by timing generator, and drive COM and SEG.RGB interface: When writing LCD register setting, it is no different from MCU interface. The difference is only in how the image is written.2) When using the MCU mode, since the data can be stored in the IC's internal GRAM first and then written to the screen, the LCD in this mode can be directly connected to the memory bus. It is different when using RGB mode, and has no internal RAM, HSYNC, VSYNC, ENABLE, CS, RESET, RS can be directly connected to the GPIO port of memory, and use the GPIO port to simulate waveforms.3) MCU Interface vs RGB InterfaceThe main differences between the MCU interface and the RGB interface are:MCU interface mode: display data is written into DDRAM, often used for still picture display.RGB interface mode: The display data is not written into DDRAM, but directly written to the screen, which is fast and often used to display video or animation.   Ⅲ TFT-LCD Interface Explained The commonly used interfaces of TFT-LCD, including TTL (RGB), LVDS, EDP, and MIPI. Here roughly talk about the basic principles of the signal composition of these interfaces. Figure 5. TTL (Transistor-Transistor Logic) Schematic 3.1 TTL Interface 🔺Interface OverviewTTL is transistor-transistor logic, and TTL level signals are generated by TTL devices. TTL devices are a large category of digital integrated circuits. They are manufactured by bipolar technology and have the characteristics of high speed, low power consumption and many varieties.The TTL interface is an interface for transmitting data in parallel. When using it, it is not necessary to use a dedicated interface circuit at the driver board end and the LCD panel end of the liquid crystal display, but the TTL data signal output by the main control chip of the driver board is transmitted through the cable. It is directly transmitted to the input interface of the LCD panel. Due to the high signal voltage, many connections and long transmission cables of the TTL interface, the anti-interference ability of the circuit is relatively poor, and it is easy to generate electromagnetic interference (EMI). In practical applications, TTL interface circuits are mostly used to drive small-size (below 15in) or low-resolution LCD panels. The highest pixel clock of TTL is only 28MHz.TTL is the only signal that TFT-LCD can recognize. Early digital processing chips are all TTL, that is, RGB is directly output to TFT-LCD.🔺Signal TypesThe TTL output interface of the driver board generally includes three types of signals: RGB data signal, clock signal and control signal. As shown below:(1) RGB Data-Signala. Single Channel6-BitAs for it, there are 18 RGB data lines in total, including 6 R0~R5 red primary color data lines, 6 G0~G5 green primary color data lines, 6 B0~B5 blue primary color data lines, a total of 18 strips. Since the primary color RGB data is 18bit, it is also called 18-bitTTL interface.8-BitFor it, there are a total of 24 RGB data lines, including 8 R0~R7 red primary color data lines, 8 B0~B7 green primary color data lines, 8 BO~B7 blue primary color data lines, a total of 24 strips. Since the primary color RGB data is 24-bit, it is also called 24-bit TTL interface.b. Dual ChannelDual channels, that is, two sets of RGB data, which are divided into odd channels and even channels. Some clocks are also divided into OCLK/ECLK, and some share one. The following figure has two, as shown below:6-BitIt has 36 RGB data lines in total, including 18 odd RGB data lines, 18 even RGB data lines. Since the primary color ROB data is 36-bit, it is also called 36-bitTTL interface.8-BitIt has 48 RGB data lines, including 24 odd RGB data lines and 24 even RGB data lines. Since the primary color RGB data is 48bit, it is also called 48-bit TTL interface.(2) Clock SignalIt refers to the pixel clock signal, which is the benchmark for transmitting data and reading the data signal. When using odd/even pixel dual way to transmit RGB data, different output interfaces use different methods of pixel clock. Some output interface odd/even pixel dual data share a pixel clock signal, and the others set odd pixel data clock and even pixel two clock signals to meet the needs of different LCD panels.(3) Control SignalThe control signals include a data enable signal (or an effective display data strobe signal) DE, a horizontal sync signal HS, and a vertical sync signal VS. 3.2 LVDS 🔺Overview of LVDS InterfaceLVDS is a low-voltage differential signaling technology interface. A digital video signal transmission method developed to overcome the shortcomings of large power consumption and large EMI electromagnetic interference when transmitting broadband high bit rate data in TTL level mode. The LVDS output interface uses a very low voltage swing (about 350mV) to transmit data differentially on two PCB traces or a pair of balanced cables, that is, low-voltage differential signaling. Using the LVDS output interface, the signal can be transmitted at a rate of several hundred Mbit/s on the differential PCB line or balanced cable. Due to the low-voltage and low-current driving method, low noise and low power consumption are achieved.🔺Composition of LVDS Interface CircuitIn a liquid crystal display, the LVDS interface circuit includes two parts, the LVDS output interface circuit (LVDS transmitter) on the motherboard side and the LVDS input interface circuit (LVDS receiver) on the LCD panel side. The LVDS emitter converts the TTL signal into an LVDS signal, and then transmits the signal to the LVDS decoding IC on the receiving end through the flexible cable (line) between the driver board and the LCD panel, and the LVDS receiver then serializes the serial signal which is converted into a parallel signal of TTL level, and sent to the LCD screen timing control and row and column drive circuit. In other words, TFT only recognizes TTL (RGB) signals.🔺Signal type of LVDS interfaceLVDS signals are composed of data differential and clock differential signals. As shown below:(1) Single Channel6-Bit DataThere are 4 sets of differential lines, 3 sets of signal lines, and one set of clock lines, including Y0M, Y0P, Y1M, Y1P, Y2M, Y2P, CLKOUT_M, CLKOUT_P.8-Bit DataThere are 5 groups of differential lines, 4 groups of signal lines, and a group of clock lines. They are Y0M, Y0P, Y1M, Y1P, Y2M, Y2P, CLKOUT_M, CLKOUT_P.(2) Dual ChannelWhen LVDS transmits data with higher resolution, the anti-interference ability is relatively strong. But when the resolution is higher than 1920×1080, the single channel is overwhelmed, so there is a dual interface. Its purpose is very simple, speed up and enhance anti-interference ability.6-Bit DataIt is exactly twice as long as the single channel, and the clock is also two channels. The red part: the two sets of signals: Y3M, Y3P, Y3M1, and Y3M1 are not connected.8-Bit DataSimilar to the previous comparison. 3.3 EDP (Embedded Display Port) EDP is a communication interface of the computer display screen. The resolution of the computer using the EDP display interface will be higher than that of the LVDS interface. Generally, high-definition screens use this communication interface. It is a fully digital interface based on the DisplayPort architecture and protocol. It can transmit high-resolution signals with simpler connectors and fewer pins, and can achieve simultaneous transmission of multiple data, so the transmission rate is much higher than LVDS. 3.4 MIPI Interface Compared with the LVDS interface, the MIPI interface is rare, but in fact, it has many advantages. The MIPI interface module has the advantages of high speed, large amount of data transmission, low power consumption, and good anti-interference when compared with the parallel port. It is more and more favored by customers and is growing rapidly. For example, an 8M module with both MIPI and parallel port transmission requires at least 11 transmission lines and an output clock of up to 96M to achieve a full pixel output of 12FPS when using an 8-bit parallel port. Channel 6 transmission lines can achieve a frame rate of 12FPS at full pixels, and the current consumption will be about 20MA lower than that of parallel port transmission. Since MIPI uses differential signal transmission, the design needs to be strictly designed according to the general rules of differential design. The key is to achieve differential impedance matching. The MIPI protocol stipulates that the differential impedance of the transmission line is 80-125 ohms.   Ⅳ FAQ 1. What is LCD interface?16x2 LCD means that there are two rows in which 16 characters can be displayed per line, and each character takes 5X7 matrix space on LCD. ... In this tutorial we are going to connect 16X2 LCD module to the 8051 microcontroller (AT89S52). 2. What is LCD parallel interface?LCD Displays that use a parallel interface include Character, Graphic and TFT. ... The initial step is to energize the LCD. Reads and Writes are sent via 8 data lines and 3 control lines. These control lines are Read/Write (R/W), Enable (E) and Register Select (RS). 3. What is TFT interface?A TFT LCD display module consists of a TFT LCD panel, one or more COG (chip-on-glass) or COB (chip-on-board) driver ICs, a backlight, and an interface. Several TFT display interface technologies exist today. Picking the right interface depends on specific end-product concerns. 4. What are the different types of LCDs?Different Types of LCD PanelsTwisted Nematic (TN) Twisted Nematic LCDs are the most commonly manufactured and used types of monitors across a wide range of industries. ...IPS Panel TechnologyVA PanelAdvanced Fringe Field Switching 5. What is MCU interface?The MCU interface has two standard types, the Intel-8080 and Motorolla-6800 series. These interfaces communicate through read, write and chip-select signals to address registers or display RAM. The slight difference between the two pertains to the direction and separation of the write and read signals. 6. What is MCU interface LCD?These interfaces communicate through read, write and chip-select signals to address registers or display RAM. Depending on color depth (8, 9, 16 or 18-bit), MCU sends RGB signals directly to LCM's display memory. 7. Is TFT an LCD?TFT is a kind of LCD. The TFT(Thin Film Field-effect Transistor) is a video in which every single pixel in the liquid crystal display is actuated by a Thin Film Transistor embedded in the rear. Thus can achieve high speed, high brightness, high contrast display screen information.

Warm hints: The word in this article is about 3000 words and reading time is about 15 minutes   This article is mainly talking about how to design better electromagnetic compatibility if LCD. Electromagnetic compatibility (EMC) is an inevitable issue in the design of LCDs. If the EMC design is not good, it will cause water ripples and strobe flash problems during the broadcast of the TV. EMC design is actually optimized for the electromagnetic interference generated in the product to meet the EMC standards of countries or regions. It is defined as the ability of a device or system to function properly in its electromagnetic environment and does not constitute unacceptable electromagnetic interference (EMI) to anything in the environment.       Catalog I. Brief Introduction II. Power Module EMC Design III. Main Drive Board EMC Design IV. Tuner Board EMC Design V. Whole Machine EMC Design FAQ   I. Brief Introduction Electromagnetic interference is generally divided into conducted interference and radiation interference. Conducted interference refers to the coupling interference of signals on one electrical network to another electrical network through conductive media. Radiated interference means that the interference source couples (disturbs) its signal to another electrical network through space.   The LCD structure mainly includes a liquid crystal display module, a power supply module, a drive module (mainly including the main drive board and a tuner board), and a key button module. General liquid crystal display modules have been tested by EMC before production. Here mainly introduces the design of the power module, drive module, button module, and the whole machine should pay attention to the electromagnetic interference problem.   EMI (ElectroMagnetic Interference) & EMC (Electromegetic Compatibility)   II. Power Module EMC Design The two main functions of the power supply section are to realize the backlight for driving the LCD screen and to provide DC power for other modules (including the drive module and the button module).   The design of the power module directly affects the entire system. If the design is not good, it will cause large water ripples in the TV. In severe cases, the TV will not be used. At the same time, it will seriously affect the normal use of other nearby equipment.   The power supply of LCDs is based on switching power supplies. The causes of electromagnetic interference problems caused by switching power supplies are complex. When designing the switching power supply, it is necessary to prevent the switching power supply from causing interference to the power grid and nearby electronic equipment. It is also necessary to strengthen the adaptability of the switching power supply itself to the electromagnetic interference environment.   To solve the EMC problem of switching power supplies, the following main measures should be taken into consideration during design:   Soft-switching technology: Inrush current and peak voltage are generated when the switching device is turned on/off. This is the main reason for electromagnetic interference and switching loss in the switch. Soft switching technology is an important method to reduce the loss of switching devices and improve the EMC characteristics of switching devices. This technology is mainly to switch the switching tube in the switching power supply at zero voltage and zero current to effectively suppress electromagnetic interference.   Modulation frequency control: Electromagnetic interference is changed according to the switching frequency, and the interference energy is concentrated on the discrete switching frequency point, resulting in large interference intensity. By distributing the energy modulation of the switching signal over a wide frequency band, a series of discrete sidebands are generated. This spreads out the interference spectrum, and the interference energy is distributed on the discrete frequency band, thereby reducing the electromagnetic interference intensity at the switching frequency point.   Component layout and routing: The components associated with the power input signal and output signal are placed near the corresponding ports to avoid interference due to the coupling path. Put components that are related to each other together to avoid interference caused by long traces.   Also, try to avoid parallel routing of signal lines. If unavoidable, try to increase the line spacing. Or add a ground wire in the middle to reduce the interference between each other.   III. Main Drive Board EMC Design The main driver board of the LCD mainly includes an analog signal portion, a high-speed digital circuit portion, and a noise source DC-DC power supply portion.   Component layout and routing: In the layout, the three parts of the analog signal part, the high-speed digital circuit part, and the noise source DC-DC power supply part should be reasonably separated so that the signal coupling between them is the minimum. In terms of device placement, the principle of associating the devices with each other is as close as possible, so that a good anti-noise effect can be obtained.   DC-DC Power Supply Part and Ground: On printed circuit boards, the power line and ground are the most important. Let analog and digital circuits have their own power and ground paths, respectively. The main means of overcoming electromagnetic interference is grounding.   On the driving board of the LCD, the ground of the power supply section (DC-DC) is mainly separated from other grounds such as the decoding and main chip processing, so as to reduce interference of the power supply on the image display and the television sound.   If there are analog ground and the digital ground when designing the circuit, they should be separated when the printed board is laid. To reduce mutual interference. In the layout of double-layer boards and multilayer PCBs, one layer of copper foil is generally used as a dedicated ground plane. The purpose of this is that this ground serves as a shield.   Integrated chip: In the same integrated chip, the ground is also separated from the analog ground and the digital ground. For example, the AD9883 analog-to-digital conversion chip of the AD company, which is often used as the main driver board of the LCD, can be floor-separated between the ground and digital sections of the analog section of the chip during the PCB design. Finally, connect the two points by a relatively short wire. Or connect the two places with a 1nF bypass capacitor.   Crystal oscillator: The clock circuit in the digital circuit is one of the main electromagnetic interference sources in current electronic products and is the main content of EMC design. Crystal is a strong source of radiation. The internal circuit of the crystal generates a large RF current, so that the ground lead of the crystal cannot sufficiently draw a relatively large Ldi/dt current to the ground plane with little loss, and as a result, the metal housing becomes a monopole antenna. The periphery of the crystal is a radiation field.   Therefore, the crystal oscillator circuit is far away from the interface circuit, such as serial port, address line, and data line. In order to avoid the interface circuit bringing the harmonic signal of the crystal out of the printed circuit board to cause electromagnetic interference. Two legs of the crystal oscillator must be added with an RC filter circuit. At the same time, be sure to connect the metal shell of the crystal to the ground on the printed board. In addition, the crystal is placed as close as possible to the chip pins. The ground is used to isolate the clock area, placing a local ground plane and connecting it to the ground through multiple vias.   Capacitance decoupling: Capacitance decoupling is used to reduce electromagnetic interference. Capacitor decoupling can be divided into three types: overall, partial, and inter-board.   The overall decoupling capacitor operates at low frequencies, providing a stable voltage and current for the entire board. It should be placed close to the printed circuit board power cord and ground. The typical decoupling capacitor value is 0.1μF. The typical value of the distributed inductance of this capacitor is 5μH. The 0.1μF decoupling capacitor has 5μH distributed inductance. Its parallel resonant frequency is about 7MHz. That is to say, it has a better decoupling effect for noise below 10MHz, and it has almost no effect on noise above tens of MHz. So for noise above 20MHz, use a 0.01μF capacitor decoupling.   The local decoupling capacitor makes the supply voltage obtained by the integrated circuit more stable; in addition, the high-frequency noise of the device is bypassed.   The decoupling capacitance between boards refers to the capacitance between the power plane and the ground plane and mainly solves the high-frequency transient current generated in the power supply. A 10~100uF electrolytic capacitor is connected across the input of the power supply. If the position of the printed circuit board is allowed, the anti-interference effect of the electrolytic capacitor with 100uF or more will be better. The lead of the decoupling capacitor can not be too long, generally close to the integrated circuit power supply, the connection should be rougher.   Bead filtering: Bead filtering is applied to all signal inputs (such as YPBPR and VGA) on the motherboard. Magnetic beads are designed to suppress high-frequency noise and spike interference on signal lines and power lines, and also have the ability to absorb electrostatic pulses. It acts as a high-frequency resistor, which attenuates high frequencies. The device allows the DC signal to pass and filter out the AC signal.   When selecting beads, you must pay attention to the following factors:   1. What is the unwanted signal frequency range? 2. Who is the noise source; 3, how much noise attenuation; 4. What is the environmental condition (temperature, DC voltage, structural strength); 5. What is the circuit and load impedance? 6. Is there room to place beads on the PCB board?   The first three can be judged by observing the impedance frequency curve provided by the manufacturer. The three curves in the impedance curve are very important, namely the resistance R, inductive reactance X, and total reactance Z. As shown in Figure 1:     Figure 1: Impedance curve and equivalent circuit topology that reflect the bead resistance, inductive reactance, and total inductance   The total impedance is described by the following formula (1):   Z=(R + 2πFL)   From this curve, beads are selected that have the maximum impedance in the frequency range where attenuation of the noise is desired, and where the attenuation of the signal is as small as possible at low and DC.   Chip beads can affect the impedance characteristics under excessive DC voltage. In addition, if the operating temperature rises too high or the external magnetic field is too large, the impedance of the beads will be adversely affected.   Whether using chip beads or chip inductors is also mainly in applications. Chip inductors are needed in the resonant circuit. When it is necessary to eliminate unwanted electromagnetic interference noise, the use of chip beads is the best choice.   IV. Tuner Board EMC Design The tuner board mainly includes a tuner section and an audio processing section.   When conducting the circuit design of the tuner board part and the layout of the PCB board, it is necessary to pay special attention to the electromagnetic interference problem. The following points must be considered:   （1）First, separate the land of the TUNER section (ie the simulated ground) from the land of the other sections. （2） Be sure to connect the metal shell of TUNER to the ground. The connection points can better eliminate electromagnetic interference. The tuner TUNER inherently has a high-frequency circuit, so it must be shielded. （3）When selecting the interface terminals (such as AV terminal, S-VIDEO terminal, etc.), try to use terminals with good conductivity and strong anti-electromagnetic interference, and also connect the ground of the interface terminal with the earth completely. At the same time also added magnetic beads filter. （4）The signal line should be as short and straight as possible. If it cannot be avoided, fly line transitions can be used. Signal lines should not form a ring. Because the ring is equivalent to the number of turns of the coil, the radiation effect of the ring wiring is the strongest. （5）Try to reduce dead copper in large areas. The solution is to connect them to the ground. If a large area of dead copper forms the antenna, electromagnetic interference will be introduced. （6）Do not run under quartz crystals and under noise-sensitive devices.   The audio processing section should pay special attention to the layout of the printed circuit board, first of all, avoid high-speed signal lines and audio and video lines together. For example, if you connect the clock line SCL and the data line SDA in the I2C bus to the traces of the audio line. Since the clock line SCL and the data line SDA in the I2C bus are constantly changing, they interfere with the sound. Obviously, for example, when you use a TV remote control to switch to a TV channel, you can hear a regular "click, click" sound from the speaker. This may be because of the above issues that were overlooked in the PCB layout.     V. Whole Machine EMC Design   The assembly drawing in the whole machine (taking one of the models as an example) is shown in Figure 2: Figure 2: In-machine assembly drawing of a model that reflects various EMI concerns   The connection line numbered 5 in the figure above is the screen line of the digital panel connection screen. Because the screen line is mainly on the screen data. It will cause a great disturbance to the system. The best way to reduce interference is to use twisted pairs and shielded wires. If it is a TTL screen, the screen line needs to be shielded or a magnetic ring outside the connection line. If on the LVDS screen, you need to use twisted pair, plus a magnetic ring. In order to reduce the screen line to the entire system of electromagnetic interference. With shielded twisted pair, the signal current can flow on the two inner conductors, and the noise current flows in the shield layer, thus eliminating the coupling of the common impedance, and any interference will induce the two conductors at the same time so that the noise cancels.   A magnetic ring is also required on the connection between the power supply and the main control board (referenced 4). The main reason is that the power cord will generate relatively large electromagnetic interference to the motherboard.   A magnetic ring should also be added to the connection between the keypad and the motherboard (referenced 9). The main reason is that there is a constant data change (remote control receiver head) on the keypad which causes electromagnetic interference to the system. Plus magnetic rings can effectively shield electromagnetic interference.   A magnetic ring is added to the audio cable (labeled 10) connected to the speaker to reduce the electromagnetic interference from the audio output to the system. If there is a cable (label 6, 7, 8) between the motherboard and the tuner board, you need to add a magnetic ring on the cable. To reduce the electromagnetic interference between cables.   The magnetic ring added above can be added according to the specific situation and can be determined by repeated experiments.   Use of shields: In general, shields are required for liquid crystal display modules, main control boards (including digital boards and tuner boards), and power supplies.   The main frequency of the main chip is the main cause of electromagnetic interference. Frequency harmonics of the main frequency are most likely to produce electromagnetic interference. In the experiment conducted by EMC, the frequency harmonics of the main frequency had large electromagnetic interference. The main chip must be shielded during design. The main shielding measures include a metal shield on the digital board. Adding a shield is the most effective way to resist electromagnetic interference. However, because of the heat dissipation problem of the driver board and the entire system, it is required that the holes on the shield cover be used to dissipate heat. However, its maximum size must be less than 1/100 of the shortest wavelength of noise.   The shield on the tuner board is mainly shielded from the TUNER section.   The shielding of the power supply section is particularly important. If the shielding of the power supply section is not good, it will cause large interference. This will not lead to conduction. And because the heat of the power supply is very severe, the shield must pay attention to the problem of heat dissipation.   Usually, shields have openings and seams that can cause electromagnetic leaks. As a result, the shielding effect is not good. Solve electromagnetic leaks at joints by using electromagnetic seal gaskets at the joints. The electromagnetic leakage of the opening in the shield is related to the size of the opening, the characteristics of the radiation source, and the distance from the radiation source to the opening. The requirement for shielding is met by designing the size of the opening and the distance of the radiation source to the opening. FAQ   1. What can cause electromagnetic interference? Electromagnetic interference (EMI) is a disturbance caused by an electromagnetic field which impedes the proper performance of an electrical device. EMI can come from man-made or natural sources such as the sun or the Earth's magnetic fields.   2. How do you stop electromagnetic interference? The simplest way to reduce magnetically induced interference is to use twisted pair wires. This applies both for shielded and unshielded cables and for interference caused by shield currents or from other sources. Twisting the wires forces them close together, reducing the loop area and therefore the induced voltage.   3. How do you make electromagnetic interference? Plug both devices into a wall outlet in the same house or building. Since the wall outlets in most houses are tied to the same ground, the ground is a common source of conducted interference, especially from the low frequency hum of an electric motor. Turn on both devices at the same time.   4. Is electromagnetic interference bad for you? There is no doubt that short-term exposure to very high levels of electromagnetic fields can be harmful to health. ... Despite extensive research, to date there is no evidence to conclude that exposure to low level electromagnetic fields is harmful to human health.   5. What are three types of interference? Electromagnetic interference (EMI) Co-channel interference (CCI), also known as crosstalk. Adjacent-channel interference (ACI) Intersymbol interference (ISI)   6. What material can block electromagnetic fields? Typical materials used for electromagnetic shielding include sheet metal, metal screen, and metal foam. Common sheet metals for shielding include copper, brass, nickel, silver, steel, and tin.   7. What blocks electromagnetic interference? Carbons. Carbon materials (e.g., coke, graphite, graphene, carbon fiber, carbon nanofiber and carbon nanotube) are not only conductive electrically, they are good absorbers of electromagnetic radiation over a wide frequency range.   8. Can humans cause electromagnetic interference? The human body functions as an antenna in the low-frequency band used by HBC. Owing to this antenna function, electromagnetic waves radiating from electronic devices or wireless services cause electromagnetic interference (EMI) in HBC devices.   9. What are two sources of electromagnetic interference that can affect data transmission? Electromagnetic interference can be categorized as follows: Narrowband EMI or RFI interference typically emanates from intended transmissions, such as radio and TV stations or mobile phones. Broadband EMI or RFI interference is unintentional radiation from sources such as electric power transmission lines.   10. What is the EMC? Electromagnetic Compatibility, also known as EMC, is the interaction of electrical and electronic equipment with its electromagnetic environment, and with other equipment. All electronic devices have the potential to emit electromagnetic fields. You May Also Like: Research on Space Monitoring and Location Technology of AR&VR Equipment Detailed Analysis of Flexible Electronics Materials and Applications Look Forward to the Future of Semiconductor  

There is no doubt that the use of LCD headlamp is a succcessful further step towards digitalizing lighting. LCD headlamp which enables complex functions will also be relevant to autonomous driving. Let's talk something about the following research project about developing a headlamp basics on a LCD (  Full name is Liquid Crystal Display )which made by HELLA and seceral partners.This technology is an good example already known in the home entertainment field.  About The ProjectIn the context of the research project funded by the Federal Ministry of Education and Research (BMBF) regarding the fully adaptive light distribution for intelligent, efficient and safe vehicle lighting (VoLiFa2020), HELLA has developed a headlamp on the basis of a Liquid Crystal Display (LCD) in collaboration with project partners Merck, Institut für Großflächige Mikroelektronik IGM, Stuttgart University, Porsche, Elmos Semiconductor, Schweizer Electronic, and the University of Paderborn. Complex FunctionsIn general,the new LCD headlamp projects 30.000 pixels onto the road. This allows adjusting the light pattern in an intelligent and continuous manner to various driving situations in real time. The use of an LC display is a further step towards digitalizing lighting. This means: the adaptation of the light pattern will increasingly be determined by software. The driver will obtain the best possible view of the road. Individual segments with e.g. other traffic participants or strongly reflecting street signs can be omitted or dimmed in a targeted manner. Highly complex functions are also conceivable: navigation arrows or lines showing the ideal lane can be projected onto the road. LCD technology enables functions that will also be relevant to autonomous driving.  The LC display is the headlamp’s key component. It is situated between the LED light source and the projection lens. The display generates a matrix with 100 x 300 pixels that can be individually controlled and dimmed. A camera installed in the vehicle as well as a sensor optically reading distances and speeds (light detection and ranging sensor, LiDAR), will forward the ambient information to the headlamp control unit via a processor. This will then direct the individual display pixels up to 60 times per second. 25 high-power LED’s arranged in three rows will serve as light source. Each LED’s light intensity will be adjusted to the respective lighting situation. Due to increasing traffic volumes and safety requirements, intelligent lighting systems are of increasing importance. LCD technology enables completely new functionalities and opportunities here. And the use is not limited to passenger cars. Other vehicle categories, such as commercial vehicles or buses also provide meaningful application areas. ThanksgivingThanks to this project's great resolution and sharpness of detail, it opens up a diffirent new paths in automotive lighting technology. 

LCD stands for “liquid crystal display” and technically, both LED and LCD TVs are liquid crystal displays. The basic technology is the same in that both television types have two layers of polarized glass through which the liquid crystals both block and pass light. So really, LED TVs are a subset of LCD TVs.LED, which stands for “light emitting diodes,” differs from general LCD TVs in that LCDs use fluorescent lights while LEDs use those light emitting diodes. Also, the placement of the lights on an LED TV can differ. The fluorescent lights in an LCD TV are always behind the screen. On an LED TV, the light emitting diodes can be placed either behind the screen or around its edges. The difference in lights and in lighting placement has generally meant that LED TVs can be thinner than LCDs, although this is starting to change. It has also meant that LED TVs run with greater energy efficiency and can provide a clearer, better picture than the general LCD TVs.Source: BY HOWSTUFFWORKS.COM CONTRIBUTORS