Solution to Electromagnetic Interference of TFT LCD LCD Screen

Electromagnetic interference has always been a headache for the overall system operation of products. When subjected to electromagnetic interference, interference waves of certain frequency and amplitude are generated on the power or signal line, which affects the normal operation of the entire machine product and is reflected through the LCD display screen.

As we all know, TFT LCD module is a passive output module. It only receives input signals and has no judgment. Therefore, incorrect signals and data will generate incorrect control instructions, leading to incorrect display effects and patterns. So how to solve the problem of electromagnetic interference of the LCD module ? The first task is to find the source of interference and use the most effective methods to eliminate, weaken, prevent and shield it. Below, we will analyze the several situations in which TFT LCD screens are affected by electromagnetic interference, as well as their solutions.

I. White/blue screen on the LCD

During LCD module operation, a white/blue screen may appear. This refers to the LCD module only having backlight on and not responding to contrast adjustments. This is because during the product's operation period, electromagnetic interference is applied to the VDD or VSS of the LCD screen module or the RESET signal line, which results in the LCD screen module being reset. The result of this reset is that the module's internal register is initialized, and the display module is turned off.

Solution: If the interference is applied to the power line, a stable capacitor and a filtering capacitor should be added between the VDD and VSS of the power line closest to the LCD display module. If the interference is applied to the RESET signal line, a filtering capacitor should be added between the RESET signal line and VSS closest to the LCD display screen. The capacitance should be selected based on the actual test results.

II. Incorrect characters or data appearing on the LCD screen

During product operation, the LCD screen may display incorrect characters or dots (data error), which cannot be restored and can only be reinitialized by power-on. This is because electromagnetic interference is applied to the control signal, causing changes in the register parameters. Generally, the operation is to write display data, rather than repeatedly writing the main working register parameters, which can result in the above phenomenon.

Solution: If the interference is applied to the transmission line between the MPU and the LCD screen, the following methods can be used: (1) shield the circuit with a magnetic ring or tin foil; (2) change the direction of the transmission line to avoid interference environment; (3) shorten the length of the transmission line, or add a transmission line driver to improve the driving and anti-interference ability. The actual test results should be observed to determine whether the display effect is improved.

There is also a case where interference comes from the product's mainboard, and the LCD screen displays incorrect characters. The reason may be that the resistance between the MPU and the LCD screen transmission line is too high, causing the interference signal to easily invade the line. The solution is to connect a small resistor in series on the transmission line and a low-pass filter circuit composed of the input capacitor at the display module end to eliminate the interference effect.

III. Electrostatic Interference on LCD Screens

Because of electrostatic interference from the housing of the LCD module, especially the glass panel, the LCD screen may experience white screen or erratic display. This interference is mainly caused by the iron frame or glass panel of the LCD module interfering with its circuits. To solve this problem: (1) ground the iron frame of the LCD module; (2) connect the iron frame of the LCD module to VSS or leave it floating; (3) insert an insulating pad between the iron frame of the LCD module and the metal housing. The thicker the insulating pad, the greater the reduction of electrostatic interference. These three methods can be selected during testing to observe improvements in display performance.

IV. White or Erratic Display without External Interference Sources

This situation also falls under interference, which is caused by internal interference in the system, mainly due to program conflicts in software. First, determine the pattern of interference. If it occurs during the writing process of the module, it may cause the module to freeze or display errors. In this case, interrupt programs should be considered. Interrupt programs can cause errors such as the modification of control signals or data during the process of MPU writing to the LCD screen, resulting in module crashes or display errors. The solution here is to disable interrupt response during MPU invocation of the LCD screen driver program.

Various scenarios of electromagnetic interference on TFT LCD screens have been analyzed, and their solutions have been presented. Therefore, it is important to first locate the problem, conduct targeted testing, and observe any improvements in the display performance of the LCD screen. Of course, there are many other instances of electromagnetic interference, which require experienced engineers to analyze and test.