EMI Compliance Test

What is EMI?

With more people using electronic devices like cell phones and computers, there is a higher density of electromagnetic currents in the environment. As more and more electronic devices get developed and used, the impact of EMI continues to grow. You may have heard about EMI before and wondered exactly what they were. Although we cannot see or feel EMI, it can be detected and measured with instruments. And that's why the International Special Committee on Radio Interference (CISPR) set up the technical publications covering measurement and recommended emission limits to deal with the emerging problem of EMI.

EMI: Electromagnetic Interference 

Electromagnetic interference (EMI) is a phenomenon that may occur when an electronic device is exposed to an electromagnetic (EM) field. It affects an electrical circuit and electronic malfunctions.

Types of EMI (Electromagnetic Interference)

Electromagnetic Interference can arise in many ways and from different sources. Typically, there are two types of EMIs: Naturally occurring EMI and Man-made EMI.

✦ Man-made EMI

This type of EMI occur as a result of the activities of other electronic devices in the vicinity of the device (Receiver) experiencing the interference, such as cellular networks, television transmissions, radio and satellite. Some industrial and medical equipment causes of EMI affect technologies within the same facility or process, while others like grid power interruptions that can cause more widespread disruptions.

✦ Naturally occurring EMI

It is caused by natural sources of EMI, such as lightning, rain spray, solar radiation, electrical storms, cosmic noises and other atmospheric types of noise occurrences. 

✦ Other Sources

It is also possible to categorize the different types of EMI by their bandwidth, transmission routes and other external sources.

The Effect of EMI on Electronic Devices

We live in a digital world with all sorts of electronics around us. However, we cannot ensure whether our devices pass such as EMI compliance test or not. Moreover, it may cause unnecessary disturbance for engineering design and even postpone the development processes. As the demands for reduced electromagnetic noise and other disturbances increase, many of the EVERVISION TFT modules have undergone EMI compliance self-tests. By offering EMI-compliant products, EVERVISION aims to shorten product development time for our clients and continues to provide products with quality, safety compliance, and stability.

Electromagnetic Interference (EMI) Compliance Standards 

It is important to carry out EMI analysis in the design phase of an electronic product to predict the radiated emissions. Most products have to pass some sort of conducted emissions tests so that the designer can minimize and eliminate EMI before it becomes a problem. Besides, with regard to EMI compliance standards, there are some differences between countries and regions. Therefore, all electronics needs to be substantiated and tested before selling. To shorten product development time, EVERVISION TFT LCD modules have undergone EMI compliance self-tests with CISPR-based emission limits.

EMI Effects on The Performance of Electronic Circuit

Depending on the severity of the disruption, EMI may impact the quality of the signal the device receives, cause a component to fail or malfunction temporarily or permanently damage the electronic devices. There are several ways to reduce noise in an electrical circuit and one of the most effective methods is undergoing EMI testing.

Measurement and Analysis

For the baseline measurement, radiated emission of TFT LCD module was measured in 3m semi-anechoic chamber.

Test Equipment Setup 

Electrical Measuring Instruments  

EMI Testing Procedure

First, connect source (Laptop) to TFT display module (Support HDMI Signal) with HDMI cable. Then, connect the USB cable to a USB port on the computer. Besides, a stable voltage is required by analog circuits because of its sensitiveness to noise. Make sure the TFT display module was plugged into the power using 12V DC adaptor before testing.

Figure 2 : The Block Diagram of Test Setup 

EMI Test on TFT LCD Module

For the baseline measurement, radiated emission was measured in 3m semi-anechoic chamber. The measurement was performed with vertical and horizontal polarization of the receiver antenna. And, the test image of display is based on CE standard: EMC Color Bar Pattern

EMI test result in datasheet​ : Model VGG128004-Q

According to CISPR 32, the limit is 40 dBuV/m from 30-230 MHz and 47 dBuV/m from 230-1000 MHz when making measurements at 3 meters for class B residential environment. Figure below shows the radiated emission limits of TFT display module with vertical and horizontal polarization in EMI test report. The radiation pattern allows us to determine the direction of maximum radiation for a given frequency.

Passing EMI Compliance Self-Tests for TFT Display Module

As the demands for reduced electromagnetic noise and other disturbances increase, many of the EVERVISION TFT modules have undergone EMI compliance self-tests and performed well at specified EMI limits (30-230 MHz: limit 40 dBuV/m, 230-1000 MHz: limit 47 dBuV/m). 

EMI limit : 30-230 MHz, limit 40 dBuV/m, 230-1000 MHz, limit 47 dBuV/m

EVERVISION TFT display modules that are outlined in the table (Related Products) below passing the EMI compliance self tests.

※ We will keep launching more sizes of TFT display modules with EMI compliance test.