From COG to LCM: Understanding the abbreviations in touch screens

If you are new to the touch display industry, you will definitely be confused by various abbreviations. COG, FOG, TPM, LCM... look like passwords, which are often confusing for people who are new to this field or external customers. Today we will talk about them one by one to help you sort out the "jargon" that is often mentioned in the touch display industry.

First of all, this is the LCD Panel, also called liquid crystal glass, which is the core basic material of the entire display module. As the name suggests, its function is to display the picture, but it has no driving function and will not emit light by itself. It is like a "brain without electricity" and is only responsible for the arrangement of liquid crystal molecules to control light transmission.

At this time, we will add an IC, that is, a driver chip, to the panel. At this time, it becomes COG. The full name of COG is Chip On Glass, which means "mounting the chip directly on the glass". This packaging method is widely used in small-size modules, such as vehicle-mounted instruments, bracelet screens, industrial control screens, etc. Its advantages are small size and fast response, which is suitable for devices with compact space.

So, COG is a combination of panel and driver IC. It can convert data into electrical signals through chips, drive the liquid crystal arrangement, and make the screen really "light up".

Next is this one, called FPC, which means flexible circuit board. You can think of it as a soft cable, which is responsible for connecting the signal and power supply on the COG to the motherboard, and is the bridge between the entire module and the system. FPC usually also integrates some electronic components, such as capacitors and resistors, and sometimes touch chips are soldered on it.

When FPC and COG are combined, it becomes FOG. The full name of FOG is Film On Glass. Although it literally means "film on glass", it is often used in the industry to mean "COG with FPC". It can be understood as having one more interface than COG, and customers can directly connect it to the motherboard after taking it home.

So far, this structure cannot emit light, because the LCD panel needs a backlight. At this time, we have to introduce BL, which is the backlight module. The backlight is equivalent to the light source of the LCD. Without it, no image can be seen. Common backlight structures include direct-down and side-in. The common color is white light, and a few industrial fields also use yellow light or red light.

So, when we assemble FOG and backlight module together, it becomes LCM. The full name of LCM is Liquid Crystal Module, which is called liquid crystal display module in Chinese. It contains glass, IC, cable and backlight, and is a display component that can truly "display the picture". As long as it is powered, the image can be displayed. When customers purchase, they often ask "what size LCM do I want" and "what is the resolution", which refers to this.

Next, we go one layer further out. This is TP, or Touch Panel. The layer of glass that you can touch, swipe, and slide with your finger is TP. It is responsible for identifying the movements of your finger and transmitting the coordinates to the main control chip. There are many types of TP structures, such as G+G (glass cover plus glass sensing layer), G+F (glass cover plus thin film sensing layer), etc. Different structures determine the touch feel, thickness, and cost.

The last step is to stick TP and LCM together and assemble them into a whole through the bonding process, and it becomes TPM. TPM means Touch Panel Module, also known as touch display module. It integrates display and touch functions and is used in mobile phones, car machines, electric car instruments, coffee machines, medical equipment and other terminals that require interaction. To sum up, the structural order from inside to outside is as follows: LCD panel is the most basic display glass. After adding the driver chip, it is called COG. After adding the cable, it is called FOG. After adding the backlight, it becomes LCM. After attaching the touch, it becomes TPM. These abbreviations sound complicated, but in fact, each step is an upgrade of structure and function. As long as you understand this order, when you hear COG, FOG, LCM, TPM in the future, you will not only remember the letters, but also truly understand their structural meanings.