How TFT Display Works
In this article, we’ll be covering how TFT displays work, the main differences between TFT and LCD, their typical display specifications and also outline a list of common applications where TFT displays are used.
If you’ve ever purchased a computer monitor or a television, then you’ll likely have heard of the terms TFT and LCD. They stand for thin-film-transistor and liquid-crystal display respectively and are the most common display technologies used in not just monitors and televisions, but also in cameras, GPS devices, tablets, medical equipment and even aircraft computers.
TFT vs. LCD
TFT and LCD are two commonly-used terms when describing display monitors, but they do have significant differences and thus different use cases:
- Uses a passive pixel matrix
- Does not always require the use of a backlight
- Can be used as a mono-colour display
- Great for simple display needs
- Very power efficient
- Poor response time, not ideal for moving pictures
- Suffers from crosstalk interference
- TFT technology is applied to LCD panels
- Uses an active pixel matrix
- Requires the use of a backlight to serve its function
- Almost always a colour display
- Great for displays that require smooth motion
- Sharp and vibrant colours
- Not as power efficient as LCD
How TFT Display Works
To understand how TFT displays work, it’s important to explain LCD technology first due to the way they both interact with each other.
An LCD uses liquid crystals to manipulate light. The molecules that make up the crystals twist depending on their temperature which is altered by using an electrical current. Depending on the rotation of the molecules, they can block the light in various ways to allow different colours to show on the screen or no light at all.
Groups of these molecules form a pixel, a word invented from the term “picture element”. It’s a unit of programmable colour on an LCD display that varies in size depending on a number of conditions, such as the current resolution of the display. Pixels contain red, green and blue colour filters and the molecules are twisted to release a certain amount of each light to create millions of different colour combinations.
Early LCD displays used a matrix of pixels known as passive matrix. This means that each individual pixel is controlled by sending an electrical charge to the row and column that it’s found in. Unfortunately, images on LCD displays were often blurry when the pixels needed to be switched often, such as during high-action scenes, due to the limited number of electrical charges that could be sent in a single second. In addition, the electrical charge would often interfere with adjacent pixels, causing a defect known as crosstalk.
In contrast, LCD displays today use an active matrix of pixels which contains a sheet of thin-film transistors. Each pixel in an active matrix is paired with a transistor that includes capacitors that give each subpixel the ability to retain their charge instead of requiring an electrical charge sent each time it needed to be changed. This means that TFT displays are more responsive than regular LCD monitors. TFT displays are often called TFT-LCD monitors because the two technologies are used together to produce a clear and non-blurry image.
Due to the use of an active matrix of pixels, TFT displays have faster response times which means clearer pictures and less blurring, and also provide more vibrant colours that can be controlled with precision thanks to the thin-film transistors.
Application of TFT Displays
TFT displays can be used in a number of consumer, commercial, industrial and automotive products.
Picture quality, sharpness and responsiveness are all important for a good television so a panel with high resolution, brightness and physical size would make the ideal display panel. On the other hand, vehicles may want displays with higher brightness in order to work in conditions with more sunlight. These panels also tend to have wider operating temperatures to ensure that the surrounding equipment does not affect the quality of the screen.
TFT Display Specifications
TFT displays from GSR Technology come in various different designs and specifications. Here is a list of specifications that are typically listed and their definitions:
- Size or format is used to describe the physical distance between opposite corners of a display, usually expressed in inches and often referred to as the physical image size.
- Resolution refers to the number of pixels in each dimension (width and height) that can be displayed by the panel.
Refreshrate is expressed in Hertz and is often included at the end of the resolution specification. Commonly referred to as vertical refresh rate, it is used to measure the number of times a second that the display can update its buffer. Normal displays operate at 60 Hz.
- Brightness or luminance is a measurement of luminance and is expressed in nits. Between 200 and 300 nits is where an average display sits, whereas 700 nits offer far greater contrast, resulting in sharper picture quality.
signal or interface describes the input types available on the display. Input
- Monitor dimension refers to the physical size of the monitor and is expressed in width, height and depth.
- SVGA: 800 x 600, 4:3
- XGA: 1024 x 768, 4:3
- WXGA: 1280 x 720, 16:9
- HD: 1366 x 1768, 16:9
- HD+: 1600 x 900, 16:9
- FHD: 1920 x 1080
Another factor in TFT displays is the range of operating temperatures it can cope with. This is especially important in industrial and automotive uses where equipment surrounding the TFT display can affect the picture quality. Since heat from electrical currents is used to change the orientation of the molecules in each subpixel, outside heat sources can turn the liquid crystals inside a TFT-LCD display into a real liquid due to their sensitivity to temperature changes.