Sourcing Low Power Consumption Displays

With the trend toward more connected devices and the drive to smart watches, small displays that consume little power are becoming critical for more and more applications. When it comes to electronic products, the display is among the 2 or 3 most power hungry components.

Our engineering team wrote this overview of available technologies, to help buyers compare the right types of display.

The first step to identify the most suitable technology is to understand the application requirements in terms of:

• Display size
• Resolution – number of dots or pixels
• Power consumption when display is on
• Contrast – difference between white and black colors
• Luminosity – ability to see details under the sun for example
• Visual angle – does it also look nice from the sides?
• Graphic or segment: Segment is particularly suitable for simple applications (especially those using icons or pictograms), while Graphic is pixel based and offers unlimited display.

The technologies that can be found on the market can be classified in 4 families:

1. TN: Basic liquid crystal concept with many variants such as HTN, FTN, STN, FSTN… Each variant has an advantage on visual angle, power consumption, color, and resolution. While the visual aspect is poor compared to classic smartphones, they bring great value in term of cost and power consumption. It means they are the perfect choice for low cost applications.

2. TFT LCD (also called active LCD): This is the major technology for mobile phone displays. Its strengths are great colors and high resolution thanks to a transistor matrix (TFT) integrated with liquid crystal. Its major downside is the need for backlight, which increases power consumption.

3. OLED: This is a more recent technology. The advantage of OLED is that each dot can generate its own light, meaning that black dots don’t need power. Its power consumption is much better optimized than with TFT LCD. The unit cost being higher, it is more common on high-end phones. An OLED display can also be fitted on a flexible support, which allows a wider range of applications.

4. EPD (also called electronic paper): This is the most recent solution based on electronic ink. Since it consumes no power on a static page, it is perfect for e-book reading devices. it is based on ink, so the light cannot come from the display. It offers very high visual quality in luminous environments thanks to very high contrast. Like OLED, EPD can also be fitted on a flexible support, but color is still a challenge.

The table below summarizes the main differences between the families of technologies:

On top of the criteria listed above, the selection of the right display should also take into account what already exists on the market. Customized versions are costly — they require a mold or tool that might represent up to a 1 Million USD investment.

Finally, most displays come with a driver to adapt its interface to your device. Drivers can be a burden in the selection process. They can have a short lifetime, limited features, or be very costly.

There are hundreds of Chinese suppliers, from the very low to the high end. The information available on the Internet is limited and can lead to a wrong strategic decision – switching to another display supplier after the first prototypes takes a long time and is costly.

Here is the typical information you need to ask potential suppliers:

• What part of the display are you responsible for? (Many manufacturers only do final assembly.)
• Is your business growing? If it is stable, what are the reasons?
• Why are your costs lower than the competition? (Working with a supplier that makes a low margin is only good for the short term.)