Liquid-crystal display (LCD) has become one of the world’s most popular display technologies. While the technology has been around for over a century — yes, LCD is really that old — it wasn’t until the turn of the 21st century when LCDs were able to offer a high-quality, reliable display experience. Today, LCDs are used in countless display applications, including mobile devices, human machine interfaces (HMIs), computer monitors, video game consoles and more.
While all LCDs contain liquid crystals which are illuminated with a backlight, there are different types of LCDs, including passive- and active-matrix. If you’re thinking about purchasing an LCD, you should familiarize yourself with these two common types. Passive-matrix LCDs may look like their active-matrix counterpart, but they are two unique technologies that operate in different ways.
Passive-Matrix LCDs Explained
Passive-matrix LCDs are characterized by a grid-like arrangement of conductors, which are usually made of a conductive material like Indium Tin Oxide (ITO). Of course, ITO looks like transparent glass. Unlike conventional glass, though, it’s highly conductive, allowing electricity to travel through it. These two properties make ITO an incredibly useful material for use in passive-matrix LCDs.
In a typical passive-matrix LCD, pixels are controlled at the junction where the ITO conductors meet. Voltage can be increased or decreased at the intersecting junctions, allowing for the creation of images.
Passive-matrix is one of the oldest types of LCD technologies, with origins dating back to the early 1980s when super-twisted nematic STN was pioneered by the Brown Boveri Research Center.
Active-Matrix LCDs Explained
Active-matrix LCDs, on the other hand, feature a back panel made of silicon. Why does this matter? Well, instead of ITO, passive-matrix LCDs use silicon, which allows for the creation of a transistor for every pixel. As a result, they are able to produce better images with a higher contrast, lower response time and improved viewing angle. Active-matrix LCDs typically cost more than their passive-matrix LCDs, but many consumers and business owners will agree that active-matrix LCDs are well worth the investment.
It’s important to note that there are several types of active-matrix technologies, some of which include the following:
- Twisted nematic (TN): contains liquid crystals that automatically twist in various direction to allow or restrict the passage of light.
- In-plane switching (IPS): uses an electrical switch to align liquid crystal with the glass layer.
- Super in-plane switching (SIPS): similar to IPS except it’s able to deliver brighter colors and shorter response times.