Pixels on different display technologies
LCDs with high resolutions, such as large-screen LCD televisions, require an active-matrix structure.
The electrodes on one side of the LCD are arranged in columns, while on the other side they are arranged in rows, forming a large matrix that controls every pixel. Each pixel is designated a unique row–column combination, and the pixel can be accessed by the control circuits using this combination. These circuits send charge down the appropriate row and column, effectively applying a voltage across the electrodes at a given pixel.
Simple LCDs such as those on digital watches can operate on what is called a passive–matrix structure, in which each pixel is addressed one at a time. This results in extremely slow response times and poor voltage control. A voltage applied to one pixel can cause the liquid crystals at surrounding pixels to untwist undesirably, resulting in fuzziness and poor contrast in this area of the image. LCDs with high resolutions, such as large–screen LCD televisions, require an active–matrix structure.
This structure is a matrix of thin–film transistors, each corresponding to one pixel on the display. The switching ability of the transistors allows each pixel to be accessed individually and precisely, without affecting nearby pixels. Each transistor also acts as a capacitor while leaking very little current, so it can effectively store the charge while the display is being refreshed.