What does active matrix mean ?

Essentially, passive Matrix LCD monitors are made by putting a layer of liquid crystal dots over a cross-crossing grid of wires backed by a fluorescent backlight. In a Passive Matrix display, current is applied to the wire intersections.

The current causes the liquid crystal dots at that point to untwist (turn on) and allow light to pass through.

The image that occurs is maintained by applying the current to the intersections at a set refresh rate and depends upon the ability of the liquid crystal to stay untwisted between refreshes.

Passive Matrix LCD displays have slow response times and tend to display fuzzy images that lack good contrast and brightness.

Active Matrix LCD monitors, in contrast, have a cross-crossing matrix of thin film transistors (TFT) instead of a matrix of wires. TFTs are basically very small, very thin transistors and capacitors.

In an Active Matrix LCD monitor, the current is applied to the capacitors located at the row and column intersections.

The current at the intersection causes the liquid crystal to untwist and the capacitor retains the charge, actively keeping the crystal untwisted, until the next refresh cycle. The transistors control the amount of current going to the liquid crystal and the capacitor, thereby actively controlling the amount of untwisting.

Active Matrix LCD displays have much faster response times, clearer, brighter images, and much greater contrast than Passive Matrix displays.