Electronics - LCD Screens

LCD is the acronym of Liquid Crystal Display. There are two types of LCDs – Passive Matrix LCDs and Active Matrix LCDs. In passive type of LCDs the screen is divided in to a large no of small portions / cells – Liquid Crystal Cell. A white source of light is placed at the back of the screen then the LCC is charged / activated by a conductor grid. Then it will change the chemical property so that its ‘light conductivity’ will also vary.

Depending on the light absorption property of that pixel the display on the front screen will also vary. In effect a passive type LCD screen will modifies the white background light source to a picture by blocking / absorbing some light which is the function of picture in the front screen. Even if the technology and manufacturing of the screen is simple, the electronic driver design is difficult because each pixel here to be precisely exited and its voltage have to be maintained. It makes the circuit more complicated and bulky.
In active matrix LCD display base technology used is Tin Film Transistor (TFT). As in the passive LCD it is also have a large no of cells / pixels. Each cell / pixel contains a thin film transistor and a capacitor and it can be activated or address by row and column mechanism. Here the capacitor is charged once and it holds the charge until the next refresh. So even after the removal of supply voltage the information is maintained.
So here each pixel hardware can be reused.. However single pixel LCDs can not produce different colours I,e these are monochromatic in nature. To get different colours we have to use colour filters. TFT type LCD modules are lighter, smaller, faster and less power consuming compared to other common displays.