(^392) PC Hardware: A Beginner’s Guide
flat-panel monitors, incorporates back lighting elements. Most computer displays are
lightedwithbuilt-influorescenttubesaroundtheedgesandsometimesbehindtheLCD.
LCD Types
There are three different types of LCD used in various devices: common-plane, passive
matrix, and active matrix.Common-Plane LCD
Common-plane LCD is not used for PC displays, but it is the type used on watches,
handheld games, and microwaves. This is essentially the type of display discussed above
that is very good for displaying the same information repeatedly.Passive Matrix LCD
A passive matrix LCD uses pixels instead of electrodes, but the principles are the same as
used in the common-plane LCD. A grid organized in rows is used to energize the pixels.
Integratedcircuitscontroltherowsandcolumnstoensurethatachargesentoverthegrid
gets to the specific pixel it was intended to activate.
The rows and columns of the grid are created on separate layers of a transparent conduc-
tive substrate, typically indium tin oxide. A layer of liquid crystal is sandwiched between the
twosubstrates,andalayerofpolarizingfilmisaddedtothetopandbottomofthesandwich.
A pixel is energized when the integrated circuit sends an electrical charge down the
appropriate column (on one of the substrates) and a grounding charge over the appropriate
row (on the other substrate). The two charges converge at the pixel located at the intersec-
tion of the row and column. The charge untwists the liquid crystals of the pixel and the
area darkens.Figure 16-14. Examples of number displayed on an LCD