Video Hardware - Upgrading and Repairing PCs - page 823

CRT Display Technology
CRTtechnologyisthesameusedinoldertelevisionsets.Inthepastfewyears,CRTshave
vanishedstoreshelves,mainlyduetotheavailabilityoflower-costLCDs.However,many
older systems still use CRT monitors. CRTs consist of a vacuum tube enclosed in glass.
One end of the tube contains an electron gun assembly that projects three electron beams,
oneeachforthered,green,andbluephosphorsusedtocreatethecolorsyouseeonscreen;
the other end contains a screen with a phosphorous coating.
When heated, the electron gun emits a stream of high-speed electrons that are attracted to
theotherendofthetube.Alongtheway,afocuscontrolanddeflectioncoilsteerthebeam
to a specific point on the phosphorous screen. When struck by the beam, the phosphor
glows. This light is what you see when you watch TV or look at your computer screen.
Three layers of phosphors are used: red, green, and blue. A metal plate called a shadow
mask aligns the electron beams; it has slots or holes that divide the red, green, and blue
phosphors into groups of three (one of each color).
MonitorsbasedonSonyTrinitronorMitsubishiDiamondTronpicturetubesusedanaper-
ture grille type mask to separate red, green, and blue phosphors, resulting in strips of
square pixels in a linear arrangement, similar to an LCD. NEC's ChromaClear monitors
usedavariationontheaperturegrillecalledthe slotted mask ,whichisbrighterthanstand-
ardshadow-maskmonitorsandmoremechanically stablethanaperturegrille-basedmon-
itors. This resulted in a staggered pixel arrangement.
Varioustypesofshadowmasksaffectpicturequality,andthedistancebetweeneachgroup
of three (the dot or pixel pitch ) affects picture sharpness.
See “ Pixels ,” p. 643 (this chapter).
Figure 12.23 illustrates the interior of a typical CRT.
Figure 12.23 A typical CRT monitor is a large vacuum tube. It contains three electron guns (red, green,
and blue) that project the picture toward the front glass of the monitor. High voltage produces the magnet-
ism that controls the electron beams that create the picture displayed on the front of the CRT.