Signals and Connectors
Another major difference between CRT and LCD displays is that a CRT is an analog
device that uses an electrical wave to create the display, and an LCD is a digital device.
CRTs, even those with a digital connection, must convert the PC’s digital signal into an
analog signal. This is done either on the video card or in the monitor by a device called a
digital-to-analog converter (DAC). The video card sends the digital information gener-
ated by an application program to its DAC, which converts the signal into an analog
wave and sends it over the connecting cable to the monitor. Even if the CRT has a digital
interface, the signal must still be converted to analog.
A flat-panel LCD monitor connected to a standard DAC video card must reprocess the
analog signal through its analog-to-digital converter (ADC), which can lead to image deg-
radation. Analog and digital flat-panel monitors are available. If you wish to use a digital
flat-panelLCDmonitor,makesureyourvideocardiscapableofproducingdigitaloutput.Monitor Controls
Most CRT style monitors have a control panel on the front or side that allow you to adjust
thebrightness,contrast,focus,andscreensizeorshape.Someuseseparateknobsforeach
feature that can be adjusted, and others use a single control knob or wheel. Virtually all
new monitors, whether LCD and CRT, have onscreen displays (OSD) that allow you to
see exactly what adjustment you are making and its effect on the display. Focus controls
on a CRT really adjust the convergence of the electron beams on each pixel. As is discussed
in more detail later, each pixel has three electron beams (one for each phosphor dot) that
can become misconverged, which is a techie way of saying out of alignment.
Misconverged beams cause a blurry or fuzzy image.
The CRT’s size and shape adjustments are used to fix barreling (when the sides of the
display bow outward), pin-cushioning (when the sides bow inward), and rotation (when
the top or bottom of the display is not level).
Although they do not have misconvergence problems, LCD panel monitors can have
displayandfocusproblems.Aflat-panelmonitorhasadjustmentstosynchronizeittothe
video card. LCD monitors are set to standard VGA timings at the factory, and a particular
PC and video card may use a slightly different timing. This can result in a distorted or
blurry display. To correct this, the monitor has adjustments for its Frequency/Clock and
Focus/Phase settings.Video Display Standards
Videodisplaystandardsaredevelopedmoretodefinethecapabilitiesofvideocardsthan
they are for monitors, but by listing the video standards to which the monitor is compatible,
its capabilities in terms of color depth and resolution are automatically defined.
What differentiates one video display standard from another is the resolutions it
supports, how itcreates text characters, whether it is color or monochrome, and its color
depth, color palette, refresh rate, scan rates, and bandwidth. Table 16-5 lists the resolutions(^378) PC Hardware: A Beginner’s Guide