EET 450 – Advanced Digital Video Display Systems

Video Display - CRT Video displays convert the digital information stored in memory to some form of visible display Originally, the Cathode Ray Tube was used Electrons were ‘boiled’ off of a plate, then accelerated to strike a plate covered in an phosphor The phosphor glows due to the energy of the electron

CRT By controlling the position on the screen, and the intensity of the dot, intelligible information can be displayed. The CRT is a glass encapsulated array of electrodes Contained in a vacuum RASTOR display versus VECTOR display

CRT

The Electron gun is the cathode part of the display Electrons are boiled off a beryllium plate The electrons are accelerated by an electric potential with plates in the neck The cloud of electrons is shaped into a beam The electrons in the beam are accelerated by the attraction to the face (anode) of the CRT

CRT As the electron beam passes through the funnel on the way to the face, it is deflected A raster display, sweeps from left to right/ top to bottom of the display As the face is ‘painted’ by the electron beam, the intensity of the beam is varied by control plates in the neck. At the face, the phosphor is struck by the electron beam

CRT The color of the spot of phosphor depends on which rare earth element is used in the phosphor Monochrome CRT’s use a single phosphor Color CRT’s use 3 primary colors of phosphors to obtain the RED, GREEN and BLUE The additive color blending scheme allows any color to be made from RGB combinations

CRT Face The phosphor is applied to the face in a variety of patterns. aperture shadow slot grill mask mask

CRT Face The electron beam is further shaped by a metal ‘mask’ that allows the beam to strike only specific areas of the face ‘Dot Pitch’ is the distance (in mm) from one group of dots to another

CRT Characteristics The shape of the face has much to do with distortions Screen curvature Resolution Vertical versus horizontal dots Anti-glare treatment Screen size Aspect Ratio

Image distortion Distortion can be caused by maladjustment of the electronics

Image distortion The beam must be adjusted to correctly strike the groups of phosphors which make up a pixel Purity Linearity adjustment

Display Characteristics Interlacing Each sweep of the face paints alternately even/odd lines Keeps the required bandwidth down Non-interlaced displays are standard now Each line is painted, every sweep See table 17.3 for bandwidths of standard video displays

Display characteristics The vertical sweep is dependent on ‘sync’ frequency Most monitors are now ‘multi-sync’ or multi frequency TV’s are at a rate of 30 frames per second CRTs for computers range from 30 to 80+ per second.

Other features Energy Star Low power requirements Sleep mode Monitor off (see the discussion from ‘power supply lecture on ‘green’ requirements.) Plug and Play CRT’s now comply with PNP standard

Flat Panel Systems LCD – Nematic technology Supertwist, double supertwist, etc. Light is passed through a ‘liquid crystal’ Polarization of light Dependent on electrical field Passing light through a static polarizing filter, then through ‘spot’ of varying polarization, gives light/dark

LCD’s

‘Spots’ of screen are passed through colored filters to provide RGB components The eye blends spots into single colors. Alternative to Nematic technology LCD’s is Cholesteric Technology Bi-stable – thus more energy efficient.

LCD’s Passive matrix Control voltages are applied at edges of LCD panel Heat dissipation and contrast are a problem Active Matrix Transistors are embedded in the display panel. Power is applied to transistor, which amplifies contrast.

Other Flat panel technologies DSTN

Other Flat panel technologies Field Emission display

Other Flat panel technologies Electro-Luminescent display – LED

Other Flat panel technologies Gas Plasma (currently winning)

Other Flat panel technologies Thin CRT

Other Display Units Projection units Overhead display panels VR Goggles 3D glasses

Connectors CRT connectors are now standard at 15 pin high-density D-shell connector Replaces 9 pin D connector

Other physical connections BNC Enhanced Video Connector