EET 450 – Advanced Digital

Video Display Systems

Video Display - CRT

Video displays convert the digital information stored in memory to some form of visible displayOriginally, the Cathode Ray Tube was used

Electrons were ‘boiled’ off of a plate, then accelerated to strike a plate covered in an phosphorThe 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

CRT

The Electron gun is the cathode part of the display

Electrons are boiled off a beryllium plateThe 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 displayAs 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 FaceThe 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

ResolutionVertical versus horizontal dots

Anti-glare treatmentScreen sizeAspect 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

InterlacingEach sweep of the face paints alternately even/odd lines

• Keeps the required bandwidth down

Non-interlaced displays are standard nowEach 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 StarLow power requirements

Sleep mode

Monitor off (see the discussion from ‘power supply lecture on ‘green’ requirements.)

Plug and PlayCRT’s now comply with PNP standard

Flat Panel Systems

LCD – Nematic technologySupertwist, 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

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 matrixControl voltages are applied at edges of LCD panel

Heat dissipation and contrast are a problem

Active MatrixTransistors 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