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EET 450 – Advanced Digital

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

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EET 450 – Advanced Digital

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  1. EET 450 – Advanced Digital Video Display Systems

  2. 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

  3. 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

  4. CRT

  5. 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

  6. 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

  7. 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

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

  9. 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

  10. 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

  11. Image distortion • Distortion can be caused by maladjustment of the electronics

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

  13. 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

  14. 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.

  15. 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

  16. 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

  17. LCD’s

  18. 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.

  19. 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.

  20. Other Flat panel technologies • DSTN

  21. Other Flat panel technologies • Field Emission display

  22. Other Flat panel technologies • Electro-Luminescent display – LED

  23. Other Flat panel technologies • Gas Plasma (currently winning)

  24. Other Flat panel technologies • Thin CRT

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

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

  27. Other physical connections • BNC • Enhanced Video Connector

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