Ed's AV Handbook.com
Home Theater & High Fidelity Stereo Audio


Chapter Four
Video Reproduction

Page 5

Batting practice for the audio/video pro and a primer for the novice
 


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THE TV
            LCD TV dominates the retail floor.  OLED TV has emerged as the high performance
TV choice.  
DLP and LYCOS/DILA are still the popular video projector options.   The CRT and plasma TV are history but still relevant to understanding 'The  TV'.  And this page outlines each of these television technologies.

Cathode Ray Tube (CRT)
          The cathode ray tube was the technology that launched TV and dominated the 20th century.  Its key components included the cathode, the anode, two electromagnets, a steering circuit, a shadow mask, and 
vertical sets of red, green, and blue phosphor stripes.

          Somewhat as a light bulb filament, three heated filaments in the cathode created three distinct negative charged electrical currents.  The positive charged anode drew streams of electron beams from each negative charged cathode filament.  The combined cathode and anode was essentially an electron gun.  Each of the three streams emmiting from the gun was assigned to a primary video color signal.  
          The three streams were converged into a tight (but still separate) bundle that struck the
center of the shadow mask located behind and adjacent to the front screen.  Two separate   electromagnetic coils encircled the three beams.  The first coil shifted the electron beams vertically up and down.  The second coil sweeped the beams horizontally left to right.  
An electronic steering circuit, directed by the horizontal and vertical synchronizing signals, controlled the two coils.
         
Guided by the magnetic coils, the three modulating electron beams navigated the shadow mask from left to right, top to bottom, as they illuminated the red, green, & blue vertical stripes of phosphor located behind the mask.  The shadow mask (a fine wire mesh with a pattern of about 482 rows by 720 holes per row) allowed illuminated  phosphorescent
light to pass as a framed array of pixels on the TV screen that recreated the video image.        
                          

Rear Projection CRT TV
          A rear projection CRT TV consisted of three small CRTs mounted at the bottom of a large enclosure.  They were generally about 5 to 7 inches in diameter.  Each had a dedicated red, green, or blue phosphor layer.  Each CRT was coupled to an assembly of magnifying lenses.
        Each CRT assembly was matched to a primary color voltage. The three magnified assemblies were aimed and converged at a large first surface mirror at the rear of the enclosure.  The mirror reflected and redirected the magnified light through three front mounted translucent screens.

The three screens were the
Fresnel 
( fra-nell) lens, the Lenticular lens, and a protective screen.  The Fresnel lens redirected the light perpendicularly from its surface.  The lenticular lens redistributed the light laterally.  The third screen protected the Fresnel and lenticular lenses from dust and scratches.

Plasma TV
          A plasma TV is a mosaic matrix array of neon and zeon gas filled glass cells.
Each cells is coated with red, green, or blue phosphor.  
The TV digital controller applies voltage to each cell as dictated by the video signal line by line, pixel by pixel.  The electrically ionized gas in each cell emits ultraviolet light which illuminates the red, green, or blue phosphor in its cell.  The array of illuminated cells recreates the original light and picture.

LCD TV
            An LCD TV is a back lit mosaic array of red, green, or blue color filtered liquid crystal pixels.  Each pixel is a string of crystals suspended in liquid.  A front crystal anchors the string.  The next crystal in the string lays slightly off axis yet parallel to the front crystal.  Each successive crystal in the string (in a domino-like descending order) is slightly more off axis.  
           The mosaic array of crystals is sandwiched between a front and rear electrode glass plate.  The rear plate holds and aligns a vertical and horizontal matrix array of electrical conducting points behind each crystal.  
           Each set of back to back crystals allows polarized light to pass until the string begins to unwind and block the rear sourced polarized light. The unwind is controlled by the
electrical conducting points behind each LCD pixel string.  The degree of the unwind and passing light is adjusted by the amount of voltage applied and controlled by the video signal at each pixel.  The picture is the sum of the illuminated red, green, and blue filtered pixels.

Back Lighting
          LCD TV back lighting is offered in two light types, fluorescent and LED.
 LED lighting uses less energy than fluorescent light bulbs.  And LEDs are much thinner than fluorescent lights. Thin is the significant feature because thin sells.

LED Back lighting
          There are two types of LED back lighting, full-array and edge lit.  Full array is an array of LEDs blocks placed behind the panel.  Edge lit places LEDs along the edge of the TV panel; a rear placed diffuser redistributes light across the entire back of the panel.

Quantum Dot Fix
          LED back lighting does not produce accurate white light.  It leans toward the color blue. That distorts LED back lit LCD red and green light.  Quantum dot film placed between the LED lighting and the LCD layer fixes the problem.
          Quantum dots are nanocrystals that illuminate when 'struck' with LED light.  Q-Dots of different size produce different colored wavelenghts.  A mix of red, green, blue Q-Dots are used to produce more accurate white back light.  The corrected white back lighting produces more accurate color.  Some refer to this as color by blue: the blue is the LED. 

Note Of Caution
          Beware of advertising that obscures the term LCD in the description of an LED backlit LCD TV or Quantum Dot LED backlit filtered TV.  This is an attempt to imply that an LCD TV is an LED TV or a Q-Dot LED LCD TV is a Quantum Dot TV.  Real Q-Dot TV technology exists.  But is not yet marketable.  
OLED is currently the only real LED TV on the market.

Rear Projection LCD TV
          A rear projection LCD TV has the same arrangement as the rear projection CRT: a projector, a first surface mirror, and a set of screens in a large enclosure. However, the CRT projector is substituted with an LCD projector.
          An LCD projector consists of a bright lamp targeted through polarizing mirrors that split and redirect the light with one path each per red-filtered, green-filtered, and blue-filtered LCD mosaic chip.  Each mosaic passes or blocks light per its color video voltage instructions.
          The separate light paths are recombined via another arrangement of polarized mirrors and projected through a set of magnifying lenses to the screen.  Again, the TV screen consists of a Fresnel, lenticular, and protective screen.

DLP
          DLP (digital light projector) features a Digital Micro-Mirror Device or DMD.
The DMD is an integrated chip comprised of a mosaic matrix of microscopic mirrored pixels.
Each micro-mirror, mounted on a pivot, is controlled by an integrated computer chip that electro-statically tilts the individual mirrors a plus or minus ten or twelve degrees.
          An assembly that begins with a bright lamp creates a light beam that is directed through a spinning
color wheel of red, green, and blue filters in route to the mirrors of a single DMD surface.  
 

The tilt of the mirrors reflect and direct the colored light into an empty black area within the projector or through a magnifying lens assembly on route to a projection screen.
        A video digital controller coordinates each mirror’s tilt with the
color wheel to recreate the correct mix and amplitude of red, green, and blue light, which recreates the original picture
       
          Another more costly version of the DLP engages
three separate DMD chips. This version eliminates the color wheel.  As a LCD projector, the light is initially targeted through polarizing mirrors that split the light into three light beams. Each light beam is directed to a red, green, or blue filtered DMD. Each reflected light path is recombined and projected to the screen

DLP Rear Projection
          A DLP rear projection TV has the same arrangement as the rear projection CRT or LCD TV.  A DLP projector is substituted for the CRT or LCD projector.


LYCOS & DILA Projection
          LYCOS & DILA projection TV is an LCD TV of a different polarizing twist.  It’s a bit of a DLP and LCD combined.  Similar to the LCD projector, the LYCOS/ DILA projector includes a bright lamp, a polarizing beam splitting mirror, and three colored filtered LCD mosaics.
The difference is the addition of a mirrored surface behind each LCD mosaic.  
In this case the light is directed through the mosaic and reflected back as it is again redirected through polarized mirrors. The polarizing mirrors recombine and project the light through the magnifying lenses to the screen.
 Now discontinued rear projection versions substituted a LYCOS/DILA projector for the DLP, LCD or CRT projector.
 

OLED & IOLED TV
Organic and Inorganic light emmiting diode television can deliver up to 2160 X 3840 UltraHD resolution.  Both deliver unrivaled contrast and and accurate a gray scale that produces a broader and more accurate color than LCD television.

The Old Diode         
        OLED and IOLED descend from the pioneer of solid-state electronic technology - the diode.  An early example (1906) was crystal radio tuning
via a diode crystal and a 'cats whisker'.  This 'old' diode was fabricated from mineral crystals such as galena (lead crystal).
        A diode allows electric current to pass in one direction, while blocking it in the opposite direction.  This one-way behavior is called rectification.  This trait is demonstrated by the rectifier that converts alternating current to direct current.  
        Diodes are used to regulate voltage, protect circuits from surges, tune radio recievers, generate radio waves, and produce light.  Diodes perform these functions by varying its materials and using a technique of adding impurities called doping.  The materials used include matter such as organic carbon based silicon, or inorganic substances such as germanium.

Electro luminescence
          Light from a diode is derived from the phenomenon of 'electro luminescence'.  This occurs in material that emits light when an electrical current is passed through it.  The color of the light corresponds to the wavelength of the photons.  
Diodes that produce light are the basis of OLED and IOLED TV.  

                                                  The is an illustration of a single LED light.


OLED & IOLED TV
        An OLED and IOLED television screen is a solid-state electronic device.  Each is manufactured as one flat thin plate or even thinner flexible film.  Each is produced via a technolog
y similar to ink-jet printing.  This process will ultimately make each less expensive to manufacture than LCD or plasma TV.  
        The LED screens consists of an electroluminescent layered cell or film situated between anode and cathode electrodes.  The electrodes are a transparent front anode overlay, and a rear metallic (sometimes mirrored) cathode layer. The sandwiched middle electroluminescent cell is comprised of four layers:
   1. A hole-injection positive layer.
   2. A hole-transport layer.
   3. An emissive layer.

   4. An electron-transport negative layer.

        When an appropriate voltage is applied, the injected positive and negative charges recombine in the emissive layer to produce electroluminescent light.  The brightness and color can be enhanced by 'doping' the emissive layer with a small amount of highly fluorescent molecules.  The result is better black level, better contrast, and more accurate color than LCD, plasma, or DLP TV.

How OLED & IOLED differ
        IOLED screens are created on crystal wafers made from inorganic semi-conducting substances such as gallium arsenide or gallium nitride.  OLED wafers are made from organic materials as plastic or glass.  Due to its lower thermal conductivity, an OLED emits less light than IOLED.  (The potential brightness of IOLED is almost 10% of the Sun's brightness.) IOLED also has a longer illuminating life than OLED.  Yet OLED screens still have a lifetime expectancy that is similar to the plasma, LCD, and CRT technologies.
        The key difference is cost.  OLED is less expensive to produce than IOLED.  Plastic and glass cost less than the inorganic crystal wafers.  In addition, it has been reported that OLED manufacturing processing can mass produce a 55 inch OLED screen in about two minutes.   Therefore OLED leads the way in the first waves of real-LED television sales.

Handbook Note: June 2017 - Check out this link regarding a inorganic LED material breakthrough.

The OLED Buzz
        OLED manufacturers will surely attempt to differentiate their OLED from their competitors.  Therefore, get prepared for an advertising avalanche of video 'buzz words'. Here's a short list of 'buzz words' that you may confront.
 
SMOLED / PMOLED
        Some types of OLED displays are described as SMOLED (small molecule) or PMOLED
(passive matrix)
.  They are the same technology.  These displays are controlled one line at a time.  Examples include the displays used in automobile dashboards and the small icons of a MP3 player.

AMOLED (Active Matrix)

        AMOLED uses a thin-film-transistor (TFT) backplane to switch and control each sub-pixel of the display (on/off or more/less bright).  This thin-film matrix switching permits up to UltraHD resolution.  All OLED televisions are based on this active-matrix technology.

Super-AMOLED / WOLED
        WOLED, also reffered to as Super-AMOLED, pairs a fourth white sub-pixel with each set of red, green, and blue sub-pixels to create a complete single pixel.  The extra white sub-pixel produces a brighter picture.  However there are two versions of this technology.
        The first version is manufactured by LG.  Rather than creating a pixel of side by side red, green, and blue OLED sub-pixels; LG 'stacks' a red, a green, and a blue OLED on each other to produce a single sub-pixel.
        The stacked mix of red, green, and blue OLED's creates white light.  The white light of each stack is passed through a red, a green, or a blue filter to create the side by side RGB sub-pixels.  The extra white sub-pixel is simply left unfiltered.
        This LG method may seem odd and unnessarily complex.  But this process is easier and cheaper to manufacture than side by side individual red, green, and blue OLED sub-pixels.
        The second version was manufactured by Samsung.  Their color was produced by electroluminescent side by side red, green, and blue OLEDs.  This may seem more logical but it is more expensive to produce.  Samsung
also included the extra fourth white sub-pixel.
         To date, the lower cost LG method is winning in the market place.  Samsung has pulled their higher cost version from the market.  Sony, Panasonic, and others are implementing the LG panel.

2017  CLEDIS
The Future of Micro LED Displays
          Sony has introduced a 32ft x 9ft  CLEDIS video display.
 CLEDIS is an acronym for 'Crystal LED integrated Structure'; structure as in module.   This screen consists of 144 
18 inch x 16 inch modules
 of 'ultra-fine' red, green, and blue LEDs.   The bezel-less modules are joined together to create large displays that support 10 bit color and HDR content.  
This LED technology is currently aimed at movie theater size commercial displays.  But as improved manufacturing efficiency reduces cost it could become a consumer product.


Video-philes Applaud
        The demise of plasma technology left many 'video-philes' in the lurch.  Yes, plasma is better than LCD.
 But OLED promises even better performance.  Plus OLED and possibly CLEDIS may transform living room walls into television screens of any size.  That could eliminate the video projector and screen from home theater.

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Ed's AV Handbook.com
Batting Practice for the AV Pro and a Primer for the Novice.
Copyright 2007 Txu1-598-288   Revised 2018