5.11 Electronic displays Flashcards
Incandescent displays require thin filaments for each segment, similar to regular lamps. Another type of display used was the gas-discharge tube. This older type of unit operated at high voltages and emitted an orange glow.
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electronic displays in modern aircraft are using the following technologies:
Cathode Ray Tube (CRT)
Light Emitting Diode (LED)
Organic LED (OLED)
Liquid Crystal Display (LCD)
the cathode ray tube uses the same principle as an
oscilloscope
A cathode ray tube is a thermionic device consisting of an evacuated envelope. Inside, an electron gun is positioned as well as the beam focussing system.
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CRTs operate using an electron gun. These generate images by emitting electrons and using a series of anodes to manipulate the image
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The data received by a human eye can be considered by it
wavelength and brightness
what are the three primary colours
red
green
blue
The mixing of coloured light is known as ‘additive’ mixing This differs from the mixing of dyes or pigments which is
‘subtractive’ and uses yellow, cyan and magenta as primary colours.
CRT advantages
coloured multifunctional displays
CRT disadvantages
long shape, that takes up a lot of space
Heavy
Warming up required (approximately 10 seconds)
High power consumption
Thermal sensitivity
Tend to burn-in (require screen savers)
LED advantages
small dimensions
robust
long lifetime
LED disadvantages
high current consumption (compared with LCD)
limited flexibility
the two common types of LED display formats are
the segment display
the dot matrix display
While LEDs give off light, Liquid Crystal Displays (LCDs) are not light sources themselves, but control light
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Modern LCDs have a sandwich-type structure of layers
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LCDs do not emit their own light in the way CRTs do. There are three viewing modes:
Reflective
Transmissive
Transflective
Reflective displays require ambient light to be seen.
Digital watches, calculators and many other electronic appliances use reflective displays.
Transmissive displays have a clear polariser on the front and the back. The display therefore depends on light coming through from the back of the display toward the observer in order to be seen
Most, but not all, transmissive displays are negative image
The transmissive mode uses no reflected light relying entirely on edge-lighting or back-lighting
Transflective displays have a rear polariser that includes a translucent material which reflects part of the ambient light and transmits backlighting. As the name implies, it is a compromise between the transmissive and reflective viewing mode
The downside of these are the higher costs and the reduced contrast ratios.
The polariser acts as a one way filter for the light, allowing the light from the backlight to pass through the layers of the LCD Panel to the viewer but not the light from the outside environment to pass the opposite way
The type of polariser usually found in LCD screens is the transflective type
three sub-pixels of red green and blue make up one screen pixel on the display.
The colour filter layer gives each pixel on the screen its own colour
the most common used in LCD screens is known is the
Thin Film Transistors (TFT)
The backlight is responsible for putting light through the sandwiched layers all the way to your eyes where you see the image illuminated
These can be Cold Cathode Fluorescent Lamps (CCFLs) or LED backlighting
usually placed on bottom of screens but on better quality screen they are on top and bottom
LCD advantages
Flat
High-quality picture
Well illuminated
Multifunctional displays
Low energy consumption
Long lifespan
Virtually no maintenance is required
LCD disadvantages
Temperature-sensitive – the fluid can freeze.
If used for Electronic Flight Instrument System (EFIS), Electronic Centralised Aircraft Monitor (ECAM), or Engine-Indicating and Crew-Alerting System (EICAS) displays, they must be operated in a certain temperature range to ensure high-quality pictures and fast reaction.
After a while the LCD display the some of the pixels stop working or display a discoloured spot on a black spot.
The viewing angle of an LCD display is very limited due to the automatic pixel tracking/phase controls.
a liquid crystal display made of a matrix of cells
known as passive-matrix LCD technology
OLED stands for Organic Light-Emitting Diode, the ‘organic’ referring to the
carbon film that sits inside the panel before the glass screen.
OLED panels emit their own light when an electric current is passed through, whereas cells in an LCD or LED display require an external light source, e.g. the backlight for brightness
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OLED technology has several advantages over LCD technology:
The colours are brighter.
The screen can be read from a side view, as well as vertically.
Screens are thinner and can even be flexible.
Its power consumption is also much lower, as no back-light is required.
PMOLEDs are most efficient for text and icons and are best suited for small screens (2- to 3-inch diagonal). Even with the external circuitry, passive-matrix OLEDs consume less battery power than LCDs.
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(PMOLED) stands for
Passive-matrix OLED
AMOLEDs consume less power than PMOLEDs because the TFT array requires less power than external circuitry, so they are efficient for large displays
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The best uses for AMOLEDs are
computer monitors, large-screen TVs and electronic signs
AMOLED stands for
Active-matrix OLED
The display chipset comprises three line-replaceable units:
parts of the HUD
The HUD computer, which receives and processes the data and generates the graphics.
The projector unit.
The fold-down optical combiner, which aligns the graphic overlay and the real-world view.
CRTs operate using an electron gun. These generate images by emitting electrons and using a series of anodes to manipulate the image
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oscilloscopes use an alternative method of deflecting the beam called
electrostatic deflection
In this method, two metal plates are placed opposite each other, like a capacitor between the plates. By varying the potential across the plates, the strength of the electric field can vary
Reflective displays have an opaque rear polariser that includes a diffuse reflector, such as brushed aluminium
This layer reflects polarized ambient light, that has entered the front of the display, back through the LCD cell. Reflective displays require ambient light to be seen
Head-up displays used to be based on cathode ray tube technology; they currently use what
liquid crystal displays
