1. Module 5: Digital Techniques and
Electronic Instrument Systems
5.11 Electronic Displays

2. CRT
 Cathode Ray Tube
 Monochrome:
 A heated cathode emits
electron beams,
accelerated by magnetic
fields and collide in a
phosphor coating screen.
The collision emits light.
 Color:
 Three cathodes emit one
electron beam for each
color (RGB). Each pixel of
the screen contains 1
phosphor dot for each
color. Each beam collides
only with the
corresponding phosphor
dot of each pixel.
 The CRT contains:
 A heated cathode
 Accelerating magnetic field
 A phosphor coating

3. Monochrome CRT
 The input of
each plate is a
combination of
the input signal
and a sawtooth
wave.
 The refresh rate
is around 70Hz.

4. Color CRT
 By controlling the
intensity of each beam,
various colors can be
obtained.

5. LCD
 Liquid Crystal Displays.
 The polarization of light:
 Liquid crystals are organic
compounds that exhibit both
solid and liquid properties.
 A property of liquid crystals is
that they can be reoriented by
an electric field.
 2 polarization filters are placed
with 90 degrees angle with
each other.
 The polarized light that exits
the first polarization filter is
reoriented by the liquid
crystals by 90 degrees and
passes through the second
polarization filter.
 If an electric filed is applied to
the liquid crystals, the light is
not reoriented and does not
pass the second filter.

6. Color LCD
 Each pixel is divided
to three sub-pixels:
RGB.
 A color filter is placed
in front of each sub-
pixel.

7. TFT LCD Screens
 Thin-film-transistor
LED technology (1
transistor switching
each sub-pixel)
enables higher
resolutions and fast
response time.

8. (O)LED displays
 (Organic) LED displays
use the LCD
technology, but the
backlight provided by
a LED panel.
 Each LED emits light
when supplied with 1.7
to 3V.

9. CRTs vs. LCDs.
 CRTs:
 Low resolutions
 Generate magnetic fields
 Heavy, require depth behind the front
panel
 Heating problems
 Excellent viewing angle
 Response time: 1msec.
 LCDs:
 Higher resolutions and image quality
 Power efficient
 Thinner, lighter than CRTs
 Poor viewing angle, but better in newer
models and excellent in OLEDs.
 Response time: 1-8msec for LED and
sub-ms for OLED. Sluggish in low
temperatures.