Page 788 - Automotive Engineering Powertrain Chassis System and Vehicle Body

Automotive instrumentation and telematics C HAPTER 23.1

conditions. The primary disadvantage of such ad hoc messages appear. At the rear is a somewhat complex
display devices is the limited flexibility of the displayed structure called an electron gun. This device generates
messages. a stream of electrons that is accelerated toward the
Arguably the display device with the greatest flexi- screen and brought to convergence at a spot on the
bility for presenting all types of data (including pictorial screen. A system of coils in the form of electromagnets
representations) is the CRT. The CRT is familiar to us all causes this convergence of electrons (or beam) and is
as the TV picture tube, although it has also been used for referred to as the magnetic focusing system. The focused
personal computer monitors. Recently a solid-state stream of electrons is called the beam.
equivalent to the CRT has been developed that yields The electron beam generates a spot of light at the point
a flat panel display having all of the display capabilities of on the screen. The intensity of the light is proportional to
the CRT. the electron beam current. This current is controlled by
The CRT (or its solid-state equivalent) is being used the voltage (V c ), which is called the video signal, on an
increasingly for display purposes in the aerospace in- electrode that is located near the electron gun. A color
dustry, where it is used to display aircraft attitude in- CRT has three separate electron gun structures, with each
formation (sometimes pictorially), aircraft engine or focused on one of three dots at each picture location on
airframe parameters, navigational data, and warning the screen corresponding to red green blue (RGB).
messages. Clearly, the CRT-type display has great po- A solid-state LCD display consists of an array of LCDs
tential for automotive instrumentation display. arranged in a matrix format as depicted in Fig. 23.1-20b.
A technology that has the same flexibility of display as In this structure, only one LCD is active at any time. The
the CRT is the solid-state equivalent of a CRT. Such color and intensity of the active LCD is controlled by
a display is sometimes called a flat-panel display. How- circuitry connected within the microstructure. The
ever, as it is functionally equivalent to the CRT and as active LCD is selected via horizontal and vertical de-
the CRT is an existing, very mature technology, we first tection circuitry. In the solid-state CRT equivalent, each
explain the CRT operation example. This solid-state pixel has its own address.
equivalent of the CRT can be implemented in a number In the majority of applications (including TV), the
of technologies such as an LCD array. CRT electron beam is scanned in a pattern known as
Fig. 23.1-20 is a sketch of a typical black and white a raster by means of specially located electromagnets (see
CRT. It is an evacuated glass tube that has a nominally flat Fig. 23.1-20). The magnetic fields created by the scan-
surface that is coated with a phosphorescent material. ning coils deflect the beam horizontally and vertically.
This surface is the surface or face on which the displayed The amount of deflection is proportional to the current

HORIZONTAL
DEFLECTION
CIRCUITRY

ACTIVE
PIXEL
VERTICAL
DEFLECTION
CIRCUITRY

INTENSITY COLOR

Fig. 23.1-20(b) Solid-state CRT.

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