Display device

A display device comprises a cathode means for emitting electrons and a permanent magnet having a two dimensional array of channels extending between opposite poles of the magnet. The magnet generates, in each channel, a magnetic field for forming electrons from the cathode means into an electron beam. A screen receives an electron beam from each channel, the screen having a phosphor coating facing the side of the magnet remote from the cathode, the phosphor coating comprising a plurality of areas, each area being capable of illumination, at least one of the areas being capable of illumination by a plurality of the electron beams. Grid electrode means are disposed between the cathode means and the magnet for controlling flow of electrons from the cathode means into each channel, the grid electrode means comprising a plurality of elements each element corresponding to a different area of the phosphor capable of illumination. First anode means is disposed between the magnet and the screen for accelerating the electron beam towards the screen.

FIELD OF THE INVENTION 
The present invention relates to a magnetic matrix display device and more 
particularly to a fixed format display for use in laboratory equipment, 
car dashboards, flight cockpits and the like. 
BACKGROUND OF THE INVENTION 
Fixed format displays are displays where the changes in displayed 
information are achieved by the selective illumination of portions of the 
display, possibly in different colors. A fixed format display, unlike a 
general purpose display is usually only useable for a particular 
application. A limited control function, typically only the display 
brightness is provided. 
SUMMARY OF THE INVENTION 
In accordance with the present invention, there is now provided a display 
device comprising cathode means for emitting electrons, a permanent 
magnet, a two dimensional array of channels extending between opposite 
poles of the magnet, the magnet generating, in each channel, a magnetic 
field for forming electrons from the cathode means into an electron beam, 
a screen for receiving an electron beam from each channel, the screen 
having a phosphor coating facing the side of the magnet remote from the 
cathode, the phosphor coating comprising a plurality of areas, each area 
being capable of illumination, at least one of the areas being capable of 
illumination by a plurality of the electron beams, grid electrode means 
disposed between the cathode means and the magnet for controlling flow of 
electrons from the cathode means into each channel, the grid electrode 
means comprising a plurality of elements each element corresponding to a 
different area of the phosphor capable of illumination, and first anode 
means disposed between the magnet and the screen for accelerating the 
electron beam towards the screen. 
At least one area of the phosphor being capable of illumination by a 
plurality of the electron beams means that area of phosphor can be thought 
of as having multiple electron beams associated with it, all of the 
associated electron beams being present together or none of the electron 
beams being present. The individual beams are not separately addressable. 
Areas of phosphor having a plurality of electron beams associated with 
them can be mixed with areas having a single electron beam associated with 
them. 
In preferred embodiments of the invention, each of the areas of phosphor 
capable of illumination corresponds to a plurality of electron beams. The 
plurality of electron beams, although generated in separate channels in 
the magnet, are controlled by a single grid electrode means and are either 
all allowed into or all blocked from the channels. 
The cathode means may be present over substantially all of the substrate on 
which it is located or it may be present only in those areas corresponding 
to the areas of phosphor. 
Each of the phosphor areas may produce visible light of the same color, 
that is the display of the present invention corresponds to a monochrome 
display, which may be, for example, green, white, amber or any color in 
which phosphors are available. In the alternative, some of the phosphor 
areas may emit visible light of a different color to others of the 
phosphor areas, that is the display of the present invention is more 
similar to a color display. The display of the present invention differs 
in front of screen appearance and function from a conventional display in 
that each of the phosphor areas on the screen is only ever capable of 
displaying a single color. However, phosphor areas of any of the colors of 
phosphor which are available can be used. 
The display of the present invention is particularly suited for use in 
vehicles, such as in a car dash board or in an aircraft flight cockpit. 
The present invention also provides a computer system comprising memory 
means, data transfer means for transferring data to and from the memory 
means, processor means for processing data stored in the memory means, and 
a display device as for displaying data processed by the processor means.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
An embodiment of the invention will now be described by means of an example 
application of the invention to a temperature gauge. The display is 
required only to display information in a fixed format, in this case to 
illuminate one of a number of colored segments of the display. The color 
of the segment and its relative position indicate the temperature. Blue 
segments are used to represent cold, green segments are used to represent 
normal, yellow segments are used to represent caution and red segments are 
used to represent warning. Within the areas of segments of each color, the 
position of the segment which is illuminated also conveys information. For 
example, if a green segment which is immediately adjacent to the yellow 
segments is illuminated, then although the temperature is normal, any 
increase will result in a yellow caution segment being displayed. The 
intensity of the illumination of the segment is controlled to compensate 
for, for example, the ambient illumination level and user preferences. The 
segment may be singly lit with all others extinguished, or may be brightly 
lit, with all others dimly lit, that is there is enhanced contrast for the 
active segment. 
Referring first to FIG. 1, a magnetic matrix display of the present 
invention comprises a first glass plate 10 carrying a uniform area cathode 
20, covering the entire display area and a second glass plate 90 carrying 
a coating of phosphor stripes 80 facing the cathode 20. In another 
embodiment, the area cathode 20 is only present on the glass plate 10 in 
regions where electron beam current is required. The phosphors are 
preferably high voltage phosphors. The phosphor stripes may all be the 
same color or they may of different colors arranged according to the 
desired output required on the display. Unlike a conventional display 
which has three primary colored phosphors which are mixed in various 
proportions to produce the range of colors available, the color of the 
light output is dictated by the color of light the particular phosphor 
produces. 
In the example of FIG. 1, the phosphors are arranged as a row of two blue 
phosphor stripes, twelve green phosphor stripes, two yellow phosphor 
stripes and three red phosphors. A final anode layer (not shown) is 
disposed on the phosphor coating 80 and is connected to an EHT supply to 
provide the electron beam with sufficient energy to cause efficient usage 
of the electron beam current in producing visible light from the 
phosphors. A permanent magnet 60 is disposed between glass plates 90 and 
10. The magnet is perforated by a two dimension matrix of perforations or 
"pixel wells" 70. An anode 50 is formed on the surface of the magnet 60 
facing the phosphors 80. For the purposes of explanation of the operation 
of the display, this surface will be referred to as the top of the magnet. 
This anode covers the entire top side of the magnet and the voltage which 
is applied to this anode enables the anode to provide the field gradient 
to accelerate the electrons through the pixel wells and allows the anode 
to operate in conjunction with the grid electrodes to attract electrons 
into the pixel wells. 
A plurality of control grid stripes 40 are formed on the surface of the 
magnet 60 facing the cathode 20. For the purposes of explanation of the 
operation of the display, this surface will be referred to as the bottom 
of the magnet. The control grid stripes 40 comprise a group of parallel 
control grid conductors extending across the magnet surface in a column 
direction so that each phosphor stripe 80 is associated with a control 
grid stripe and with one or more of the perforations or "pixel wells" 70 
in the magnet. The control grid stripes 40 could be arranged in a row 
direction, or arranged as areas, but will always correspond to areas of 
the phosphor with which they are associated. 
Plates 10 and 90, and magnet 60 are brought together, sealed and then the 
whole is evacuated. In operation, electrons are released from the cathode 
and attracted towards control grid stripe 40. Control grid stripe 40 
provides an addressing mechanism for selectively admitting electrons to 
pixel wells 70 in the magnet corresponding to each of the phosphor 
stripes. The voltage applied to each of the control grid stripes is 
switched between a non-select level where electrons are blocked from 
entering the pixel wells and an "on" level where the electrons are allowed 
to enter the pixel wells. Electrons pass through grid 40 into a pixel well 
70. In each pixel well 70, there is an intense magnetic field. The anode 
50 at the top of pixel well 70 accelerates the electrons through pixel 
well 70. Electron beam 30 is then accelerated towards a higher voltage 
anode formed on glass plate 90 to produce a high velocity electron beam 30 
having sufficient energy to penetrate the anode and reach the underlying 
phosphors 80 resulting in light output. The higher voltage anode may 
typically be held at 10 kV. 
FIGS. 2 to 4 show components of the display as viewed from the front of the 
display seen by the user. FIG. 2 shows the glass plate 90 having phosphor 
stripes 80. In the embodiment shown, there are two blue stripes, twelve 
green stripes, two yellow stripes and three red stripes. The green stripe 
sixth from the left is shown highlighted, since this is the "active" zone 
or the one presently illuminated. 
FIG. 3 shows the magnet used. The magnet is perforated with pixel wells, 
each pixel well corresponding to an electron beam and groups of adjacent 
pixel wells and their respective electron beams being associated with each 
of the phosphor stripes. The patterning of pixel wells in the magnet 
corresponds to the patterning of the first anode 50 on the surface of the 
magnet facing the phosphor coated glass plate. 
FIG. 4 shows the grid conductors 40 laid out in strips with numerous 
apertures for each segment corresponding to pixel wells in the magnet. A 
connection is provided to each of the grid conductors 40 for a control 
voltage to be applied to each of the grid conductors. The control voltage 
is modulated to control the beam current entering that pixel well 70. 
Controlling the beam current controls the number of electrons subsequently 
striking the colored phosphor stripe 80 with which the grid electrode 40 
is associated and hence the intensity with which the phosphor stripe 80 is 
illuminated. 
FIG. 5 shows a section through the display of FIG. 1 including the phosphor 
coated glass screen of FIG. 2, the magnet of FIG. 3 and the grid 
conductors of FIG. 4. In FIG. 5, one of the areas of phosphor is shown 
brightly lit, with the other areas of phosphors shown dimly lit. Starting 
from the rear of the display, the cathode 20 is shown having electrons 
leaving it, the flow of those electrons being controlled by grid 
electrodes 40, which either allow or block the entry of electrons into the 
pixel wells 70 formed in the magnet 60. The electron beams which are 
allowed into the pixel wells 70 in the magnet 60 are attracted to a first 
anode 50 located on the front surface of the magnet. After exiting the 
pixel wells the electrons are attracted to a final anode 75 which consists 
of an aluminum backing to the colored phosphor stripes 80. This aluminum 
backing 75 is connected to an EHT supply and provides the electrons with 
sufficient energy to produce visible light output from the colored 
phosphors. At the front of the display is the glass plate 90 carrying the 
phosphor stripes 80. 
Unlike a general purpose display, a matrix addressing technique is not used 
for a display according to the present invention. Thus the duty cycle of 
electrons hitting the phosphor stripes is 100%. This contrasts with a 
general purpose matrix addressed display having 1280 pixels horizontally 
and 1024 pixels vertically which has a duty cycle of less than 0.1%. The 
beam current required for a given light output is reduced by the ratio of 
the duty cycle. For a general purpose matrix addressed display, a light 
output of 100 Cd/m2 requires in the region of 200 nA per pixel with a duty 
cycle of 0.1%. In a display according to the present invention, the beam 
current required for the same light output is only 200 pA, that is one 
thousandth part of that required for a matrix addressed display. 
When a display is used in an office environment, the ambient light range is 
typically 500 to 1000 lux. This corresponds to 156 to 318 Cd/m2 from a 
perfect diffusing source. A display light output of 100 Cd/m2 is 
sufficient to maintain a high enough contrast ratio between "active" and 
"inactive" display segments. 
However, when a display is used in, for example, a car dashboard, the 
ambient light range experienced is far greater than in an office 
environment. On a bright sunlit day the ambient light may be 10,000 lux, 
whilst at night it may be only 10 lux. This range corresponds to 3183 to 3 
Cd/m2 from a perfect diffusing source, a very wide range of ambient 
illumination over which the display must operate. A high contrast ratio 
between "active" and "inactive" display segments is needed. Hence a range 
of required light outputs from the display of 1 to 1000 Cd/m2 is needed, 
corresponding to beam currents of 2 pA to 2 nA for a display according to 
the present invention. 
Although the present invention and its advantages have been described in 
detail, it should be understood that various changes, substitutions and 
alterations can be made herein without departing from the spirit and scope 
of the invention as defined by the appended claims.