Electric lamp and discharge devices: systems – Plural power supplies – Plural cathode and/or anode load device
Reexamination Certificate
1998-02-19
2001-02-27
Vu, David (Department: 2821)
Electric lamp and discharge devices: systems
Plural power supplies
Plural cathode and/or anode load device
C315S366000, C313S495000
Reexamination Certificate
active
06194838
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to matrix addressed electron beam displays and particularly to a self stabilizing non-thermionic cathode for use in matrix addressed electron beam displays.
BACKGROUND OF THE INVENTION
Flat panel electron beam displays comprise a cathode and an anode contained in an evacuated envelope. In operation, the cathode is held at a negative potential relative to the anode. Electrons are emitted from the cathode. The potential difference between the cathode and the anode accelerates the emitted electrons from the cathode towards the anode. This is formed, within the display, into a beam. A beam current thus flows between the anode and the cathode. In flat panel electron beam displays a matrix arrangement is disposed between the cathode and the anode. The matrix arrangement is formed by a pair of “combs” placed at right angles to each other. These are commonly referred to as rows and columns. Each pixel or subpixel lies at the intersection of a row and a column. Each of the combs has many separate elements (rows or columns). In operation, a control voltage is applied to each element of each of the combs. The control voltage applied to each element imposes an electrostatic force on the electron beam associated with that element. The electron beam current associated with that element can be adjusted by adjusting the control voltage.
Matrix driven flat CRT displays require the use of an area cathode to provide a uniform source of electrons to each pixel aperture. Thermionic cathodes can be used, but these require heating to obtain emission, with its consequent problems of power dissipation and thermal management for the other parts of the flat CRT display. Field emission electron sources such as MIMs, PFEs and FEDs do not require heating, but are non space charge limited and suffer from problems of uniformity and instability that require some form of smoothing to make their use practical.
SUMMARY OF THE INVENTION
In accordance with the present invention, there is now provided an electron source comprising non-thermionic cathode means and control grid means wherein the control grid means controls a flow of electrons from the cathode means and the electrons are formed into one or more electron beams for guidance towards a target, the control grid means having an insulating layer located on a side facing the cathode means, the surface of the insulating layer facing the cathode being at a predetermined distance from the control grid and being perforated with one or more apertures for each of the one or more electron beams.
The technique can be used to make a non-thermionic cathode into a self limiting space charge electron source, with the advantages of the inbuilt smoothing and averaging that space charge operation implies.
An isolated, conducting layer is preferably formed on the surface of the flat insulated layer facing the cathode. In a preferred embodiment, the conducting layer may be connected to a controlled leakage resistance. A voltage measuring device may be connected to the conducting layer. The conducting layer helps to prevent local charge changes and ensure that the insulating layer has a uniform potential. The controlled leakage resistance allows the insulating layer voltage to respond to reductions as well as increases in electron accumulation.
Preferably, the cathode means comprises a Metal Insulator Metal or a printed film emitter device.
In a further embodiment, the cathode is divided into stripes, each stripe corresponding to a drive line of a display, and the stripes are turned on, only when required. This means that the cathode can be pulsed on only when required and can run at a low duty cycle of perhaps 0.1%. This will allow the emitter life to be extended.
Preferably, the insulating layer extends down to the cathode in spaces between the drive lines of a display.
Further preferably, the electron source further comprising an isolated, conducting layer formed on the internal surfaces of the channels formed by the insulating layer. The conducting layer helps to prevent local charge changes and ensure that the insulating layer has a uniform potential. A controlled leakage resistance may be connected to this layer to allow the insulating layer voltage to respond to reductions as well as increases in electron accumulation. The isolated, conducting layer may be formed on the internal surface, facing the cathode, of the channels formed by the insulating layer.
Preferably, the stripes in the cathode are turned on one line before they are required. This provides time for the electron cloud to build up before beam current is extracted.
The invention also provides a display device comprising: an electron source as described above; a screen for receiving electrons from the electron source, the screen having a phosphor coating facing the side of the collimation block remote from the cathode; and means for supplying control signals to the control grid means and anode means to selectively control flow of electrons from the cathode to the phosphor coating via the channels thereby to produce an image on the screen.
Also provided by the invention is 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 described above for displaying data processed by the processor means.
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patent: 3935500 (1976-01-01), Oess et al.
patent: 5070282 (1991-12-01), Epsztein
patent: 5272419 (1993-12-01), Park
patent: 5760548 (1998-06-01), Beeteson et al.
patent: 5939842 (1999-08-01), Beeteson et al.
patent: 0 213 839 (1986-08-01), None
patent: 0 685 869 (1995-05-01), None
Beeteson John Stuart
Knox Andrew Ramsay
Pietrzak Christopher Carlo
Herzberg Louis P.
International Business Machines - Corporation
Vu David
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