Electric lamp and discharge devices: systems – Plural power supplies – Plural cathode and/or anode load device
Reexamination Certificate
1997-02-12
2001-05-22
Vu, David (Department: 2821)
Electric lamp and discharge devices: systems
Plural power supplies
Plural cathode and/or anode load device
C315S168000, C250S208200
Reexamination Certificate
active
06236164
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to vacuum electron devices and particularly relates to electron current sensing in vacuum electron devices.
2. Background Description
A conventional vacuum electron device comprises an cathode and 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 in a beam. A beam current thus flows between the anode and the cathode. In some conventional vacuum electron devices, such as cathode ray display tubes (CRTs), one or more grid electrodes are disposed between the cathode and the anode. In operation, a control voltage is applied to each of the one or more grid electrode(s). The control voltage imposes an electrostatic force on the electron beam. The electron beam current can be adjusted by adjusting the control voltage. The control voltage is typically generated by a control sub-system of the circuit containing the vacuum electron device. In a CRT display, this control sub-system controls the brightness of the picture produced on the screen. In general, such control systems are open loop systems. In such a system, there is no feedback provided between the beam current flowing and the control voltage applied to the grid electrode. In conventional CRT displays, indirect feedback of the beam current is provided by measuring by sensing the current flowing in the anode voltage generator. This technique provides useful control information for controlling a vacuum electron device in which there is only a single electron beam, such as monochrome CRTS. This technique is also suitable for controlling total beam current in a multiple beam vacuum electron device such as a colour cathode ray tube. However, this technique is not suitable for controlling individual beam current in such a device because the individual beam currents are effectively summed at the anode.
SUMMARY OF THE INVENTION
In accordance with the present invention, there is now provided a vacuum electron device comprising an evacuated envelope containing a cathode for supplying electrons to form an electron beam, an anode spaced from the cathode for receiving the electron beam, and a sensor electrode located between the cathode and the anode.
Preferably, the sensor electrode extends into the path of the electron beam from the cathode to the anode.
The sensor electrode may comprise a triangular portion having a tip located on the center axis of the path of the electron beam. Alternatively, the sensor electrode may comprise an elongate portion extending between diametrically opposite sides of the path of the electron beam.
In preferred embodiments of the present invention, the device further comprises a grid electrode disposed between the cathode and the sensor electrode, a grid voltage generator for generating a control voltage on the grid electrode to control electron beam current flowing from the cathode to the anode, and feedback means connected to the grid voltage generator for varying the control voltage in response to a sense current detected from the sensor electrode to maintain a reference electron beam current.
The feedback means preferably comprises a variable bias means for determining the reference beam current.
In particularly preferred embodiments of the present invention, the cathode comprises an area cathode.
The feedback means preferably comprises drive means for varying a drive voltage supplied to the area cathode in response to the sense current detected by the sensor electrode.
The present invention extends to a cathode ray tube display comprising a vacuum electron device as hereinbefore described. The present invention also extends to a field emission display comprising a vacuum electron device as hereinbefore described. Furthermore, the present invention extends to a magnetic matrix display comprising a vacuum electron device as hereinbefore described.
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Beeteson John
Knox Andrew Ramsay
International Business Machines - Corporation
Scully Scott Murphy & Presser
Underweiser, Esq. Marian
Vu David
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