Cathode ray tube display system

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(11)

EP 0 318 113 A3

(12)	EUROPEAN PATENT APPLICATION

(88)	Date of publication A3:
	13.09.1989 Bulletin 1989/37

(43)	Date of publication A2:
	31.05.1989 Bulletin 1989/22

(21)	Application number: 88202655.2

(22)	Date of filing: 24.11.1988

(51)	International Patent Classification (IPC)⁴: H01J 29/46, H01J 29/54, H01J 31/12, H01J 29/56

(84)	Designated Contracting States:
	DE FR GB IT

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Priority:

25.11.1987 GB 8727565

(71)	Applicants:
	PHILIPS ELECTRONICS UK LIMITED Croydon CR9 3QR (GB) GB Philips Electronics N.V. 5621 BA Eindhoven (NL) DE FR IT

(72)	Inventors:
	Knapp, Alan George Philips Research Laboratories Redhill Surrey RH1 5HA (GB) Pook, Roger Philips Research Laboratories Redhill Surrey RH1 5HA (GB)

(74)	Representative: Williamson, Paul Lewis et al
	Philips Electronics UK Limited Patents and Trade Marks Department Cross Oak Lane Redhill, Surrey RH1 5HA Redhill, Surrey RH1 5HA (GB)

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References cited: :

(54)	Cathode ray tube display system

(57) A CRT display system in which an electron beam (32) is directed in a plane substantially parallel to a faceplate (14) carrying a phosphor screen (16) the beam (32) being deflected towards the screen.
The position of the beam is controlled to correct for deviation caused, for example, by the influence of ambient magnetic fields. Sensor devices (50, 51) periodically detect during the tube operation deviation of the beam from the desired plane and control deflector electrodes (37) which return the beam to the desired plane. Twisting and lateral shifting of the scanning beam can also be corrected. Beam position sensing is accomplished by overscanning the beam towards the sensor devices during, for example, field blanking periods, so as not to interfere with the display picture.

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