International Business Machines Corporation

Brian D Chase

Peter Burr

Andrew Paton

Brian R Sowter

A color CRT has stripes of different color light emission phosphors (r, g and b) deposited on a faceplate of the tube with the relative widths of the stripes being inversely proportional to the light emission efficiency of the phosphors. By this means the integrated brightness of the emitted light from the different phosphor stripes is the same for the same value beam current. By using a novel double shadow mask arrangement, the widths of the beams from the three guns can be made to match, or substantially to match, the widths of the phosphor elements on which they land. Specifically, the beam from one gun is aligned with apertures through both masks in order to transmit a relatively wide portion of the beam onto the least efficient, phosphor. The portion of the beams transmitted by the first mask for the other two guns are further clipped by the relatively off-set apertures in the second mask. This arrangement enables the advantage of the balanced color output from the screen to be enjoyed without loss of purity margin and provides a significant increase in brightness for a given beam current and/or resolution of the screen. The invention is applicable to CRTs employing shadow masks with slots and phosphor stripes, or holes and phosphor dots and also for CRTs driven in raster scan or vector mode.

Shadow mask color CRT with enhanced resolution and/or brightness

A convergence unit for an in-line color cathode ray tube consists of two E-shaped cores, preferably formed of strip-shaped soft-magnetic material. Each E-core has two relatively long limbs extending from a central relatively short pole piece to end relatively short pole pieces windings extend around the limbs which are substantially parallel to a tangent to the neck of the CRT so that the magnetic fields due to individual turns reinforce the magnetic fields between the pole pieces. Preferably each E-core has each of its two windings extending over both limbs, one being reverse wound, so that the mutual inductance between the two windings is zero.

Convergence unit for in-line color cathode ray tube

A convergence unit for an in-line color cathode ray tube consists of four E-cores located around the neck of the CRT. Each E-core, preferably consisting of strip-shaped soft-magnetic material such as mumetal or permalloy, carries two coils connected so that the net magnetic field at the central beam is zero. The E-cores are arranged in paris with the resultant fields at the nearer electron beam due to each individual E-core being substantially orthogonal to one another.

The dimensions and light output of a beam in a shadow mask cathode-ray tube are determined by means of an optical system 7 focussed on a phosphor dot to pick up and record the light generated by a ray 4 passing through a single aperture 6 in the shadow mask 2. The cathode-ray beam 1 is moved so that the whole cross-section of the beam passes the aperture 4. The detected light outputs are plotted to provide an accurate representation of the whole beam. Repeating the procedure for each gun gives a precise record of the misconvergence of the beam

Method and apparatus for determining beam dimensions at the screen of a

Convergence of the beams of an in-line gun shadow mask cathode-ray tube is provided by windings on a common core and generating pairs of quadruple and six-pole magnetic fields, respectively. The core is provided with non-magnetic ribs each having a projection for the purpose of locating the windings.

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Eastleigh, United Kingdom

Brian D Chase