Magnetic Scan Magnification for CRT

Publishing Venue

IBM

Related People

Langner, GO: AUTHOR

Abstract

A magnetic lens can be utilized to provide a wide-angle deflection at the screen of the cathode ray tube under the control of a relatively narrow angle deflection system at the neck of the tube. This enables the use of electrostatic deflection control at reasonable voltages or the use of a compact magnetic yoke design with attendant advantages.

Magnetic Scan Magnification for CRT

A magnetic lens can be utilized to provide a wide-angle deflection at the screen of the cathode ray tube under the control of a relatively narrow angle deflection system at the neck of the tube. This enables the use of electrostatic deflection control at reasonable voltages or the use of a compact magnetic yoke design with attendant advantages.

The cathode ray tube has electron gun structure 1 and focus lens 2 which can be magnetic or electrostatic. The electron beam is deflected by magnetic yoke 3, which can operate at small deflection angles such as less than +/- 10 degrees. Thus, the center of deflection can be assumed to be the center of yoke
3. Alternatively, an electrostatic deflection arrangement can operate at relatively low voltages such as 300 to 1,000 volts.

Since the deflection is small, the aspect ratio, length to diameter, of yoke 3 can be relatively large, or in the case of electrostatic deflection, the deflection plates can be relatively long.

Axially symmetric electron lens 4 forms an enlarged real image of plane 5 on screen 7. Lens 2 focuses the beam at plane 5 and this focused image is seen on an enlarged scale at screen 7. Thus, the original deflection angle 8 is effective to achieve a maximum deflection angle 9 in the operation of the tube.

Lens 4 is of the axially symmetrical, double-gap type with opposite magnetization of the two gaps to avoid anisotropic distortion. It surrounds a portion 6 of the neck w...