Picture reproduction apparatus with a cathode ray tube and an arrangement for measuring the beam current
US4987350A · kind A · utility
Assignee
Inventors
Key dates
| Filing date | Sep 1, 1989 |
| Grant date | Jan 22, 1991 |
| Priority date | — |
| Expiry date | Sep 1, 2009 |
Classification
- Technology area (CPC H)Electricity
- CPC primaryH04N9/645
- WIPO fieldAudio-visual technology
- WIPO sectorElectrical engineering
Abstract
A video-display unit in which the beam current of a cathode-ray tube is measured for a predetermined time interval during display of some lines exterior to an image, for establishing automatic cutoff for the electronic beam. This electron beam is defocused during that predetermined time interval, and the defocusing is independent of the contents of the image, so that initial lines are substantially invisible. An electronic switch may be provided for decreasing the focusing voltage of the cathode ray tube. The electronic switch may be a high-vacuum tube connected to the focusing electrode of the cathode-ray tube, or this switch may be a transistor connected through a transformer to the focusing electrode. The transformer may be attenuated.
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.