Method and apparatus for reducing electromagnetic interference radiated by cathode ray tube displays
US6020939A · kind A · utility
Assignee
Inventors
Key dates
| Filing date | Jan 19, 1996 |
| Grant date | Feb 1, 2000 |
| Priority date | — |
| Expiry date | Jan 19, 2016 |
Classification
- Technology area (CPC H)Electricity
- CPC primaryH01J2229/0015
- WIPO fieldAudio-visual technology
- WIPO sectorElectrical engineering
Abstract
Electromagnetic interference ("EMI") is reduced in a CRT video display system by spreading-out the EMI-producing spectra present in the video pixel data and/or clock signals. A clock dropping circuit coupled between the display generator main oscillator and the timing generator periodically phase-modulates the timing generator clock signal such that it comprises N phases, where N.gtoreq.2. As a result, each horizontal line of video data and the horizontal synchronization signals is phase shifted. This dual-shifting effect eliminates display image distortion that would result if only the video signal were shifted. Video distortion is further minimized by deriving the horizontal and vertical synchronizing signals from a common constant clock. EMI energy associated with each clock harmonic is spread by a frequency amount .DELTA.f proportional to the rate of phase change in the clock signal, the rate of phase change exceeding half the bandwidth f.sub.m of a standard EMI measurement reference window. This disperses adjacent spectral energy sufficiently so the reference window measures but one, decreased, amplitude at a time.
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.