Method and apparatus for reducing electromagnetic interference radiated by flat panel display systems
US5659339A · kind A · utility
Assignee
Inventors
Key dates
| Filing date | Sep 30, 1994 |
| Grant date | Aug 19, 1997 |
| Priority date | — |
| Expiry date | Sep 30, 2014 |
Classification
- Technology area (CPC H)Electricity
- CPC primaryH04B2215/064
- WIPO fieldAudio-visual technology
- WIPO sectorElectrical engineering
Abstract
Electromagnetic interference ("EMI") generated by a flat panel video display system is reduced by periodically phase/modulating the panel clock. This spreads EMI energy associated with each panel clock harmonic by a frequency amount .DELTA.f proportional to the rate of phase change in the panel clock signal. EMI energy associated with each panel clock harmonic is reduced relative to a square-wave panel clock signal because the same energy is now spread over a group of frequencies centered about each harmonic. The phase of the panel clock is changed at a rate exceeding 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. Phase-modulation may be achieved using a clock pulse dropping circuit that receives a square-wave input of frequency Nf.sub.c from a main oscillator, drops at least one clock pulse out of a stream of M clock pulses, and frequency divides the resultant waveform by N. The resultant panel clock will have two phases, wherein rate of phase change .DELTA.f is Nf.sub.c /2M. The spectral spacing .DELTA.f of sidebands around each har…
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.