Method and apparatus for reducing electromagnetic interference r

Details Method and apparatus for reducing electromagnetic interference r Method and apparatus for reducing electromagnetic interference r

1996-01-19

2000-02-01

Peng, John K.

Television

Video display

Cathode-ray tube

348819, 348820, 315 85, H04N 568

Patent

active

060209399

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.

REFERENCES:
patent: 5659399 (1997-08-01), Rindal et al.
patent: 5757338 (1998-05-01), Bassetti et al.

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