Method and apparatus to reduce peak electro-magnetic emissions f

Details Method and apparatus to reduce peak electro-magnetic emissions f Method and apparatus to reduce peak electro-magnetic emissions f

1998-12-18

2000-07-18

Jackson, Stephen W.

Electrical transmission or interconnection systems

Anti-induction or coupling to other systems

307407, 307409, H04B 328

Patent

active

060911654

ABSTRACT:
A method and an apparatus reduce peak electro-magnetic (EM) emissions from power and ground planes in, for example, a printed circuit board (PCB) by phase shifting synchronous signal sources to distribute EM emissions over a frequency range and by canceling at least some EM emissions with an inverse signal. According to one aspect of the present invention, two signal sources provide periodic outputs having the same period. The output of one of the signal sources, however, is delayed with respect to the output of the other signal source. Each signal source is coupled to a signal trace. The propagation delay over the signal trace coupled to the delayed signal source is shorter than the propagation delay over the other signal trace by the amount of the delay between the respective output signals. According to another aspect of the present invention, a noise cancellation driver is coupled to a signal source, a power or ground plane of the signal source, and an inverse voltage plane. The noise cancellation driver drives an inverse signal from the inverse voltage plane onto the power or ground plane when the signal source asserts a signal on the power or ground plane.

REFERENCES:
patent: 4419629 (1983-12-01), O'Brien
patent: 4769847 (1988-09-01), Taguchi
patent: 5264746 (1993-11-01), Ohmae et al.

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