Electrical transmission or interconnection systems – Anti-induction or coupling to other systems – Magnetic or electrostatic field control
Patent
1998-08-11
2000-12-26
Paladini, Albert W.
Electrical transmission or interconnection systems
Anti-induction or coupling to other systems
Magnetic or electrostatic field control
174250, 333247, 361748, 361763, 361794, H05K 116
Patent
active
06166457&
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a printed wiring board device for use in constructing electronic equipment, such as information equipment, and to electronic equipment, such as information equipment employing the printed wiring board device.
BACKGROUND ART
Unwanted electromagnetic radiation has been a problem encountered by various information apparatuses in recent years. Since the primary electromagnetic radiation has a frequency spectrum corresponding to that of harmonics generated by a clock on a printed wiring board, it has been considered that electromagnetic radiation is caused mainly by a signal line for transmitting a clock signal or a digital signal synchronous with the clock signal. Therefore, various electromagnetic radiation preventing measures have been taken to suppress electromagnetic radiation from signal lines formed on printed wiring boards and wire harnesses connected to those signal lines.
More specifically, those electromagnetic radiation preventing measures include (1) subjecting signals including clock signals and digital signals to low-pass filtering process to pass only signals of frequencies in a necessary band, (2) combining a damping resistor to an output signal line to increase the rise time and the fall time of signals and (3) forming a guard pattern of a ground potential near a signal line to form a small feedback current loop.
However, as is generally known, a frequency distribution of electromagnetic waves actually detected on a printed wiring board is different from a frequency distribution of electromagnetic waves estimated from a distribution of currents on signal lines, and the frequency distribution curve has a sharp peak for a specific frequency independently of the properties of the signal line. Therefore, it is expected that a main cause of electromagnetic radiation from a printed wiring board is not the signal lines but the electrical power system of the printed wiring board; that is, the main cause of electromagnetic radiation is the electrical resonance between the power source layer and the ground layer of the printed wiring board.
It is apparent that the foregoing conventional radiation preventing measures taken to suppress electromagnetic radiation from the signal lines of a printed wiring board and wire harnesses connected to those signal lines are ineffective in preventing electromagnetic radiation caused by the power source layer and the ground layer of the printed wiring board.
A method of suppressing electromagnetic radiation caused by the electrical power system of a printed wiring board, proposed in "Low-EMI Multilayer Printed-circuit Board", Kairo Jisso Gakkai Taikai Ronbun-shi, Vol. 10, p.175 uses a printed wiring board of a structure shown in FIG. 19.
In a printed wiring board for carrying out the method of suppressing electromagnetic radiation previously proposed in "Low-EMI Multilayer Printed-circuit Board", two ground layers 32A and 32B are formed on the opposite sides of a power source layer 31, respectively, resistors 33 are connected to end portions of the ground layers 32A and 32B so as to connect the ground layers 32A and 32B. Dielectric layers 34A and 34B of different dielectric constants are formed between the power source layer 31 and the ground layer 32A and between the power source layer 31 and the ground layer 32B, respectively, to suppress electrical resonance between the power source layer 31 and the ground layers 32A and 32B.
The structure of the printed wiring board shown in FIG. 19, which is fabricated by forming the two ground layers 32A and 32B on the opposite sides of the power source layer 31, respectively, connecting the resistors 33 to end portions of the ground layers 32A and 32B so as to connect the ground layers 32A and 32B, forming the dielectric layers 34A and 34B of different dielectric constants between the power source layer 31 and the ground layer 32A and between the power source layer 31 and the ground layer 32B, respectively, is greatly different from that of general printed wiring boards. Furth
REFERENCES:
patent: 4904988 (1990-02-01), Theus
patent: 5023753 (1991-06-01), Abe
patent: 5719750 (1998-02-01), Iwane
patent: 5926377 (1999-07-01), Nakao et al.
patent: 6002593 (1999-12-01), Tohya et al.
Iguchi Daisuke
Ueno Osamu
Fuji 'Xerox Co., Ltd.
Paladini Albert W.
LandOfFree
Printed-circuit assembly does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Printed-circuit assembly, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Printed-circuit assembly will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-998240