Electricity: measuring and testing – Impedance – admittance or other quantities representative of... – Parameter related to the reproduction or fidelity of a...
Reexamination Certificate
2002-06-18
2004-08-10
Chau, Minh (Department: 2854)
Electricity: measuring and testing
Impedance, admittance or other quantities representative of...
Parameter related to the reproduction or fidelity of a...
C361S782000, C716S030000, C716S030000
Reexamination Certificate
active
06774641
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a printed circuit board design support apparatus, method, and program and, more particularly, to a printed circuit board design support apparatus, method, and program which calculate the radiation amount of electromagnetic radiation from interconnections of a printed circuit board on the basis of printed circuit board design information related to the printed circuit board, components, and interconnections, thereby supporting design of a printed circuit board whose unwanted electromagnetic radiation is suppressed.
To prevent any adverse effect of unwanted electromagnetic waves radiated from electronic devices on public broadcastings or communications, it is necessary to suppress unwanted electromagnetic radiation from electronic devices and printed circuit boards mounted on the electronic devices. However, it is difficult to suppress electromagnetic radiation because causes thereof are hard to find. In some cases, to suppress electromagnetic radiation, a ferrite core is attached to the proximal end of the cable of a device, or a ferrite bead, a damping resistor, or various kinds of filters are inserted to a high-speed signal interconnection of a printed circuit board, resulting in an increase in cost of products. If even such measures are insufficient, boards are sometimes re-designed or re-manufactured. This delays shipping.
To suppress electromagnetic radiation without increasing the cost or delaying shipping, it is preferable to use a design method of suppressing electromagnetic radiation at the time of designing a printed circuit board. This is because the cost for correction can be suppressed at an upstream stage of design and development.
Under these circumstances, apparatuses for supporting design of a printed circuit board whose unwanted electromagnetic radiation is suppressed, design support methods, and storage media which store programs for supporting design have been conventionally proposed. Examples are “Printed Board CAD Apparatus” disclosed in Japanese Patent Laid-Open No. 5-67176, “Circuit Board Design Method and Storage Medium” disclosed in Japanese Patent Laid-Open No. 10-49568, and “Design Support Apparatus” disclosed in Japanese Patent Laid-Open No. 2001-134626.
FIG. 22
shows an embodiment of “Printed Board CAD Apparatus” disclosed in Japanese Patent Laid-Open No. 5-67176. In this prior art, a board surface is divided into a mesh pattern, and the current value of a signal path included in each divided mesh element is calculated. The visual attribute of the mesh is determined in accordance with the magnitude of the current value or a radiation noise predicted value for each mesh element, which is calculated on the basis of the current value. According to this prior art, the designer of a printed circuit board can intuitively understand the magnitude of the radiation noise amount on the basis of the magnitude of the current value or radiation noise predicted value indicated on the matrix. In addition, when the designer determines interconnections so as not to locally increase the indicator level, the noise amount on the board can be naturally dispersed.
FIG. 23
shows a flow chart of “Circuit Board Design Method and Storage Medium” disclosed in Japanese Patent Laid-Open No. 10-49568. In this prior art, in steps S
22
to S
24
, signal lines are virtually interconnected on a virtual section read out from a virtual section description table, and an unwanted radiation amount X is calculated. In step S
27
, for a signal interconnection whose unwanted radiation amount X exceeds an allowable value A, an improved solution N1 for an improved virtual section and an improved solution N2 with a target component inserted are calculated. In step S
28
, the improved solutions N1 and N2 are assigned to layer structures read out from a layer structure description table. In steps S
29
and S
30
, practical solutions P are extracted from combinations of the improved solutions N1 and N2 and the layer structures. An optimum solution Q is selected from the practical solutions P on the basis of the manufacturing cost and unwanted radiation amount. In step S
31
, the signal lines are automatically interconnected to a layer structure determined by the optimum solution Q. By this prior art, radiation noise can be evaluated and noise measures can be taken at an early stage of board design.
FIG. 24
shows the overall arrangement of “Design Support Apparatus” disclosed in Japanese Patent Laid-Open No. 2001-134626. As a characteristic feature, this prior art comprises a means (design data storage means
107
) for storing design information related to boards, components, and networks, a means (layout component selection means
110
) for selecting a component to be laid out, a means (high-speed network search means
111
) for searching the design data storage means for a high-speed network to be connected to the component to be laid out, a means (virtual interconnection path determination means
940
) for determining a virtual interconnection path of the high-speed network searched by the high-speed network search means, a means (radiation noise calculation means
950
) for calculating radiation noise of the high-speed network interconnected to the virtual interconnection path, and a means (radiation noise indicating information generation means
115
) for generating information that indicates radiation noise. According to this prior art, radiation noise simulation is done in laying out a component, and a radiation noise amount for the high-speed network connected to the component (layout component) to be laid out can be indicated to the designer in various indicating patterns. For this reason, an appropriate layout position of each layout component can be obtained, and interconnection design with a satisfactory radiation noise characteristic can be done.
In the above prior-art methods, as electromagnetic radiation from a printed circuit board, only electromagnetic radiation from signal interconnections (electromagnetic radiation called differential mode radiation or normal mode radiation) is handled.
In differential mode radiation, a closed circuit formed by signal interconnections acts like a loop antenna and emits electromagnetic radiation. As a general example, when a transmitting-side IC and receiving-side IC are connected by a microstrip line formed from an interconnection pattern and ground plane, a current flowing through the interconnection pattern and a mirror-image current of the interconnection pattern centered about the ground plane flow as a current of the closed loop. This causes radiation as in a loop antenna. Details are described in, e.g., IEICE TRAN. COMMUN., VOL. E78-B, NO. 2 February 1995, “Prediction of Peak Frequencies on Electromagnetic Emission from a Signal Line on a Printed Circuit Board”.
Electromagnetic radiation from a printed circuit board includes not only the radiation from a signal interconnection but also radiation from a ground plane opposing a signal interconnection (electromagnetic radiation called common mode radiation or asymmetrical mode radiation). For some boards, the common mode radiation is more dominant, as is reported. For example, reference 1 (R. Dockey, “Asymmetrical Mode Radiation from Multi-layer Printed Circuit Boards” EMC/ESD International Symposium, 1992, pp. 247-251) reports that a ground plane acts like a dipole antenna due to a current flowing through a signal interconnection, the entire ground plane causes resonance to induce strong electromagnetic radiation, and the radiation amount changes depending on the width of the ground plane.
Reference 2 (B. Archambeault, “Modeling of EMI Emissions from Microstrip Structures with Imperfect Reference Planes”, IEEE International Symposium on Electromagnetic Compatibility, Austin, 1997, pp. 456-461) reports that as the distance between a signal interconnection and an edge portion of a ground plane decreases, the electromagnetic radiation amount from a printed circuit board increases. These reports suggest that to design a printed ci
Eya Seishi
Harada Takashi
Kuriyama Toshihide
Sasaki Hideki
Wakui Akira
Chau Minh
NEC Corporation
Sughrue & Mion, PLLC
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