Computer-aided design and analysis of circuits and semiconductor – Nanotechnology related integrated circuit design
Reexamination Certificate
2001-02-28
2003-07-22
Smith, Matthew (Department: 2825)
Computer-aided design and analysis of circuits and semiconductor
Nanotechnology related integrated circuit design
Reexamination Certificate
active
06598208
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a design assisting method, a design assisting system, and a design assisting tool for use in designing printed-circuit boards or other electronic devices, and more particularly to a design assisting method and a design assisting system for designing electronic devices with reduced electromagnetic radiations.
2. Description of the Prior Art
It is necessary to design printed-circuit boards and electronic devices with reduced electromagnetic radiations in order to prevent any unwanted electromagnetic radiations from those printed-circuit boards and electronic devices from interfering the reception of broadcasts and communications and also from causing other electronic devices from malfunctioning. However, since it has been customary to design printed-circuit boards and electronic devices based on the experiences and know-hows of circuit designers, it has been difficult for anybody to design products incorporating effective countermeasures against unwanted electromagnetic radiations. In order to solve such a problem, there have been proposed various tools for assisting in designing printed-circuit boards and electronic devices with reduced electromagnetic radiations. For example, the proposals include Japanese laid-open patent application No. 10-049568 (JP, 10049568, A) and Japanese laid-open patent application No. 10-091663 (JP, 091663, A).
FIG. 1
is a flowchart illustrating the method for generating the layout of a printed-circuit board disclosed in JP, 10-049568, A. The disclosed method is based on the idea that the dominant radiation from a printed-circuit board originates from signal lines, and characterized by calculating the amount of radiation from signal lines, providing a countermeasure if the calculated amount of radiation exceeds a certain limit value, and determining an optimum layout for the countermeasure. The disclosed method allows a printed-circuit board to be designed with reduced electromagnetic radiations from the signal lines.
In step S
1
shown in
FIG. 1
, parts layout information indicative of the layout of parts and connection base information indicative of connections between the parts are determined using a conventional CAD (computer-aided design) system or a conventional circuit simulator. In step S
2
, board data as a basis for determining line constants for signal lines, such as conductor thicknesses, at the time circuits are formed on an actual board, and signal characteristics indicative of the characteristics of signals applied to the signal lines, such as device models representing input and output characteristics of the parts, are entered. A number 1 is set as an initial value for a table number m that is used for referring to a layer structure description table, and a number 1 is specified as an initial value for a cross-section number n in a hypothetical cross-section description table.
In step S
3
, hypothetical interconnection paths between the parts are calculated from the parts layout information and the connection base information both have been determined in step S
1
. In step S
4
, an amount X of unwanted radiation is calculated for each of the determined hypothetical interconnection paths. If the amount X of unwanted radiation is in excess of a preset allowable value A, then, in step S
5
, noise countermeasures are taken to reduce the amount X to or below the preset allowable value A. The noise countermeasures include two noise countermeasure procedures, i.e., a procedure of improving a hypothetical cross-section to strengthen the ground, and another procedure of inserting a noise countermeasure component such as a capacitor. In step S
6
, it is determined whether there is a signal line yet to be processed or not. If there is a signal line yet to be processed, then control goes back to step S
3
in order to repeat the processing in steps S
3
through S
5
for that signal line.
In step S
7
, with respect to all the signal lines whose amount X of unwanted radiation has exceeded the preset allowable value A, improved solution N
1
is calculated from the interconnection information with an improved cross-sectional shape, and improved solution N
2
is calculated from the interconnection information with an inserted noise countermeasure component. If improved solutions N
1
, N
2
are not particularly distinguished from each other, then they are simply referred to as improved solutions N.
After improved solutions N are determined in step S
7
, a description table and a described layer structure are assigned to each of improved solutions N. In step S
8
, it is then reviewed whether each of the layer structures can be practically feasible or not. In step S
9
, practically feasible solutions P are extracted from the combination of the layer structures and improved solutions N. Specifically, interconnection complexity levels &agr; and variations &ggr; of interconnection complexity levels &agr; are calculated with respect to the respective layer structures, and it is determined whether each of the layer structures is practically feasible or not based on whether or not interconnection complexity level &agr; and variation &ggr; thereof are equal to or smaller corresponding allowable values B, C. In step S
10
, optimum solution Q is selected from the collection of calculated practically feasible solutions P by evaluating sum x of amounts X of unwanted radiation and manufacturing cost y. Thereafter, in step S
11
, signal lines are actually placed on a layer structure determined by selected optimum solution Q. In this manner, interconnections on a printed-wiring board are determined.
FIG. 2
shows a conceptual presentation of operation of the CAD apparatus revealed in JP, 10091663, A. The disclosed CAD apparatus resides in that when a certain interconnection is specified on the CAD apparatus used for designing a printed-circuit board, an amount of radiation from the interconnection is calculated based on signal waveform information of the interconnection, and the intensity of radiation from place to place is visually displayed. The CAD apparatus is capable of identifying the position of a dominant signal interconnection which produces electromagnetic radiation, and hence permits a countermeasure to be easily taken against the radiation from the signal interconnection. The disclosure is characterized in that basic period T, voltage amplitude V
0
, rise and fall times t
r
, logic high period t
0
, and duty ratio &tgr; (=(t
r
−t
0
)/T) of the signal waveform can be described, and the printed-circuit board CAD apparatus calculates a current based on these descriptions. In
FIG. 2
, frames A
1
, A
2
, A
3
, A
4
, . . . schematically represent the concepts of these quantities and quantities derived therefrom. A trapezoidal signal shown in frame A
1
comprises a plurality of harmonics. When the circuit designer observes an n-th harmonic, if observed frequency f is f=n/T as indicated in frame A
2
, current I(f) can be calculated according to the equations in frames A
3
, A
4
.
If it is assumed that the interconnection layer is made of a metal foil having width &ohgr;, has interconnection length L, and one mesh used in calculations carried out by the CAD apparatus has area A, then a current density per mesh is expressed by I(f)·&ohgr;·L/A. The current density per mesh is calculated for each mesh, and each mesh is grouped into a level depending on the calculated current density, and displayed on the display screen of the CAD apparatus. As indicated by examples in frame A
6
, the levels are displayed in four or more luminance gradations, colors, or patterns.
In this manner, the CAD apparatus shown in
FIG. 2
appropriately displays the concentration of radiation noise in each area, allowing interconnections to be designed according to an interactive editing process.
Unwanted electromagnetic radiation will be described below.
In the technical field of unwanted electromagnetic radiation, high-frequency currents (or radio-frequency currents) are roughly divid
Harada Takashi
Kuriyama Toshihide
Sasaki Hideki
Do Thuan
NEC Corporation
Young & Thompson
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