Patent Publication Number: US-2016223598-A1

Title: Computing method and computing device

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is based upon and claims the benefit of priority of the prior Japanese Patent Application No. 2015-016015, filed on Jan. 29, 2015, the entire contents of which are incorporated herein by reference. 
     FIELD 
     The embodiments discussed herein are related to a computing method and a computing device. 
     BACKGROUND 
     Noise sources that produce radiation noise have been identified in printed circuit boards for use in electric appliances or the like. 
     Related art is disclosed in Japanese Laid-open Patent Publication No. 2009-123068 or Japanese Laid-open Patent Publication No. 2009-3790. 
     SUMMARY 
     According to an aspect of the embodiments, a computing method includes: detecting, in a circuit board, a coordinate of an area where a current greater than or equal to a threshold flows; extracting signal layer currents and GND layer currents within a given range based on the coordinate, the signal layer currents flowing in a signal layer and the GND layer currents flowing in a GND layer; computing, by a computer, a first current as a sum of the signal layer currents and a second current as a sum of the GND layer currents; and computing a third current as a sum of the first current and the second current in a section direction of the circuit board. 
     The object and advantages of the invention will be realized and attained by means of the elements and combinations particularly pointed out in the claims. 
     It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are not restrictive of the invention, as claimed. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  illustrates an example of a functional configuration of a computing device; 
         FIG. 2A  to  FIG. 2C  depict an example of data of current information; 
         FIG. 3  illustrates an example of a combined range; 
         FIG. 4  illustrates an example of a combined range; 
         FIG. 5  illustrates an example of a combined range; 
         FIG. 6  depicts an example of data of combined range information; 
         FIG. 7  illustrates an example of a detection process; 
         FIG. 8  illustrates an example of an extraction process; 
         FIG. 9  illustrates an example of a first computing process; 
         FIG. 10  illustrates an example of a second computing process; 
         FIG. 11  illustrates an example of combined currents in a match pattern; 
         FIG. 12  illustrates an example of a combined current at a circuit board end; 
         FIG. 13  illustrates an example of a combined current when there is a relatively short slit; 
         FIG. 14  illustrates an example of a combined current when there is a relatively long slit; 
         FIG. 15  illustrates an example of a combined current in a guard pattern case; 
         FIG. 16A  to  FIG. 16C  illustrate an example of distribution of current values in a match pattern case; 
         FIG. 17A  to  FIG. 17C  illustrate an example of distribution of current values when there is a slit; 
         FIG. 18A  to  FIG. 18C  illustrate an example of distribution of current values when a common mode current flows; 
         FIG. 19  illustrates an example of an anti-noise measures process; 
         FIG. 20  illustrates an example of a computing process; 
         FIG. 21A  to  FIG. 21C  illustrate an example of distribution of current values expressed in vectors; and 
         FIG. 22  illustrates an example of a computer. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     For example, an area where a current in a near electromagnetic field measured through an electromagnetic field simulation is large is considered to be a noise source, and thus the noise source may be identified. 
     It may be difficult to identify a noise source. For example, in a printed circuit board, when a current flows through a wiring line, a return current might occur. For example, if such a return current flows sufficiently close to a signal wiring line, radio waves cancel each other out and therefore the radiation level, which indicates the intensity of radiation, at a distant observation point is low. For example, if a return current flows on the ground or the like apart from the signal wiring line, radio waves do not cancel each other out and therefore the radiation level is high. For this reason, owing to the effect of a return current, an area where the current in a near electromagnetic field is large may not be a noise source for which there is a higher priority for measures to be taken. Therefore, according to the methods mentioned above, a noise source may not be identified. 
       FIG. 1  illustrates an example of a functional configuration of a computing device. A computing device  10  may be a device that carries out a simulation for identifying a noise source, which is a source at which radiation noise radiated from the circuit board is produced. For example, the computing device  10  may compute, through a simulation, a combined current as a sum of a current in a signal layer and a current in a GND layer of the circuit board in the section direction and, based on the computed combined current, may display noise source distribution. As illustrated in  FIG. 1 , the computing device  10  includes a communication interface (I/F) unit  30 , a storage unit  31 , a control unit  32 , an input unit  33 , and a display unit  34 . 
     The communication I/F unit  30  is an interface that controls communication with other devices. The communication I/F unit  30  transmits and receives various kinds of information via a network with other devices. For example, the communication I/F unit  30  receives information related to combined range information  41  and threshold information  42  from other devices. As the communication I/F unit  30 , a network interface card such as a local area network (LAN) card may be employed. The computing device  10  may obtain information such as the information related to the combined range information  41  and the threshold information  42  via a recording medium such as a memory card. The information related to the combined range information  41  and the threshold information  42  may be input from the input unit  33 . 
     The storage unit  31  may be a storage device, such as a semiconductor memory element such as a flash memory, a hard disk, or an optical disk. The storage unit  31  may be a data-rewritable semiconductor memory, such as a random access memory (RAM), a flash memory, or a non-volatile static random access memory (NVSRAM). 
     The storage unit  31  stores an operating system (OS) executed on the control unit  32  and various programs for processing received requests. The storage unit  31  stores various kinds of data used for programs executed on the control unit  32 . For example, the storage unit  31  stores current information  40 , the combined range information  41 , and the threshold information  42 . 
     The current information  40  may be data on a current on the circuit board obtained through an electromagnetic field simulation run by the simulation unit  51 . For example, in the current information  40 , coordinates representing positions on the circuit board and current values are stored in association with each other for each of the signal layer and the GND layer. 
       FIG. 2A  to  FIG. 2C  illustrate an example of data of current information. The current information  40  may be a table in which items of coordinates, a current value in the signal layer, a current value in the GND layer, and so on are associated with one another. The item of coordinates is an area storing coordinates representing positions on the circuit board. For example, in the item of coordinates, a combination of an X coordinate and a y coordinate representing a position on the circuit board is stored. The item of a current value in the signal layer is an area storing the current values of a current flowing in the signal layer among currents measured through an electromagnetic field simulation. For example, in the item of a current value in the signal layer, the current value of a current flowing in the signal layer at a position on the circuit board corresponding to coordinates is stored. The item of a current value in the GND layer is an area storing the current values of a current flowing in the GND layer among currents measured through the electromagnetic field simulation. For example, in the item of a current value in the GND layer, the current value of a current flowing in the GND layer at a position on the circuit board corresponding to coordinates is stored. 
     In  FIG. 2A  to  FIG. 2C , the current value in the signal layer is indicated as “9” at positions of coordinates (x2, y5) to (x8, y5). The current value in the signal layer is indicated as “0” at positions other than those of the coordinates (x2, y5) to (x8, y5). As a result, in the signal layer, a strong current flows at the positions of the coordinates (x2, y5) to (x8, y5) compared to the positions of other coordinates. 
     The current value in the GND layer is indicated as “−2” at positions of coordinates (x2, y4) to (x8, y4). The current value in the GND layer is indicated as “−1” at positions of coordinates (x1, y5) and (x9, y5). The current value in the GND layer is indicated as “−4” at positions of coordinates (x2, y5) and (x8, y5). The current value in the GND layer is “−5” at positions of coordinates (x3, y5) to (x7, y5). The current value in the GND layer is indicated as “−2” at positions of coordinates (x2, y6) to (x8, y6). The current value in the GND layer is indicated as “0” at positions other than those of the coordinates mentioned above. As a result, in the GND layer, a strong current flows at the positions of the coordinates (x2, y5) to (x8, y5) compared to positions of other coordinates. 
     In  FIG. 2A  to  FIG. 2C , the signs of current values in the signal layer and current values in the GND layer refer to directions in which the currents flow. As a result, in the example of  FIG. 2A  to  FIG. 2C , a current flowing in the GND layer flows in a direction opposite to that of a current flowing in the signal layer. 
     The combined range information  41  may be data indicating a range in which currents are combined. For example, the combined range information  41  stores values each indicating the length of a range for combining currents with the coordinates detected by the detection unit  52  as the center.  FIG. 3  illustrates an example of a combined range. In  FIG. 3 , an example where a signal current Tr 1  flows in the signal layer, a return current Re 1  flows in the GND layer, and the signal current Tr 1  is opposite in flow direction to the return current Re 1 . A width WR 1  of the return current Re 1  is wide compared to a width WT 1  of the signal current Tr 1  as illustrated in  FIG. 3 . For this reason, a combined current may be computed such that a spread of a return current is taken into account. For example, in order to accumulate a return current having a spread, a combined range indicating the range in which currents are combined is set. 
       FIG. 4  and  FIG. 5  illustrate examples of a combined range. In  FIG. 4 , a GND layer GL 1  is present just under a signal current TR 1  flowing in a signal layer TL 1 . In  FIG. 4 , the layer thickness, which is the distance between the signal layer TL 1  and the GND layer GL 1 , is “H”. In  FIG. 4 , a return current RE 1  flowing in the GND layer GL 1  has a spread with a width D from the center of the signal layer TL 1  in which the signal current TR 1  flows. In  FIG. 4 , the width D is less than 20 H, which is 20 times the layer thickness H. In such a case where the width D is less than 20 H, the radiation noise may not increase. 
     In  FIG. 5 , there is a portion where a slit SL is present just under a signal current TR 2  flowing in a signal layer TL 2  and where a GND layer GL 2  is absent. In  FIG. 5 , the layer thickness, which is the distance between the signal layer TL 2  and the GND layer GL 2 , is “H”. In  FIG. 5 , a return current RE 2  flowing in the GND layer GL 2  has a spread with a width of 20 H or more from the center of the signal layer TL 2  in which the signal current TR 2  flows. In such a case where the width of a return current is 20 H or more, the radiation noise may increase. Therefore, as a combined range, a value of 20 times the layer thickness may be set. 
       FIG. 6  depicts an example of data of combined range information. The combined range information  41  may be a table in which items of a layer thickness, a constant, a set value, and so on are associated with one another. The item of a layer thickness is an area storing the thickness of a layer between the signal layer and the GND layer of the circuit board. For example, the thickness of a layer between the signal layer and the GND layer detected from a layer definition file of a computer-aided design (CAD)-produced drawing or the like is stored in the layer thickness item. The item of a constant is an area storing a numeric value set in advance by the user. For example, in the item of a constant, an optimum numeric value representing the relationship between the layer thickness and the radiation noise obtained by an experiment or the like is stored. For example, in the item of a constant, since the width of a return current with which the radiation noise increases has a value of 20 times the layer thickness, “20” is stored. The item of a set value is an area storing the numeric value of a combined range representing a range where currents are combined. For example, in the item of a set value, a numeric value obtained by multiplying the layer thickness by a constant is stored. 
     In  FIG. 6 , the set value of the combined range may be “2 mm”, which is a value obtained by multiplying a thickness “100 μm” by a constant “20”. 
     The threshold information  42  is data serving as a criterion for determination of an area that is a possible noise source in the circuit board. For example, a threshold of the current value of a current flowing in the signal layer is stored in the threshold information  42 . For example, the threshold of the current value is set to an arbitrary value in accordance with a processing load on the computing device  10  caused by arithmetic processing of a combined current. 
     The input unit  33  illustrated in  FIG. 1  is an input device for inputting various kinds of information. As the input unit  33 , an input device, such as a mouse or a keyboard, that receives input of operations may be employed. For example, running operations for running an electromagnetic field simulation are input to the input unit  33  by the user. Information related to the combined range information  41  and the threshold information  42  is input to the input unit  33  by the user. For example, numeric values used for computation of a combined range and a numeric value serving as a threshold are input to the input unit  33 . 
     The display unit  34  may be a device, such as a liquid crystal display, that displays various kinds of information. For example, the display unit  34  displays various kinds of information in accordance with instructions of the output control unit  56 . For example, the display unit  34  displays noise source distribution generated by the output control unit  56 . For example, the display unit  34  displays distribution representing current values of a second combined current, as the noise source distribution. 
     The control unit  32  may be a device that controls the computing device  10 . As the control unit  32 , an electronic circuit such as a central processing unit (CPU) or a micro processing unit (MPU), or an integrated circuit such as an application specific integrated circuit (ASIC) or a field programmable gate array (FPGA) may be employed. The control unit  32  includes an internal memory for storing programs defining various processing procedures and control data and executes various processes based on the programs. The control unit  32  may function as various processing units when various programs are running. For example, the control unit  32  includes a receiving unit  50 , a simulation unit  51 , a detection unit  52 , an extraction unit  53 , a first computing unit  54 , a second computing unit  55 , and an output control unit  56 . 
     The receiving unit  50  may be a processing unit that receives various kinds of information. For example, the receiving unit  50  receives a running operation for run of an electromagnetic field simulation by the simulation unit  51 . The receiving unit  50  receives information related to the combined range information  41  and the threshold information  42  input through the input unit  33 . For example, the receiving unit  50  receives a numeric value used for computation of a combined range and stores the received numeric value in the item of a constant of the combined range information  41 . For example, the input unit  33  may receive a numeric value serving as a threshold and store the received numeric value in the threshold information  42 . 
     The simulation unit  51  runs an electromagnetic field simulation. For example, when a running operation is received by the receiving unit  50 , the simulation unit  51  computes the distribution of a current flowing in the signal layer and a current flowing in the GND layer of the circuit board. For example, the simulation unit  51  computes a current value in the signal layer and a current value in the GND layer for each coordinates on the circuit board. For example, the simulation unit  51  computes a current value in the signal layer and a current value in the GND layer by a finite-difference time-domain (FDTD) method. The simulation unit  51  stores the computed current values in the signal layer and in the GND layer in association with the coordinates in the current information  40 . 
     The detection unit  52  detects information on a possible noise source. For example, the coordinates of an area where a current greater than or equal to a threshold flows are detected in the circuit board. For example, the detection unit  52  obtains a threshold for current values stored in the threshold information  42 . The detection unit  52  obtains a current value in the signal layer for each coordinates stored in the current information  40 . The detection unit  52  detects the coordinates in the signal layer at which a current greater than or equal to the obtained threshold flows. 
       FIG. 7  illustrates an example of a detection process. In  FIG. 7 , an example where the signal current Tr 1  flows in the signal layer at a position of coordinates (X1, Y1) is illustrated. An example where the signal current Tr 2  flows in the signal layer at a position of coordinates (X2, Y1) is illustrated. An example where the return current Re 1  flows in the GND layer at the position of the coordinates (X1, Y1) is illustrated. An example where the return current Re 2  flows in the GND layer at the position of the coordinates (X2, Y1) is illustrated. The return current Re 1  flows in a direction opposite to that of the signal current Tr 1 . As a result, at the position of the coordinates (X1, Y1), the signal current Tr 1  and the return current Re 1  are normal mode currents that cancel each other out. The return current Re 2  flows in the same direction as that of the signal current Tr 2 . As a result, at the position of the coordinates (X2, Y1), the signal current Tr 2  and the return current Re 2  are common mode currents that do not cancel each other out and enhance each other. 
     The signal current Tr 1  and the signal current Tr 2  have current values greater than or equal to a threshold Th as illustrated in  FIG. 7 . For this reason, in  FIG. 7 , the detection unit  52  detects the coordinates (X1, Y1) and the coordinates (X2, Y1) as the coordinates of areas where currents greater than or equal to the threshold Th flow. 
     The extraction unit  53  illustrated in  FIG. 1  extracts current values in the signal layer and current values in the GND layer based on the coordinates detected by the detection unit  52 . For example, the extraction unit  53  extracts current values within a given range for each of the signal layer and the GND layer from the coordinates detected by the detection unit  52 . For example, the extraction unit  53  extracts current values within a combined range with the coordinates detected by the detection unit  52  as the center. 
       FIG. 8  illustrates an example of an extraction process. In  FIG. 8 , the extraction unit  53  extracts current values of the signal current Tr 1  within a combined range Cwt with the coordinates (X1, Y1) as the center. The extraction unit  53  extracts current values of the signal current Tr 2  within a combined range Cw 2  with the coordinates (X2, Y1) as the center. 
     The first computing unit  54  computes, for each layer, a first combined current resulting from combination in a current within a combined range. For example, the first computing unit  54  computes a first combined current as a sum of extracted current values for each of the signal layer and the GND layer. For example, the first computing unit  54  computes the current value of a first combined current in the signal layer by integrating extracted current values within the combined range in the signal layer. The first computing unit  54  computes the current value of a first combined current in the GND layer by integrating extracted current values within the combined range in the GND layer. 
       FIG. 9  illustrates an example of a first computing process. As illustrated in  FIG. 9 , the first computing unit  54  computes a first combined current CTr 1  in the signal layer resulting from integration of the signal current Tr 1  within the combined range Cwt in the signal layer illustrated in  FIG. 8 . The first computing unit  54  computes a first combined current CTr 2  in the signal layer resulting from integration of the signal current Tr 2  within the combined range Cw 2  in the signal layer illustrated in  FIG. 8 . The first computing unit  54  computes a first combined current CRe 1  in the GND layer resulting from integration of the return current Re 1  within the combined range Cwt in the GND layer illustrated in  FIG. 8 . The first computing unit  54  computes a first combined current CRe 2  in the GND layer resulting from integration of the return current Re 2  within the combined range Cw 2  in the GND layer illustrated in  FIG. 8 . 
     The second computing unit  55  computes a second combined current flowing in the section direction. For example, the second computing unit  55  computes the second combined current as a sum of the first combined current in the signal layer and the first combined current in the GND layer computed by the first computing unit  54  in the section direction. For example, the second computing unit  55  computes current values of the second combined current flowing in the section direction of the circuit board by adding current values in the section direction of the first combined current in the signal layer and current values in the section direction of the first combined current in the GND layer within the combined range. For example, the second computing unit  55  computes, for each position, a current value of the second combined current by adding the current value in the section direction of the first combined current in the signal layer and the current value in the section direction of the first combined current in the GND layer. 
       FIG. 10  illustrates an example of a second computing process. As illustrated in  FIG. 10 , the second computing unit  55  computes a second combined current Cs 1  as a sum of the first combined current CTr 1  in the signal layer and the first combined current CRe 1  in the GND layer illustrated in  FIG. 9  at each position within the combined range Cw 1 . The second computing unit  55  computes a second combined current Cs 2  as a sum of the first combined current CTr 2  in the signal layer and the first combined current CRe 2  in the GND layer illustrated in  FIG. 9  at each position within the combined range Cwt. In the example of  FIG. 10 , the second combined current Cs 1  has a low current value because the first combined current CTr 1  in the signal layer and the first combined current CRe 1  in the GND layer, which are currents flow in opposite directions, cancel each other out. The second combined current Cs 2  has a high current value because the first combined current CTr 2  in the signal layer and the first combined current CRe 2  in the GND layer, which are currents flowing in the same direction, do not cancel each other out but enhance each other. As a result, the second combined current Cs 2  has a high radiation level compared with the second combined current Cs 1 . Accordingly, an area where the signal current Tr 2  flows is highly likely to be a noise source compared with an area where the signal current Tr 1  flows. Taking measures for reducing noise for the area where the signal current Tr 2  flows may reduce noise effectively compared with the case in which measures are preferentially taken for an area where the signal current Tr 1  having a higher current value than that of the signal current Tr 2  flows. 
       FIG. 11  illustrates an example of combined currents in a match pattern. In  FIG. 11 , signal currents Tr 11  to Tr 13  flow in the signal layer. In  FIG. 11 , return currents Re 11  to Re 13  flow in the GND layer below wiring in the signal layer. The return currents Re 11  to Re 13  flow in a direction opposite to that of the signal currents Tr 11  to Tr 13 . In this case, the signal currents Tr 11  to Tr 13  and the return currents Re 11  to Re 13  cancel each other out within the combined range. As a result, second combined currents Cs 11  to Cs 13  flowing in the section direction of the circuit board have relatively low current values as illustrated in  FIG. 11 . Therefore, an area in the match pattern, which is relatively less affected by radiation, may not be a noise source. 
       FIG. 12  illustrates an example of a combined current at a circuit board end. In  FIG. 12 , signal currents Tr 21  to Tr 23  flow in the signal layer. In  FIG. 12 , return currents Re 21  to Re 23  flow in the GND layer below wiring in the signal layer. The signal current Tr 21  flows in the signal layer at an end of the circuit board. As a result, the return current Re 21  does not flow in a portion where the circuit board is absent, and a current value within the combined range is small compared with the return currents Re 22  to Re 23 . In this case, the return current Re 21  within the combined range that cancels the signal current Tr 21  is small in amount compared with the return currents Re 22  to Re 23 . As a result, a second combined current Cs 21  flowing in the section direction of the circuit board has a high current value compared with second combined currents Cs 22  to Cs 23  as illustrated in  FIG. 12 . Therefore, the end of the circuit board, which is relatively more affected by radiation, may be a noise source. 
       FIG. 13  illustrates an example of a combined current when there is a relatively short slit. In  FIG. 13 , a signal current Tr 31  flows in the signal layer. In  FIG. 13 , return currents Re 31  to Re 32  flow in the GND layer below wiring in the signal layer. Under the signal layer where the signal current Tr 31  flows, the GND layer having a relatively short slit SL 31  is located. As a result, a return current does not flow in an area with the slit SL 31  in the GND layer. However, in the vicinity of the slit SL 31 , the currents Re 31  to Re 32  in a direction opposite to that of the signal current Tr 31  flow. In this case, the signal current Tr 31  and the return currents Re 31  to Re 32  cancel each other out within the combined range. As a result, a second combined current Cs 31  flowing in the section direction of the circuit board has a relatively low current value as illustrated in  FIG. 13 . Accordingly, an area with a relatively short slit, which is relatively less affected by radiation, may not be a noise source. 
       FIG. 14  illustrates an example of combined currents when there is a relatively long slit. In  FIG. 14 , a signal current Tr 41  flows in the signal layer. In  FIG. 14 , return currents Re 41  to Re 42  flow in the GND layer below wiring in the signal layer. Under the signal layer where the signal current Tr 41  flows, the GND layer having a relatively long slit SL 41  is located. As a result, a return current does not flow in an area with the slit SL 41  in the GND layer. Currents Re 41  to Re 42  in a direction opposite to that of the signal current Tr 41  flow at positions apart from the center of the slit SL 41 . In this case, the signal current Tr 41  and the return currents Re 41  to Re 42  do not cancel each other out within the combined range. As a result, second combined currents Cs 41  to Cs 43  flowing in the section direction of the circuit board have high current values as illustrated in  FIG. 14 . Accordingly, an area with a relatively long slit, which is relatively more affected by radiation, may be a noise source. 
       FIG. 15  illustrates an example of a combined current in a guard pattern case. The guard pattern is a pattern in which a signal current and return currents flow in the same layer. In  FIG. 15 , a signal current Tr 51  flows in the signal layer. Return currents Re 51  to Re 52  flow in the signal layer. For example, in  FIG. 15 , the return currents Re 51  to Re 52  flow in the same layer as that of the signal current Tr 51 . The return currents Re 51  to Re 52  flow in a direction opposite to that of the signal current Tr 51 . In this case, the signal current Tr 51  and the return currents Re 51  to Re 52  cancel each other out within the combined range. As a result, a second combined current Cs 51  flowing in the section direction of the circuit board has a relatively low current value as illustrated in  FIG. 15 . Accordingly, the guard pattern, which is relatively less affected by radiation, may not be a noise source. 
     The output control unit  56  illustrated in  FIG. 1  outputs information on a noise source. For example, the output control unit  56  outputs noise source distribution indicating intensities of radiation noise radiated from the circuit board based on a second combined current computed by the second computing unit  55 . For example, the output control unit  56  outputs distribution of a current value as a sum of second combined currents in each given section on the circuit board. 
       FIG. 16A  to  FIG. 16C  illustrate an example of distribution of current values in a match pattern case. In  FIG. 16A , as distribution Tt 11 , a table associating “Coordinates” with “Current value in signal layer” depicted in  FIG. 2A  to  FIG. 2C  is illustrated. For example, the distribution Tt 11  indicates that the current value in the signal layer flowing at a position of coordinates (x1, y5) on the circuit board is “0”. For example, the distribution Tt 11  indicates that the current value in the signal layer flowing at a position of coordinates (x2, y5) on the circuit board is “9”. 
     In  FIG. 16A , as distribution Tg 11 , a table associating “Coordinates” with “Current value in GND layer” depicted in  FIG. 2A  to  FIG. 2C  is illustrated. For example, the distribution Tg 11  indicates that the current value in the GND layer flowing at the position of coordinates (x1, y5) on the circuit board is “−1”. For example, the distribution Tg 11  indicates that the current value in the GND layer flowing at the position of coordinates (x2, y5) on the circuit board is “−4”. In  FIG. 16A  to  FIG. 16C , the sign refers to the direction in which a current flows. In  FIG. 16A  to  FIG. 16C , the current flowing in the GND layer flows in a direction opposite to that of the current flowing in the signal layer. 
     In  FIG. 16B , distribution Tt 12  indicates the current value of a first combined current in the signal layer as a sum of current values in the signal layer in each given section on the circuit board. For example, the distribution Tt 12  indicates the current value of a first combined current in the signal layer as a sum of current values in the signal layer of each matrix of 3×3 cells in the distribution Tt 11  on the assumption that each coordinates indicated in the distribution Tt 11  are one cell. For example, a frame Ft 12  in the distribution Tt 12  indicates a current value “18” of a first combined current in the signal layer as a sum of current values in the signal layer of coordinates (x1, y4) to coordinates (x3, y6) included in a frame Ft 11  in the distribution Tt 11 . Similarly, distribution Tg 12  indicates the current value of a first combined current in the GND layer as a sum of current values in the GND layer of each matrix of 3×3 cells in the distribution Tg 11  on the assumption that each coordinates indicated in the distribution Tg 11  are one cell. For example, a frame Fg 12  in the distribution Tg 12  indicates a current value “−18” of a first combined current in the GND layer as a sum of current values in the GND layer of coordinates (x1, y4) to coordinates (x3, y6) of the distribution Tg 11 . 
     In  FIG. 16C , distribution Tb 11  indicates the current values of second combined currents as sums of current values of first combined currents in the signal layer and current values of first combined currents in the GND layer in the section direction of the circuit board. For example, a frame Fb 12  in the distribution Tb 11  indicates a current value “0” as a sum of a current value “18” indicated in the frame Ft 12  in the distribution Tt 12  and a current value “−18” indicated in the frame Fg 12  in the distribution Tg 12 , which is a position corresponding to the frame Ft 12 . As illustrated in  FIG. 16A  to  FIG. 16C , in the distribution Tb 11 , the first combined current in the signal layer and the first combined current in the GND layer cancel each other out in each of all the frames, and thus the second combined currents in all the frames are indicated to be “0”. The output control unit  56  displays, for example, the distribution Tb 11  on the display unit  34 . Since, in the match pattern illustrated in  FIG. 16A  to  FIG. 16C , the second combined currents in all the frames are “0”, the user may recognize that this match pattern, which is relatively less affected by radiation, is highly likely to be not a noise source. 
       FIG. 17A  to  FIG. 17C  illustrate an example of distribution of current values when there is a slit. In the example of  FIG. 17A , distribution Tt 21  indicates a table associating “Coordinates” on the circuit board with “Current value in signal layer” when there is a slit in the circuit board. In  FIG. 17A , distribution Tg 21  indicates a table associating “Coordinates” on the circuit board with “Current value in GND layer” when there is a slit in the circuit board. For example, there is a slit in the GND layer at positions of coordinates (x4, y3) to coordinates (x5, y7). As a result, the current values in the GND layer of coordinates (x4, y3) to coordinates (x5, y7) included in a frame Fg 11  of the distribution Tg 21  are “0”. 
     In  FIG. 17B , distribution Tt 22  indicates the current value of a first combined current in the signal layer as a sum of current values in the signal layer of each matrix of 3×3 cells in the distribution Tt 21  on the assumption that each coordinates indicated in the distribution Tt 21  are one cell. Distribution Tg 22  indicates the current value of a first combined current in the GND layer as a sum of current values in the GND layer of each matrix of 3×3 cells in the distribution Tg 21  on the assumption that coordinates indicated in the distribution Tg 21  are one cell. 
     In  FIG. 17C , distribution Tb 21  indicates the current values of second combined currents as sums of the current values of first combined currents in the signal layer indicated in the distribution Tt 22  and the current values of first combined currents in the GND layer indicated in the distribution Tg 22  in the section direction of the circuit board. As illustrated in  FIG. 17A  to  FIG. 17C , in the distribution Tb 21 , the current value indicated in a frame Fb 21  is highest. This indicates that the positions corresponding to the frame Fb 21  are relatively more affected by radiation. Accordingly, the distribution Tb 21 , in which the positions corresponding to the frame Fb 21  are highly likely to be a noise source, may be given high priority for anti-noise measures. 
       FIG. 18A  to  FIG. 18C  illustrate an example of distribution of current values when a common mode current flows. In  FIG. 18A , distribution Tt 31  indicates a table associating “Coordinates” on the circuit board with “Current value in signal layer” when the common mode current flows. In  FIG. 18B , distribution Tg 31  indicates a table associating “Coordinates” on the circuit board with “Current value in GND layer” when the common mode current flows. 
     In  FIG. 18B , distribution Tt 32  indicates the current value of a first combined current in the signal layer as a sum of current values in the signal layer of each matrix of 3×3 cells in the distribution Tt 31  on the assumption that each coordinates indicated in the distribution Tt 31  are one cell. Distribution Tg 32  indicates the current value of a first combined current in the GND layer as a sum of current values in the GND layer of each matrix of 3×3 cells in the distribution Tg 31  on the assumption that each coordinates indicated in the distribution Tg 31  are one cell. 
     In  FIG. 18C , distribution Tb 31  indicates the current values of second combined currents as sums of the current values of first combined currents in the signal layer indicated in the distribution Tt 32  and the current values of second combined currents in the GND layer indicated in the distribution Tg 32  in the section direction of the circuit board. As illustrated in  FIG. 18A  to  FIG. 18C , in the distribution Tb 31 , since the first combined currents in the signal layer included in a frame Ft 31  of the distribution Tt 32  and the first combined currents in the GND layer included in a frame Fg 31  of the distribution Tg 32  flow in the same direction and enhance each other, the current values indicated in a frame Fb 31  are relatively high. As a result, the distribution Tb 31  indicates that the positions corresponding to the frame Fb 31  are relatively more affected by radiation. Accordingly, the distribution Tb 31 , in which the positions corresponding to the frame Fb 31  are highly likely to be a noise source, may be given high priority for anti-noise measures. 
     The output control unit  56  displays, for example, the distribution Tb 11  to Tb 31  indicating such intensities of radiation noise on the display unit  34 . Therefore, referring to the distribution Tb 11  to Tb 31 , the user may recognize positions more affected by radiation in the circuit board and may recognize an area that is highly likely to be a noise source. The user takes anti-noise measures preferentially for an area that is highly likely to be a noise source, which may increase the efficiency of the measures. 
       FIG. 19  illustrates an example of an anti-noise measures process. The anti-noise measures process illustrated in  FIG. 19  may be executed by using the computing device  10  illustrated in  FIG. 1 . The anti-noise measures process illustrated in  FIG. 19  may be executed at a given time, for example at a time at which execution operations are received by the receiving unit  50  of the computing device  10 . 
     As illustrated in  FIG. 19 , the computing device  10  may carry out an electromagnetic field simulation for the current design pattern of the circuit board. For example, the computing device  10  carries out the electromagnetic field simulation for a design pattern before being subjected to anti-noise measures (S 100 ). For such a design pattern before being subjected to the anti-noise measures, the computing device  10  obtains the value of a current flowing in the signal layer and the value of a current flowing in the GND layer in a near electromagnetic field and the amount of radiation noise in a far electric field. The computing device  10  then stores the computed current value flowing in the signal layer and current value flowing in the GND layer in association with coordinates in the current information  40 . 
     The computing device  10  determines whether or not the amount of radiation noise in the far electric field is greater than a specification value (S 101 ). If the amount of radiation noise in the far electric field is less than or equal to the specification value (negative in S 101 ), then the computing device  10  completes the process. If the amount of radiation noise in the far electric field is greater than the specification value (affirmative in S 101 ), the computing device  10  executes a computing process (S 102 ). Thereby, the computing device  10  obtains noise source distribution. 
     The computing device  10  takes anti-noise measures based on the obtained noise source distribution (S 103 ). For example, the computing device  10  takes anti-noise measures for areas in order from the highest priority, based on the current values of second combined currents. For example, the computing device  10  takes anti-noise measures in order from an area with the highest current value of a second combined current. For example, the computing device  10  changes the design pattern by changing the shape of the GND layer, as anti-noise measures. For example, the computing device  10  changes the design pattern by arranging a capacitor in a slit portion of the GND pattern in order to cause a return current to flow close to the signal current, as anti-noise measures. For example, the computing device  10  changes the design pattern by arranging a resistor in order to convert current to heat, as anti-noise measures. 
     The computing device  10  carries out an electromagnetic field simulation for a design pattern after being subjected to the anti-noise measures (S 104 ). For such a design pattern after being subjected to the anti-noise measures, the computing device  10  obtains a current value flowing in the signal layer and a current value flowing in the GND layer in the near electromagnetic field and the amount of radiation noise in the far electric field. The computing device  10  stores the computed current value flowing in the signal layer and current value flowing in the GND layer in association with coordinates in the current information  40 . 
     The computing device  10  determines whether or not the amount of radiation noise in the far electric field is greater than a specification value (S 105 ). If the amount of radiation noise in the far electric field is less than or equal to the specification value (negative in S 105 ), then the computing device  10  completes the process. If the amount of radiation noise in the far electric field is greater than the specification value (affirmative in S 105 ), then the computing device  10  repeatedly performs the process in S 103  to S 105 . 
       FIG. 20  illustrates an example of a computing process. The computing process illustrated in  FIG. 20  may be executed by the computing device  10  illustrated in  FIG. 1 . As illustrated in  FIG. 20 , the computing device  10  sets a combined range in which currents are combined (S 200 ). For example, the computing device  10  stores “Layer thickness”, which is detected from a layer definition file of a CAD-produced drawing or the like, and “Constant”, which is received by the receiving unit  50 , in the combined range information  41 . The computing device  10  then sets, as a combined range, “Set value” obtained by multiplication of the “Layer thickness” and the “Constant” stored in the combined range information  41 . 
     The computing device  10  sets a threshold of a current value in the signal layer serving as a criterion for determining an area that is a possible noise source in the circuit board (S 201 ). For example, the computing device  10  stores a numeric value received as a threshold by the receiving unit  50  in the threshold information  42 , thereby setting the threshold of a current value. 
     The computing device  10  detects, in the circuit board, coordinates of an area where a current greater than or equal to the threshold flows (S 202 ). For example, the computing device  10  obtains the threshold of a current value stored in the threshold information  42 . The computing device  10  obtains the current value in the signal layer for each coordinates stored in the current information  40 . The computing device  10  detects the coordinates in the signal layer at which a current greater than or equal to the obtained threshold flows. 
     The computing device  10  extracts current values in a given range for each of the signal layer and the GND layer from the detected coordinates. For example, the computing device  10  obtains “Set value” as a combined range from the combined range information  41 . Using the “Set value” as the combined range, the computing device  10  extracts current values within the combined range with the detected coordinates as the center (S 203 ). 
     The computing device  10  computes the first combined currents for each of the layers (S 204 ). For example, the computing device  10  computes first combined currents as sums of the extracted current values for each of the signal layer and the GND layer. For example, the computing device  10  computes first combined currents in the signal layer by integrating the extracted current values within the combined range in the signal layer. The computing device  10  computes first combined currents in the GND layer by integrating the extracted current values within the combined range in the GND layer. 
     The computing device  10  computes second combined currents (S 205 ). For example, the computing device  10  computes second combined currents as sums of the computed first combined currents in the signal layer and first combined currents in the GND layer in the section direction. For example, the computing device  10  adds the current values in the section direction of the first combined currents in the signal layer and the current values in the section direction of the first combined currents in the GND layer together within the combined range, thereby computing the current values of second combined currents flowing in the section direction of the circuit board. 
     The computing device  10  displays noise source distribution based on the computed second combined currents (S 206 ) and completes the process. For example, the computing device  10  displays noise source distribution indicating intensities of radiation noise radiated from the circuit board based on the computed second combined currents. For example, the computing device  10  displays, as noise source distribution, distribution of current values as sums of second combined currents in each given section on the circuit board. 
     The computing device  10  detects, in the circuit board, the coordinates of an area where a current greater than or equal to a threshold flows. The computing device  10  extracts, from the detected coordinates, current values within a given range for each of the signal layer and the GND layer. The computing device  10  computes first combined currents as sums of the extracted current values for each of the signal layer and the GND layer. The computing device  10  computes second combined currents as sums of the computed first combined currents in the signal layer and first combined currents in the GND layer in the section direction. Thus, the computing device  10  recognize the intensities of radiation noise based on the second combined currents and therefore may identify a noise source. For example, the computing device  10  computes second combined currents and thus accurately identifies, for areas, the order of priority in which anti-noise measure are to be taken. This may reduce the number of times the electromagnetic field simulation is repeated. The computing device  10  takes anti-noise measures efficiently and thus may reduce time and energy of the user. 
     The computing device  10  outputs noise source distribution indicating the intensities of radiation noise radiated from the circuit board based on the computed second currents. As a result, with the computing device  10 , the user may recognize, in the circuit board, positions more affected by radiation. Therefore, an area that is highly likely to be a noise source may be easily recognized. With the computing device  10 , the measures are taken preferentially for an area that is highly likely to be a noise source, and thus the efficiency of the measures may be increased. 
     The computing device  10  outputs, as noise source distribution, distribution of current values as a sum of second currents in each given section on the circuit board. Therefore, the computing device  10  enables the positions more affected by radiation to be recognized in the circuit board using numeric values, and thus an area that is highly likely to be a noise source may be recognized more clearly. With the computing device  10 , the measures are taken more locally for an area that is highly likely to be a noise source, and thus the effect of the measures may increase. 
     The techniques described above may be carried out in various different forms. 
     For example, as noise source distribution, distribution of current values as a sum of second combined currents in each given section on the circuit board may be output. For example, the computing device  10  may output, as noise source distribution, distribution of current values represented by vectors. 
       FIG. 21A  to  FIG. 21C  illustrate an example of distribution of current values represented by vectors. In  FIG. 21A , distribution Dt indicates the current values represented by vectors of signal currents Tr 61  to Tr 64  flowing in the signal layer. In  FIG. 21B , distribution Dg indicates the current values represented by vectors of return currents Re 61  to Re 64  flowing in the GND layer. In  FIG. 21A  to  FIG. 21C , the directions of arrows refer to directions in which currents flow. The signal current Tr 61  and the return current Re 61  flow, in the circuit board, at a position P 1  of a match pattern. The signal current Tr 62  and the return current Re 62  flow, in the circuit board, at a position P 2  where there is a slit SL. The signal current Tr 63  and the return current Re 63  flow, in the circuit board, at a position P 3  where a common mode current flows. The signal current Tr 64  and the return current Re 64  flow, in the circuit board, at a position P 4  at a board end. 
     In  FIG. 21C , distribution Db indicates the current values represented by vectors of second combined currents Cs 61  to Cs 64  as sums of the signal currents Tr 61  to Tr 64  and the return currents Re 61  to Re 64  in the section direction of the circuit board. As illustrated in  FIG. 21C , the current value of the second combined current Cs 63  flowing, in the circuit board, at the position P 3  where a common mode current flows is largest compared with the second combined current Cs 61 , the second combined current Cs 62 , and the second combined current Cs 64 . As a result, in  FIG. 21A  to  FIG. 21C , the position P 3  where the second combined current Cs 63  flows is a noise source for which it is most preferable that the measures be taken. Preferentially taking anti-noise measures for the position P 3  may efficiently reduce noise. 
     The signal currents Tr 61  to Tr 64  have current values in order from the largest value to the smallest, the signal current Tr 62 , the signal current Tr 64 , and the signal current Tr 63 . As a result, when anti-noise measure are taken in order from the largest current value among the signal currents Tr 61  to Tr 64  flowing in the signal layer, not the second combined currents Cs 61  to Cs 64 , the measures are taken in the order of the position P 1 , the position P 2 , the position P 4 , and the position P 3 . In this case, there are three positions before the position  3  at which it is most preferable that anti-noise measures be taken. 
     When the measures are taken based on the current values of second combined currents, anti-noise measures are first taken for the position P 3 . As a result, when the measures are taken based on the current values of second combined currents, anti-noise measures may be taken more efficiently compared with the case where the measures are taken based on the current values of signal currents. For example, when the measures are taken based on the current values of second combined currents, the number of times where anti-noise measures are taken for the position P 3  is three smaller than in the case where the measures are taken based on the current values of signal currents. This may reduce time and energy of the user. 
     All the components of each of devices illustrated in the drawings may not be physically configured as illustrated in the drawings. For example, all or part of the distribution and integration of each device may be made as functional or physical distribution and integration in any units in accordance with various loads and usage situations. For example, processing units of the computing device  10  including the receiving unit  50 , the simulation unit  51 , the detection unit  52 , the extraction unit  53 , the first computing unit  54 , the second computing unit  55 , and the output control unit  56  may be suitably integrated. The processing of all the processing units may be suitably separated into the processing of a plurality of processing units. All or any part of all the processing functions performed in all the processing units may be implemented by a CPU or a program analyzed and executed on the CPU and may also be implemented as hardware by wired logic. 
     The various processes described above may be implemented when a program provided in advance is executed on a computer system such as a personal computer or a work station.  FIG. 22  illustrates an example of a computer system. The computer system illustrated in  FIG. 22  may execute a program having the functions described above, for example, a computing program. 
     As illustrated in  FIG. 22 , a computer  1300  includes a CPU  1310 , a hard disk drive (HDD)  1320 , and a random access memory (RAM)  1340 . These units  1300  to  1340  are coupled via a bus  1400 . 
     In the HDD  1320 , a computing program  1320   a  that exert functions similar to those of the receiving unit  50 , the simulation unit  51 , the detection unit  52 , the extraction unit  53 , the first computing unit  54 , the second computing unit  55 , and the output control unit  56  of the computing device  10  described above is stored in advance. The computing program  1320   a  may be suitably separated. 
     The HDD  1320  stores various kinds of information. For example, the HDD  1320  stores various kinds of data used for the OS and computing processes. 
     The CPU  1310  reads the computing program  1320   a  from the HDD  1320  and executes it, thereby executing operations similar to those of the processing units described above. For example, the computing program  1320   a  may perform operations similar to those of the receiving unit  50 , the simulation unit  51 , the detection unit  52 , the extraction unit  53 , the first computing unit  54 , the second computing unit  55 , and the output control unit  56  of the computing device  10 . 
     The computing program  1320   a  mentioned above does not have to be originally stored in the HDD  1320 . 
     For example, from a “portable physical medium”, such as a flexible disk (FD), a compact disk read-only memory (CD-ROM), a digital versatile disk (DVD), a magneto-optical disk, or an integrated circuit (IC) card, that is inserted into the computer  1300 , the computer  1300  may read a program and execute it. 
     “Another computer (or server)” or the like coupled to the computer  1300  via a public network, the Internet, a local area network (LAN), a wide area network (WAN), or the like may store a program, and the computer  1300  may read the program from it and execute the program. 
     All examples and conditional language recited herein are intended for pedagogical purposes to aid the reader in understanding the invention and the concepts contributed by the inventor to furthering the art, and are to be construed as being without limitation to such specifically recited examples and conditions, nor does the organization of such examples in the specification relate to a showing of the superiority and inferiority of the invention. Although the embodiments of the present invention have been described in detail, it should be understood that the various changes, substitutions, and alterations could be made hereto without departing from the spirit and scope of the invention.