Patent Application
20160253448
The present invention relates to a circuit board design system, a circuit board design method and a circuit board design program, all for designing a semiconductor circuit board. It particularly relates to a circuit board design system, a circuit board design method and a circuit board design program, all for designing a circuit board in consideration of electromagnetic field radiation generated from a cable which is connected to a circuit board mounted with semiconductor components.
Generally, when a semiconductor integrated circuit (hereafter, also described as an LSI) mounted on a printed circuit board (hereafter, also described as a PCB) is in operation, there arises a problem in that undesirable electromagnetic field radiation to outside is generated as a result of electric current flowing on the PCB being the noise source.
Such electromagnetic field radiation (hereafter, also described as undesirable electromagnetic field radiation or EMI (Electro Magnetic Interference)) becomes a cause of false operation of an electronic device itself in which the PCB is installed or other devices. For this reason, various measures against EMI are taken in electronic devices so as to reduce EMI to be equal to or lower than a predetermined permissible value. As one of such measures, it is requested to design in advance a PCB structure or an LSI layout in a manner to make EMI generated from the PCB to become at a low level.
Common mode radiation is mentioned as one of major elements of EMI generated from a PCB. When electric current flows in a wiring on a board, there occurs electromagnetic coupling between the wiring and a cable connected to the board, and as a result, there flows electric current referred to as common mode current even in the cable. The phenomenon of electromagnetic wave generation by the common mode current being a noise source and the cable working as an antenna is referred to as common mode radiation.
There is a tendency of the common mode radiation to increase, in association with the increase in the amount of current flowing in signal wirings on a PCB and in its flowing speed. Accordingly, in order to suppress the common mode radiation, it becomes necessary to take measures with respect to the PCB structure including its layer configuration, layout and the like, with respect to the characteristics of current flowing in the signal wirings and the length and connection position of the cable, and a measure of adding a countermeasure component, and the like. However, if design change or addition of a countermeasure component is performed after PCB production, for the purpose of suppressing EMI, there occurs a large increase in the design cost. To avoid that situation, it is important, from the aspect of low cost design of a PCB, to estimate the electrical characteristics at the design stage of the PCB and, according to the estimation result, take a measure for EMI suppression as necessary.
As a method for estimating common mode radiation to occur in advance at the PCB design stage, mentioned is a method of analyzing the electrical characteristics on the basis of information on such as the board structure, the structures of components to be mounted and that of a cable. As methods for analyzing the electrical characteristics, in particular, for analyzing electromagnetic field radiation, mentioned are electromagnetic field analysis methods such as a Finite Difference Time Domain (FDTD) method, a Method of Moments (MOM) and a Finite Element Method (FEM). These methods have been widely used in design of a printed circuit board. Accordingly, there has been employed is a PCB design method which performs electromagnetic field analysis of EMI generated from a PCB by the use of the above-described analysis methods, and then performs redesign according to the calculation result, with reference to the structure and specification of the PCB. Further, if a permissive condition of EMI is set in advance, it is possible, by comparing a result of the electromagnetic field analysis of EMI with the condition, to determine whether or not a design has been performed to make EMI generated from the board become at a low level.
A person having deep knowledge in relating fields such as of electrical circuits and electromagnetics, and further of a method of suppressing common mode radiation may have also knowledge of estimating in advance a candidate of an optimum cable connection position and about what kind of countermeasure means is to be used to enable suppression of common mode radiation. The number of necessary patterns to analyze may accordingly be relatively small, and furthermore, the person may have also knowledge about to what extent the accuracy can be decreased in creation of an analysis model without causing a problem. In that case, it may become possible to create a model whose analysis accuracy is secured even with a small analysis scale. However, it is difficult for a general user to perform the same way as such a person having deep knowledge as described above does. Therefore, as a design method, desired is a method which derives common mode radiation generated from a cable, from prepared design information on a PCB, in a short time and with high accuracy, and then automatically determines whether or not the radiation satisfies a permissive condition of EMI, or extracts an optimum design pattern.
In the PCB design stage, for predicting the amount of common mode radiation from a PCB to which a cable is connected, a method capable of calculating the characteristics including common mode current to flow in the cable in a short time and with sufficient analysis accuracy is required. Also required is an analytical design system which can be used by even a user not having deep knowledge of electrical circuits and electromagnetic waves, and enables the user to design a PCB of low EMI on the basis of the calculation results.
Patent Literature 1 (PTL 1) discloses an electromagnetic field strength calculation device which designs a PCB by means of an electromagnetic field analysis method (
As shown in
When creating a model for electromagnetic field analysis of a PCB, it is difficult to increase the analysis accuracy without modeling also a cable, connected to the PCB, which is considerably larger in size compared to the PCB.
Patent Literature 2 (PTL 2) discloses an electromagnetic field strength calculation device which transforms an electrical circuit device including a cable connected to it into an equivalent model, calculates common mode current flowing in the cable by an MOM, and calculates the strength of an electromagnetic field generated by the common mode current (
The electromagnetic field strength calculation device 201 of PTL 2 comprises an input means 202 for precisely inputting data on a structure of the electrical circuit device consisting of a printed board, a cable or the like, a lead or the like, and a metal housing or the like. The electromagnetic field strength calculation device 201 further comprises an electromagnetic field strength calculation means 203 which calculates the strength of an electromagnetic field radiated by the electrical circuit device on the basis of the inputted structure, and an output means 204 which outputs the calculation result. The electromagnetic field strength calculation means 203 has a partitioning means 210 which partitions the inputted structure into mesh elements. The electromagnetic field strength calculation means 203 further has a derivation means 211 which, on the basis of the partitioned structure, derives simultaneous equations of the MOM taking as unknown quantities an electric current flowing in each of metal portions of the electrical circuit device and equivalent electric and magnetic current flowing in a dielectric portion. The electromagnetic field strength calculation means 203 further has a calculation means 212 which calculates the unknown quantities by solving the simultaneous equations of the MOM derived as above, and a calculation means 213 which calculates from the calculated values the strength of an electromagnetic field radiated by the electrical circuit device. According to the electromagnetic field strength calculation device of PTL 2, as a result of considering also the strength of an electromagnetic field radiated by common mode current flowing in the metal portions other than that of the printed board, the strength of an electromagnetic field radiated by the electrical circuit device can be calculated with high accuracy.
[PTL 1] Japanese Patent Application Laid-Open No. H11-161690
[PTL 2] Japanese Patent Application Laid-Open No. H07-302278
As a method of deriving radiation from a printed circuit board by means of electromagnetic field analysis, there is one which calculates electromagnetic field radiation on the basis of common mode current flowing in a cable by modeling the whole of a system to be the subject of the analysis. However, the method has a problem in that, when calculating an electromagnetic field radiated from the whole system, the analysis space becomes considerably large because the length of a cable generally is considerably larger than the size of a printed board, and accordingly, a huge amount of calculation cost is required
In electromagnetic field analysis, an analysis space is partitioned into mesh elements, and then an electrical characteristic at each node of the mesh is derived. Therefore, the calculation cost can be reduced by reducing the number of partitioned mesh elements in the analysis space, that is, by increasing the mesh element size. However, because the calculation cost and the analysis accuracy are generally in a trade-off relationship, simply reducing the calculation cost causes decrease in the analysis accuracy, and accordingly makes it impossible to obtain a sufficiently guaranteed analysis result.
By applying the technology of PTL 2 into the technology of PTL 1, it becomes possible for even a person not having deep knowledge of electrical circuits and electromagnetic waves to create a model for electromagnetic field analysis from a PCB structure and accordingly perform quantitative calculation of EMI. However, when a cable connected to the PCB is directly modeled with no change, the analysis scale needs to be large in order to increase the analysis accuracy, which still raises the problem of a huge amount of calculation cost described above.
There is a case where, in an early stage of PCB design, analysis is performed of to which portion of the printed board a cable is to be connected to reduce common mode radiation. In that case, there are a plurality of candidates for a position at which the cable is connected to the printed board, and accordingly, if creating an analysis model and thereby performing electromagnetic field analysis for each of the connection position candidates, the analysis time comes to account for a large proportion of the design time. The analysis time for each of the patterns is desired to be short but, in order to reduce the analysis time for each of the models, the analysis scale for each of them needs to be reduced. Accordingly, even if the technology of PTL 2 is applied into the technology of PTL 1, there still is a problem in that the analysis accuracy decreases for each of the patterns when the scale of the analysis space is reduced.
The objective of the present invention is to provide a circuit board design system, a circuit board design method and a circuit board design program, all of which can solve the above-described problem.
A circuit board design system of the present invention is a circuit board design system for designing a circuit board with semiconductor components mounted on it and with a cable connected to it, the circuit board design system comprising: an input means which inputs board design information on a circuit board; an EMI characteristic derivation means which derives a characteristic of EMI generated from the circuit board, on the basis of the board design information; a storage means which stores a cable length correction characteristic for deriving the EMI characteristic; and an output means which outputs the EMI characteristic derived by the EMI characteristic derivation means, wherein the EMI characteristic derivation means comprises: an analysis model creation means which creates a simplified analysis model with a simplified virtual cable arranged in it, as an analysis model of the circuit board, on the basis of the board design information; a board analysis means which calculates virtual cable current flowing in the virtual cable by performing electromagnetic field analysis of the simplified analysis model; and an EMI calculation means which calculates actual cable current flowing in the cable by the use of the virtual cable current and the cable length correction characteristic, and then calculates a characteristic of EMI radiated from the cable by the use of the actual cable current.
A circuit board design method of the present invention is a circuit board design method for designing a circuit board with semiconductor components mounted on it and with a cable connected to it, the circuit board design method comprising: inputting board design information on a circuit board; creating a simplified analysis model with a simplified virtual cable arranged in it, as an analysis model of the circuit board, on the basis of the board design information; calculating virtual cable current flowing in the virtual cable by performing electromagnetic field analysis of the simplified analysis model; calculating actual cable current flowing in the cable by the use of the virtual cable current and a cable length correction characteristic for deriving an EMI characteristic; and calculating a characteristic of EMI radiated from the cable by the use of the actual cable current.
A circuit board design program of the present invention causes a computer, in a circuit board design system for designing a circuit board with semiconductor components mounted on it and with a cable connected to it, to execute steps of: inputting board design information on a circuit board; creating a simplified analysis model with a simplified virtual cable arranged in it, as an analysis model of the circuit board, on the basis of the board design information; calculating virtual cable current flowing in the virtual cable by performing electromagnetic field analysis of the simplified analysis model; calculating actual cable current flowing in the cable by the use of the virtual cable current and a cable length correction characteristic for deriving an EMI characteristic; and calculating a characteristic of EMI radiated from the cable by the use of the actual cable current.
According to the circuit board design system of the present invention, it becomes possible, in the design stage of a PCB with a cable connected to it, to design a PCB for which a characteristic of EMI generated from the cable is at a low level, in a short time and with high accuracy.
Hereinafter, exemplary embodiments of the present invention will be described using drawings. Here, in exemplary embodiments and a practical example described below, some restrictions which are technically preferable for implementation of the present invention will be made, but the present invention is not intended to be limited, in its scope, to the following exemplary embodiments and practical example.
First, a first exemplary embodiment for implementing the present invention will be described in detail, with reference to drawings.
(Configuration)
The circuit board design system of
The input means 1 is a means for inputting, into the EMI characteristic derivation means 2, input information including data such as structure information on a PCB with a cable connected to it and design information on components including an LSI mounted on the PCB.
Using the input information inputted from the input means 1, the EMI characteristic derivation means 2 derives a characteristic of EMI generated from the PCB with a cable connected to it. The EMI characteristic derivation means 2 comprises an analysis model creation means 4, a board analysis means 5 and an EMI calculation means 6.
The analysis model creation means 4 is a means for creating an analysis model of the PCB from the input information. The analysis model creation means 4 creates an electromagnetic field analysis model of the PCB (hereafter, also referred to as a “simplified board model”) where a cable having a virtual length (hereafter, also referred to as a “virtual cable”) is connected to the PCB, with the virtual length being sufficiently smaller than the length of the cable actually connected (hereafter, also referred to as an “actual cable”).
The board analysis means 5 is a means for performing electromagnetic field analysis by the use of the simplified board model created by the analysis model creation means 4, and it derives electric current flowing in the virtual cable (hereafter, also referred to as “virtual cable current”) by the electromagnetic field analysis.
The EMI calculation means 6 is a means for deriving a characteristic of electric current flowing in the actual cable (hereafter, also referred to as “actual cable current”), by the use of the virtual cable current derived by the board analysis means 5 and a characteristic corresponding to a relationship between the characteristic of the virtual cable current and that of the actual cable current (hereafter, also referred to as a “cable length correction characteristic”), and also calculating common mode radiation according to a relation between electric current and radiation. The EMI calculation means 6 also can derive an EMI characteristic equivalent to a characteristic of common mode radiation generated from the cable, with respect to the PCB structure included in the input information.
The database 3 is a storage means for storing the cable length correction characteristic. The system configuration is made such that the cable length correction characteristic stored in the database 3 is read out when the actual cable current is derived in the EMI calculation means 6.
The output means 7 is a means for outputting the EMI characteristic derived by the EMI characteristic derivation means 2. It may also output design information from which the EMI characteristic is obtained. It may further output data relating to the EMI characteristic derived by the EMI derivation means in a form of a graph or the like.
The above is the configuration of the circuit board design system according to the first exemplary embodiment of the present invention.
(Operation)
Here, features of operation of circuit board design systems according to exemplary embodiments of the present invention will be briefly summarized.
First, in order to derive an EMI characteristic corresponding to common mode radiation generated from a cable, an electromagnetic field analysis model is created by the use of board information and LSI information on a PCB and information on a cable. It is assumed that, in the analysis model, a cable connected to the board is a virtual cable having a virtual length which is sufficiently smaller than the length of the actual cable.
Then, electromagnetic field analysis is performed using the simplified board model in which the virtual cable is connected to the board, and thereby, virtual cable current is derived.
Further, setting in advance a cable length correction characteristic corresponding to a characteristic for correcting the virtual cable current into actual cable current to flow when the actual cable is connected, the actual cable current is derived from the virtual cable current and the cable length correction characteristic.
Then, using an equation for calculating common mode radiation from common mode current, common mode radiation generated from the cable by the effect of the actual cable current is calculated.
By the series of operations described above, an EMI characteristic of the PCB is derived.
The above is the most basic operation procedure of circuit board design systems according to exemplary embodiments of the present invention.
Hereinafter, a detail description will be given of a series of operations according to the first exemplary embodiment of the present invention, following a flow chart shown in
The flow chart of
Information to be inputted in the board design information input process of the step 11 is necessary information for deriving a characteristic of EMI generated from a PCB, which includes, for example, with respect to the PCB having a configuration with an LSI and other components mounted on and a cable connected to the board, the physical structure of the board including its layout and layer structure, that of the cable, information on the mounted LSI and other components, and the like. Hereafter, such pieces of information are totally referred to as board design information. The board design information is inputted by the input means 1 of
Next, the analysis model creation means 4 comprised in the EMI characteristic derivation means 2 of
In the simplified board model creation process of the step 12, the analysis model creation means 4 creates a simplified board model in which the PCB structure except for the cable is reflected and a virtual cable is connected as an alternative cable.
Next, the board analysis means 5 comprised in the EMI characteristic derivation means 2 of
In the a virtual cable current derivation process of the step 13, the board analysis means 5 derives virtual cable current flowing in the virtual cable.
Next, the EMI calculation means 6 comprised in the EMI characteristic derivation means 2 of
In the cable length corrected EMI characteristic calculation process of the step 14, the EMI calculation means 6 reads out the cable length correction characteristic stored in the database 3 of
Then, the EMI characteristic derivation means 2 performs a result output process where it outputs the common mode radiation characteristic derived in the step 14 to the output means 7 of
The series of processes described above is the procedure according to the first exemplary embodiment.
Here, a length of the virtual cable to be connected in the simplified board model may be automatically obtained by a following equation 1, where the maximum frequency of the analysis is represented by Fc and the maximum value for the length of the virtual cable by Lc1.
L
c1=300×106/(4×Fc) (1)
The equation 1 is usually expressed in the form of an inequality expressing that the left side is equal to or smaller than the right side, and in that case, the equation 1 expresses that the maximum value for the length of the virtual cable is equal to or smaller than ¼ of the wavelength λc of the maximum analysis frequency Fc. When the cable length is equal to ¼ of the wavelength, a resonance component appears in the cable current. Considering that, by setting the virtual cable length at a value equal to or smaller than ¼ of the smallest wavelength corresponding to the maximum frequency in the analysis range, it becomes possible to obtain a virtual cable current including no resonance component due to the cable length.
When the virtual cable length is too small, the length becomes little different from the size in thickness direction of the board model, and accordingly, highly accurate reproduction of an actual cable current from the virtual cable current becomes difficult. In that regard, when the virtual cable length equals to about ¼ of the wavelength, highly accurate reproduction of an actual cable current from the virtual cable current becomes possible, because the virtual cable length is sufficiently larger than the size in thickness direction of the board model.
Here, as a specific example, a description will be given of an example of the first exemplary embodiment where the input information is set to be the board information on a PCB having a configuration with LSIs and other components mounted on and a cable connected to the board in a manner expressed by a layout in the horizontal plane shown in
In
When the wiring current 24 flows in the signal wiring 23, there occurs electromagnetic coupling between the signal wiring 23 and the cable 27, and accordingly, a cable current 28 flows in the cable 27.
As a result, EMI 29 corresponding to common mode radiation is generated, with the cable current 28 and the cable 27 being the generating source and the antenna, respectively.
Here, EMI 29 is generated also from the signal wiring 23 and wirings within the LSIs 21 and 22, and from between a power supply and GND of the PCB 20, which are not illustrated in the diagram. However, because the cable current 28 is common mode current with no return path, the common mode radiation generated from the cable 27 is predominant among the whole kinds of radiation in the system. Accordingly, in the present specific example, an EMI characteristic will be described as that obtained by taking only the common mode radiation generated from the cable 27 into consideration.
Operation of the specific example will be described, following the flow chart of
First, in the board design information input process of
Next, using the inputted board design information, the analysis model creation means 4 of
Here, it is assumed that a system performing electromagnetic field analysis by the use of an FDTD method as a means for analyzing the simplified board model is employed. In that case, from the above-described board design information on the PCB 20, an electromagnetic field analysis model of a three-dimensional (hereafter, also described as “3D”) structure shown in
In the electromagnetic field analysis model of
A transmission-side parameter 41 is a parameter obtained by extracting only necessary part for the analysis from the structure and electrical characteristics of the transmission-side LSI 21. A reception-side parameter 42 is a parameter obtained by extracting only necessary part for the analysis from the structure and electrical characteristics of the reception-side LSI 22. A wiring parameter 43 is a parameter obtained by extracting 3D structure information on and electrical characteristics of the signal wiring 23. A board portion parameter 44 is a parameter obtained by extracting necessary information from the layer configuration 35, corresponding to the thickness and electrical characteristics of each layer. A component parameter 45 is a parameter obtained by extracting only necessary part for the analysis from the structure and characteristics of the mounting component 25. A connector parameter 46 is a parameter obtained by extracting only necessary part for the analysis from the structure and characteristics of the connector 26. A cable parameter 47 is a parameter including the structure and electrical characteristics of the cable and the structure and characteristics of a component connected to the cable. A via parameter 48 is a parameter obtained by extracting 3D structure information on and electrical characteristics of the via 34.
Here, if a model is created using the actual cable length in the cable parameter 47, the model turns out to be that shown in
In
Because a model created in the present specific example is a simplified board model in which a virtual cable model 56 is connected, as shown in
At the present stage, the board analysis means 5 of
Next, the EMI calculation means 6 of
Here, a description will be given of details of the cable length corrected EMI characteristic calculation process of the step 14.
First, the EMI calculation means 6 reads out a cable length correction characteristic rc stored in the database 3 of
The characteristic of the actual cable current Ic is derived, for example, by multiplying the characteristic of the virtual cable current Ic1 by the cable length correction characteristic rc, as shown in
Next, using thus calculated actual cable current Ic, the EMI calculation means 6 derives an EMI characteristic 60 corresponding to a characteristic of common mode radiation generated from the cable model 52. As an equation for the derivation, one described in Non-Patent Literature 1 (NPL 1: Shigeo Suzuki, “Comprehensible introduction to practical noise countermeasures in analog/digital mixed circuits”, Nikkan Kogyo Shimbun, 2007) can be used. NPL 1 describes that, expressing the frequency of the virtual cable current Ic1 by F, its cable length by L, and the distance of a position from the cable by D, the common mode radiation field strength Ecm at the position can be calculated by a following equation 2.
Ecm=1.257×10−6×Ic1×F×L/D (2)
Next, the EMI characteristic corresponding to common mode radiation from the cable 27 is outputted by the output process 7 of
By using the series of processes, it becomes possible to accurately derive an EMI characteristic with respect to such a PCB configuration as shown in
Thus, the detail description of the first exemplary embodiment has been given above, using the specific example. Here, the above-described specific example is just an example, and any other examples obtained by making various changes to the configuration and operation of the above-described specific example also should be included within the scope of the present invention.
If using an electromagnetic field analysis model of the PCB where the actual cable is directly modeled with no change (hereafter, also referred to as a “detailed board model”), the analysis scale becomes considerably large, because the length of the cable is a dominant cause of the increase in the analysis space. In contrast, in the case of using the simplified board model described in the first exemplary embodiment of the present invention, the length of the virtual cable is substantially smaller than the actual cable length, and accordingly, the analysis space can be diminished, and the analysis scale is decreased by that amount.
Further, in the case of using the simplified board model described in the first exemplary embodiment of the present invention, it is not necessary to intentionally decrease the number of mesh elements because the analysis space naturally becomes small, and accordingly, a virtual cable current can be derived in a shorter time with no decrease in the analysis accuracy.
That is, by the above-described series of operations according to the first exemplary embodiment of the present invention, it is possible to derive common mode radiation in a shorter time than when performing the analysis using the detailed board model. Additionally, if the cable correction characteristic is set with high accuracy, the derivation of common mode radiation can be performed with no decrease in the analysis accuracy.
Further, according to the circuit board design system of the present invention, in the design stage of a PCB with a cable connected to it, it becomes possible for even a person not having deep knowledge of electrical circuits and electromagnetic waves to design a PCB making a characteristic of EMI (common mode radiation) generated from the cable become at a low level, in a short time and with high accuracy.
As the EMI characteristic derivation means for deriving EMI generated from a PCB, in particular, common mode radiation generated from a cable, by the use of design information on the PCB, for example, a general electromagnetic field analysis tool or system can be used.
What needs to be set as input information to that kind of EMI characteristic derivation means includes CAD (Computer Aided Design) data including the external structure of the PCB and information on its connection with a component and a connector, a data sheet showing the operation and structure of a mounted LSI, a data sheet for a mounted component, and the like. These kinds of data are those which generally can be obtained by a designer at an early PCB design stage. There also exists an input tool or system which enables to create an analysis model by inputting those kinds of information into an analysis tool, and it also can be employed as an input means.
Further, by providing a program reflecting the above-described series of processes, it becomes possible for even a person not having deep knowledge of electrical circuits and electromagnetic waves to design a PCB configuration having a low level EMI characteristic, in a short time and with high accuracy.
Next, a second exemplary embodiment of the present invention will be described in detail, with reference to drawings.
(Configuration)
The EMI characteristic determination means 8 is a means which compares an EMI characteristic derived by the EMI characteristic derivation means 2 with an EMI permissive condition stored in the database 3 as a condition for permitting an EMI characteristic, and thereby determines whether the derived EMI characteristic satisfies the EMI permissive condition or not.
Accordingly, the system configuration is made such that, to the output means 7, not only the derived EMI characteristic but also the result of determining whether or not the inputted PCB configuration satisfies the EMI permissive condition are outputted.
(Operation)
Hereinafter, the series of processes according to the second exemplary embodiment will be described, following the flow chart of
First, the input means 1 performs the board design information input process where it inputs board design information on a PCB into the EMI characteristic derivation means 2 of
Next, the analysis model creation means 4 in the EMI characteristic derivation means 2 of
Then, the board analysis means 5 in the EMI characteristic derivation means of
Next, the EMI calculation means 6 in the EMI characteristic derivation means 2 of
In the cable length corrected EMI characteristic calculation process of the step 24, the EMI calculation means 6 firstly reads out a cable length correction characteristic stored in the database 3 of
The above-described steps 21 to 24 according to the second exemplary embodiment, shown in
Subsequently to those steps, the EMI characteristic determination means 8 of
In the EMI characteristic determination process of the step 25, the EMI characteristic determination means 8 reads out an EMI permissive condition stored in the database 3 of
Then, the EMI characteristics determination means 8 performs a result output process where it outputs, to the output means 7 of
The series of processes described above is the one according to the second exemplary embodiment.
Here, an example of comparison performed by the EMI determination means is shown in
In the example shown in the left diagram of
In contrast, in the example shown in the right diagram of
As a result of such determination, what is outputted to the output means 7 of
By outputting such a comparison result as shown in
Thus, as in the second exemplary embodiment, it is possible to set in advance an EMI permissive condition and add a process of determining whether a derived EMI characteristic satisfies the EMI permissive condition or not. By adding the process to the series of processes according to the first exemplary embodiment already described, it becomes possible to automatically determine whether or not a PCB has been designed in a manner to satisfy an EMI permissive condition.
Further, according to the second exemplary embodiment of the present invention, it is possible to derive in a short time a characteristic of common mode radiation generated from a PCB with a cable connected to it, and thereby perform determination with respect to an EMI permissive condition corresponding to a condition for permitting EMI generated from the cable in a short time. As a result, it becomes possible to determine whether or not a PCB has been designed to have a structure and specifications making the characteristic of EMI generated from the PCB become at a low level, and accordingly, design of a PCB structure satisfying a permissive EMI value can be performed easily.
Further, because an EMI characteristic derived in the second exemplary embodiment of the present invention is a quantitative value, it also becomes possible to determine what amount of margin against an EMI permissive condition remains for a designed PCB structure. Therefore, by changing a characteristic of the EMI permissive condition if necessary, a PCB structure or PCB specifications with a larger amount of margin can be designed.
Next, a third exemplary embodiment of the present invention will be described in detail, with reference to drawings.
(Configuration)
The third exemplary embodiment is configured such that, when no cable length correction characteristic is stored in the database 3, a cable length correction characteristic can be derived by the cable length correction characteristic derivation means 9, from an analysis result obtained by the analysis model generation means 4 and the board analysis means 5, and can be fed back to the database 3. The cable length correction characteristic created by the cable length correction characteristic derivation means 9 is stored in the database 3, and can be read out later when other board design information is inputted. The system according to the third exemplary embodiment is also configured such that an EMI characteristic derived at an intermediate stage during derivation of the cable length correction characteristic and a determination result obtained by the EMI characteristic determination means 8 can be outputted to the output means 7.
(Operation)
First, the input means 1 performs the board design information input process where it inputs board design information on a PCB into the EMI characteristic derivation means 2B of
Next, using the inputted board design information, the analysis model creation means 4, board analysis means 5 and the cable length correction characteristics derivation means 9, of
In the present step, the detailed board model shown in
Next, the analysis model creation means 4 of
Next, the board analysis means 5 of
Next, the EMI calculation means 6 of
Then, the EMI characteristic determination means 8 of
In the EMI characteristic determination process of the step 36, the EMI characteristic determination means 8 reads out an EMI permissive condition stored in the database 3 of
Subsequently, the EMI characteristics determination means 8 performs the result output process where it outputs, to the output means 7 of
The series of processes described above is the process flow according to the third exemplary embodiment. Here, it is assumed that a step 38 shown in
According to the series of processes, even if no cable length correction characteristic is stored in advance in the database 3, a cable length correction characteristic can be derived from actual board design information at an early stage of the process flow. Then, thus derived cable length correction characteristic can be used when an EMI characteristic is to be derived from different board design information.
First, the analysis model creation means 4 of
The detailed board model creation process of the step 301 is a process of creating the detailed board model shown in
Next, the board analysis means 5 of
In the actual cable current derivation process of the step 302, the board analysis means 5 derives the actual cable current 54 by performing electromagnetic field analysis of the detailed board model shown in
Next, the analysis model creation means 4 of
Then, the board analysis means 5 of
In the virtual cable current derivation process of the step 304, the board analysis means 5 derives the virtual cable current 58 by performing electromagnetic field analysis of the simplified board model shown in
Next, the cable length correction characteristic derivation means 9 of
In the cable length correction characteristic calculation process of the step 305, the cable length correction characteristic derivation means 9 derives a cable length correction characteristic from the actual cable current 54 and the virtual cable current 58. Referring to the graphs shown in
Next, the cable length correction characteristic derivation means 9 of
In the database output process of the step 306, the cable length correction characteristic derivation means 9 outputs the derived cable length correction characteristic to the database 3 of
According to the third exemplary embodiment of the present invention, a cable length correction characteristic having been derived from a piece of actual board design information on a PCB can be used also when deriving an EMI characteristic of the PCB by the use of different board design information. As a result, when a plurality of pieces of board design information are set, a final result can be obtained by the present method in a shorter time than a method which performs, with respect to each and every one of the plurality of pieces of board design information, creation of a detailed model, direct derivation of an EMI characteristic from the model, and determination of whether or not the EMI characteristic satisfies an EMI permissive condition. This advantage of the present exemplary embodiment increases with increase in the number of patterns of board design information, on a PCB, for each of which derivation of an EMI characteristic and subsequent determination of whether or not it satisfies an EMI permissive condition is required to be performed.
According to the third exemplary embodiment of the present invention, the calculation using a virtual cable current and a cable length correction characteristic can be automatically performed by employing, for example, a method which derives a characteristic approximating the product of the virtual cable current and the cable length correction characteristic. As a result, common mode radiation generated from actual cable current can be derived by using the equation as it is, and accordingly, common mode radiation can be derived from virtual cable current automatically and in a short time.
Further, according to the third exemplary embodiment of the present invention, it is also possible, when no cable length correction characteristic is set in advance, to derive a cable length correction characteristic from results of analyses using, respectively, a detailed board model and a simplified board model. Specifically, it is possible to employ, for example, a method which calculates a current ratio from an actual cable current characteristic and a virtual cable current characteristic derived by the use of the respectively corresponding analysis models. Thus obtained cable length correction characteristic can be used as it is, in a case of performing the series of processes according to the third exemplary embodiment after the design condition is changed such as by changing a position for cable connection. Even in that case, common mode radiation can be derived in a shorter time than a method which performs, with respect to each and every position for cable connection, creation of a detailed board model, analysis of the model and subsequent derivation of common mode radiation.
Next, a fourth exemplary embodiment of the present invention will be described in detail, with reference to drawings.
(Configuration)
The storage device 10 is a storage means which stores the database 3, board design information including PCB design information 11 corresponding to information on a PCB's structure and components, LSI design information 12 corresponding to information on an LSI's structure and characteristics, cable structure design information 13 corresponding to a cable's physical structure, and the like.
The board design information is automatically inputted from the storage device 10 to the EMI characteristic derivation means 2B, through operation of the input means 1. The system configuration is made such that, from the inputted board design information and a cable length correction characteristic and an EMI permissive condition from the database 3, an EMI characteristic is automatically derived, and then a result of determining whether or not the EMI characteristic satisfies the EMI permissive condition is outputted. Further, the EMI characteristic determination means 8 is configured such that it not only outputs the determination result of whether or not the EMI characteristic satisfies the EMI permissive condition to the output means 7, but also reflects the output result into the board design information (PCB design information 11, LSI design information 12 and cable structure design information 13).
Examples of information included in the PCB design information 11 are that on the sizes of planes and wirings of the board, that on connection positions and characteristics of the components, and that on the cable connection, which are typically given as two-dimensional CAD data. The PCB design information 11 also includes information on the layer structure of the board shown in
As examples of information included in the LSI design information 12, mentioned are, as information on the transmission-side LSI 21 of
As examples of information included in the cable structure design information 13, mentioned are information on the cable structure such as the length or the diameter, that on the electrical characteristics of the cable, that on connection at the terminal on the opposite side of the cable, and the like.
(Operation)
A series of processes according to the fourth exemplary embodiment of the present invention follows the flow chart shown in
First, the input means 1 performs the board design information input process where it inputs the board design information on a PCB stored in the storage device 10 of
It may be defined that, in the board design information input process of the step 31, for example, at the same time when the PCB design information 11 being such as CAD data on the board (circuit board design information) is inputted, information on components mounted on the board also is inputted. It may be further defined that, at the same time, the LSI design information 12 corresponding to information on an LSI to be mounted (semiconductor integrated circuit design information) and the cable structure design information 13 corresponding to information on a cable to be connected are inputted.
Next, the analysis model creation means 4, the board analysis means 5 and the cable length correction characteristic derivation means 9, of
In the cable length correction characteristic derivation process of the step 32, the board generation means consisting of the analysis model creation means 4 and the board analysis means 5 creates the detailed board model (
Next, the board analysis means 5 of
Next, the board analysis means 5 of
Next, the EMI calculation means 6 of
Then, the EMI characteristic determination means 8 of
In the EMI characteristic determination process of the step 36, the EMI characteristic determination means 8 reads out an EMI permissive condition stored in the database 3 of the storage device 10 in
Subsequently, the EMI characteristic determination means 8 performs the result output process where it outputs, to the output means 7 of
With that, the series of operations according to the fourth exemplary embodiment is completed. Here, a board design information update process may be performed simultaneously and in parallel with the step 37 (step 38).
In the board design information update process of the step 38, the board design information in the storage device 10 (PCB design information 11, LSI design information 12 and cable structure design information 13) is updated in a manner to reflect the EMI characteristic and the EMI permissive condition. For example, the result of determining whether the set EMI permissive condition is satisfied or not may be reflected into the board design information in the storage device 10. When the EMI permissive condition is not satisfied, for example, a process which records an error into the CAD data and simultaneously outputs a result of comparison with the EMI permissive condition, like that shown in the left diagram of
Thus, in the fourth exemplary embodiment, the PCB design information 11, the LSI design information 12 and the cable structure design information 13, which are included in the set board design information, are simultaneously inputted. On the basis of the board design information, an EMI characteristic is derived, and then a result of determining whether or not the derived EMI characteristic satisfies an EMI permissive condition is outputted. As a result, it is possible for even a person not having deep knowledge of electrical circuits and electromagnetic waves to cause the system to perform the series of processes, if the person can at least set board design information into the storage device 10. It consequently becomes possible to easily design a PCB structure and PCB specifications making common mode radiation generated from a cable become at a low level.
In a system into which the fourth exemplary embodiment of the present invention is reflected, structure information on a PCB, design information on components mounted on the PCB, including LSIs, and structure information on a cable are set as input information. By causing a computer to execute the series of processes by the use of the input information, it becomes possible to design a PCB structure and PCB specifications making common mode radiation generated from a cable become at a low level. Such operation can be performed easily by even a person not having deep knowledge of electrical circuits and electromagnetic waves.
Further, according to the fourth exemplary embodiment, a cable length correction characteristic can be calculated by means of electromagnetic field analysis, contrarily to in the preceding exemplary embodiments. Accordingly, it is also possible to derive a cable length correction characteristic in performing the procedure on a certain pattern and then apply the derived cable length correction characteristic also to a plurality of different patterns. As a result, it becomes possible to derive an EMI characteristic with respect to each of the plurality of patterns with high accuracy and in a shorter time.
As has been described above, in the fourth exemplary embodiment of the present invention, design information including a structure, specifications and the like of a PCB, an EMI permissive condition and a cable length correction characteristic are set in advance. Accordingly, the system according to the fourth exemplary embodiment makes it possible for even a person not having deep knowledge of electrical circuits and electromagnetic waves to automatically determine whether or not a characteristic of EMI generated from the PCB is at a low level and also automatically design an optimum structure.
Next, a fifth exemplary embodiment of the present invention will be described in detail, with reference to drawings.
(Configuration)
In the fifth exemplary embodiment of the present invention, the system configuration shown in
(Operation)
First, the input means 1 performs the board design information input process where it inputs the board design information on a PCB stored in the storage device 10 of
It may be defined that, in the board design information input process of the step 41, with respect to the structure of the PCB 20 in
Next, the EMI characteristic derivation means 2B of
In the initial cable connection position determination process of the step 42, the EMI characteristic derivation means 2B determines a position at which the cable is connected first, from among the cable connection position candidates 30 of
Next, the analysis model creation means 4, the board analysis means 5 and the cable length correction characteristic derivation means 9, of
In the cable length correction characteristic derivation process of the step 43, the board generation means consisting of the analysis model creation means 4 and the board analysis means 5 creates a detailed board model (
Next, the EMI characteristic derivation means 2B of
The cable connection position selection process of the step 44 is a process of selecting a cable connection position with respect to which a common mode radiation characteristic is to be calculated, and at the present stage, the initial cable connection position is selected without substitution.
Next, the board analysis means 5 of
Next, the board analysis means 5 of
Next, the EMI calculation means 6 of
Then, the EMI characteristic derivation means 2B of
Next, the EMI characteristic derivation means 2B of
Here, the present description will be continued for the case where the derivation of common mode radiation characteristics with respect to all of the cable connection positions has not yet been completed (No at the Step 49). In that case, that is, if the step 49 results in No, returning to the cable connection position selection process of the step 44, the EMI characteristic derivation means 2B performs a process of selecting a cable connection position with respect to which a common mode radiation characteristic is to be derived next. A method of determining the cable connection position may be set already in the board design information, and in particular, it is preferable that the method is included in the PCB design information 11. For example, the method may be set to be such as that which selects one of the cable connection position candidates 30 of
Next, the board analysis means 5 of
Next, the board analysis means 5 of
Next, the EMI calculation means 6 of
Then, the EMI characteristic derivation means 2B of
Next, the EMI characteristic derivation means 2B of
If, even at the present stage, the derivation of common mode radiation characteristics with respect to all of the cable connection position candidates 30 has not yet been completed, returning to the cable connection position selection process of the step 44, the procedure of selecting a cable connection position with respect to which a common mode radiation characteristic is to be derived next, and then deriving a common mode radiation characteristic for when the cable is connected at the selected position is repeated.
The above is the operation flow of when the derivation of common mode radiation characteristics with respect to all of the cable connection positions has not yet been completed (No at the step 49).
On the other hand, if it is determined, in the cable connection position completion determination process of the step 49, that a common mode radiation characteristic has been derived with respect to each and every one of the cable connection position candidates 30 shown in
In the EMI characteristic determination process of the step 50, the EMI characteristic determination means 8 reads out an EMI permissive condition stored in the database 3 of the storage device 10 in
Then, the EMI characteristic determination means 8 performs the result output process where it outputs, to the output means 7 of
With that process, the series of operations according to the fifth exemplary embodiment is completed. Here, a board design information update process (step 52) may be performed simultaneously and in parallel with the step 51.
In the board design information update process of the step 52, the board design information in the storage device 10 (PCB design information 11, LSI design information 12 and cable structure design information 13) is updated in a manner to reflect the EMI characteristics and the EMI permissive condition. For example, the results of determining whether or not the set EMI permissive condition is satisfied with respect to respective ones of the cable connection position candidates 30 can be reflected into the board design information set in the storage device 10. As a way of the reflection, it may be defined that an error sign is recorded into the CAD data for any of the cable connection position candidates 30 which does not satisfy the EMI permissive condition, or the like. Alternatively, a process of outputting a result of comparison with the EMI permissive condition, like that shown in
Thus, in the fifth exemplary embodiment, the PCB design information 11, the LSI design information 12 and the cable structure design information 13, which are included in the set board design information, are simultaneously inputted, and on the basis of those pieces of information, an EMI characteristic is derived with respect to each cable connection position candidate, and then a result of determining whether or not each of the derived EMI characteristics satisfies an EMI permissive condition is outputted. As a result, what needs to be done by a user becomes only to cause the system to perform the series of processes if the user can at least set the board design information into the storage device 10, and accordingly, it becomes possible for the user to easily find a cable connection position making common mode radiation generated from the cable become at a low level, and to design a PCB structure and PCB specifications on the basis of the finding result. Further, because derivation of an EMI characteristic with respect to a single piece of input information can be performed in a short time, it becomes possible, even when a plurality of patterns need to be analyzed, to derive EMI characteristics with respect to all of the patterns in a realistic time. The above-described user operation can be easily dealt with by even a person not having deep knowledge of electrical circuits and electromagnetic waves.
Next, a sixth exemplary embodiment of the present invention will be described in detail, with reference to drawings.
(Configuration)
(Operation)
First, the input means 1 performs the board design information input process where it inputs board design information on a PCB into the EMI characteristic derivation means 2 of
Next, the analysis model creation means 4 in the EMI characteristic derivation means 2 of
Then, on the basis of the simplified board model (
Next, the EMI calculation means 6 in the EMI characteristic derivation means 2 of
In the cable length corrected EMI characteristic calculation process of the step 64, the EMI calculation means 6 reads out a cable length correction characteristic stored in the database 3 of
Then, the EMI characteristic determination means 8 of
In the EMI characteristic determination process of the step 65, the EMI characteristic determination means 8 reads out an EMI permissive condition stored in the database 3 of
Next, the EMI characteristic determination means 8 of
In the change determination process of the step 66, according to the result of determining whether or not the EMI permissive condition is satisfied, the EMI characteristic determination means 8 selects whether or not to perform the board configuration change process on the PCB.
Here, when the derived common mode radiation characteristic does not satisfy the EMI permissive condition (No at the step 66), the board configuration change means 14 of
The board configuration change process of the step 68 will be described below.
First, in the EMI characteristic determination process of the step 65, at the same time when the board configuration change means 14 calls for an EMI permissive condition from the database 3, it also calls for a guideline on changing a PCB configuration to be performed when the EMI permissive condition is not satisfied. Then, in accordance with the guideline on change, the board configuration change means 14 performs a process of changing the PCB design information 11, the LSI design information 12 and the cable structure design information 13, which have been prepared as the board design information on the PCB. With respect to the board design information based on the changed PCB configuration, the board configuration change means 14 performs again the series of processes starting from the step 61 of
When, in the change determination process of the step 66, the derived common mode radiation characteristic satisfies the EMI permissive condition (Yes at the step 66), the EMI characteristic determination means 8 performs the result output process where it outputs the determination result to the output means 7 (Step 67). Here, the determination result corresponds to an EMI characteristic equivalent to the derived common mode radiation characteristic and whether or not the EMI characteristic satisfies the EMI permissive condition.
With that process, the series of processes according to the sixth exemplary embodiment is completed. Here, it is assumed that steps 69, 70 and 71 of
At the present stage of the processes, if the board design information has been changed, the changed board design information may be outputted simultaneously and in parallel with the step 67. At the same time, diagrams comparing the EMI permissive condition with the EMI characteristics obtained respectively before and after the change of board design information may be also outputted. For example, a comparison diagram for the case of not satisfying the EMI permissive condition before the change of board design information, like that in the left diagram of
Further, a plurality of guidelines on changing a board configuration may be set. When the EMI permissive condition has not been satisfied by one change of board design information, if next change guidelines had been set, it becomes possible to obtain a PCB configuration satisfying the EMI permissive condition by repeating change of the board configuration. For example, the guidelines may be set to be such as that instructs to change also the LSI design information 12 if the EMI permissive condition is not satisfied even by changing the PCB design information 11, and to change also the cable structure design information 13 if the EMI permissive condition is not satisfied even by changing the LSI design information 12. The orders of changing the prepared board design information may be combined optionally.
Thus, in the present exemplary embodiment, what needs to be done by a user is to cause the system to perform the series of processes if the user has set board design information, an EMI permissive condition and a guideline(s) on changing the board configuration, and as a result, it becomes possible to easily design a PCB structure and PCB specifications making common mode radiation generated from the cable become at a low level.
Next, a seventh exemplary embodiment of the present invention will be described in detail, with reference to drawings.
(Configuration)
The storage device 10 stores, similarly to in the fourth exemplary embodiment, the database 3 and board design information including the PCB design information 11 corresponding to information on a PCB's structure and components, the LSI design information 12 corresponding to information on an LSI's structure and characteristics, and the cable structure design information 13 corresponding to a cable's physical structure.
In the seventh exemplary embodiment, the input means 1 automatically inputs the board design information from the storage device 10 to the EMI characteristic derivation means 2. From the inputted board design information and a cable length correction characteristic and an EMI permissive condition obtained from the database 3, the EMI characteristic determination means 8 automatically performs derivation of an EMI characteristic and determination of whether the derived EMI characteristic satisfies the EMI permissive condition or not. Here, the system configuration is made such that, if the EMI characteristic determination means 8 determines that the inputted PCB configuration does not satisfy the EMI permissive condition, the board configuration change means 14 changes the board configuration, according to a guideline on changing the PCB configuration set in advance. In accordance with the configuration change, the board configuration change means 14 changes the board design information on the PCB and inputs the changed board design information again to the EMI characteristic derivation means 2. The guideline on changing the PCB configuration may be set in advance in the database 3, and may also be set such that the EMI characteristic determination means 8 can call for the guideline on change at the same time when it calls for the EMI permissive condition from the database 3. Further, the system configuration is made such that the derived EMI characteristic and PCB configuration information for a case of satisfying the EMI permissive condition is not only outputted to the output means 7, but the outputted result is also reflected into the board design information (PCB design information 11, LSI design information 12 and cable structure design information 13).
(Operation)
In the seventh exemplary embodiment, a series of processes is performed according to the flow chart of
First, the input means 1 performs the board design information input process where it inputs the PCB design information 11 into the EMI characteristic derivation means 2 of
In the board design information input process of the step 61, at the same time when the PCB design information 11 including such as CAD data on a board is inputted, information on components mounted on the board may also be inputted. Also at the same time, the LSI design information 12 corresponding to information on LSIs mounted on the board and the cable structure design information 13 corresponding to information on a cable connected to the board may be inputted.
Next, the board analysis means 5 of
Then, using the simplified board model (
Next, using the virtual cable current 58, the EMI calculation means 6 in the EMI characteristic derivation means 2 of
In the cable length corrected EMI characteristic calculation process of the step 64, the EMI calculation means 6 reads out the cable length correction characteristic stored in the database 3 of
Subsequently, the EMI characteristic determination means 8 of
In the EMI characteristic determination process of the step 65, the EMI characteristic determination means 8 reads out the EMI permissive condition stored in the database 3 of
Next, the EMI characteristic determination means 8 of
In the change determination process of the step 66, according to the determination result derived in the step 65, the EMI characteristic determination means 8 selects whether or not to perform the board configuration change process on the PCB.
Here, when the derived common mode radiation characteristic does not satisfy the EMI permissive condition (No at the step 66), the board configuration change means 14 of
The board configuration change process of the step 68 will be described below.
First, in the EMI characteristic determination process of the step 65, at the same time when the board configuration change means 14 calls for the EMI permissive condition from the database 3, it also calls for a guideline on changing the PCB configuration to be performed when the EMI permissive condition is not satisfied.
Accordingly, following the guideline on change, the board configuration change means 14 performs a process of changing the board design information on the PCB, in such a manner as shown in
On the other hand, when, in the change determination process of the step 66, the derived common mode radiation characteristic satisfies the EMI permissive condition (Yes at the step 66), the result output process is performed. In the result output process, the EMI characteristic determination means 8 outputs, to the output means 7 of
With that process, the series of processes according to the seventh exemplary embodiment is completed.
At the present stage of the processes, if the board design information has been changed, the changed board design information and diagrams comparing the EMI permissive condition with the EMI characteristics obtained respectively before and after the change of board design information may be outputted simultaneously and in parallel with the step 67. Further, the board design information in the storage device 10 may be updated at the same time, in accordance with the change of board design information.
Specifically, if the PCB design information 11 has been changed, a PCB design information update process is performed, where the PCB design information 11 in the storage device 10 of
The above is the description of the series of processes according to the seventh exemplary embodiment.
(Example of Board Design Information Change)
Here, a description will be given of an example of changing board design information in the steps 69 to 71 according to the seventh exemplary embodiment, using
In contrast, in the case of the example shown in the right diagram of
In the above-described case, as updated information to be included into the PCB design information 11, mentioned are the change in the layer for the signal wiring (when the wiring is partially changed into an internal layer wiring, the corresponding part only), the change in the three-dimensional structure due to the change of layers, and addition and position change of a via associated with the change of the wiring partially into an internal layer wiring. Those pieces of updated information are written into the PCB design information 11 in the PCB design information update process of the step 69 in
In an example for before changing the configuration (the left diagram in
In
In this example of change, the cable 27 before the change shown in the left diagram in
In the above-described case, as a change of the cable structure design information 13, mentioned is that in the material and diameter of the cable 90 caused by the ferrite coating. The updated information is written into the cable structure design information 13 in the cable structure design information update process of the step 71 in
The above is the description of the steps 69 to 71 of
As has been described above, in the seventh exemplary embodiment, the PCB design information 11, the LSI design information 12 and the cable structure design information 13, which are included in the board design information set in advance, are simultaneously inputted. Then, the board design information is changed on the basis of a guideline on change, in a manner to obtain an EMI characteristic satisfying an EMI permissive condition, and the changed board design information is outputted. Accordingly, if it is possible at least to set the board design information and a guideline on change for when the EMI permissive condition is not satisfied, to the storage device 10, then the series of processes are performed by the system, and a PCB configuration satisfying the EMI permissive condition is outputted. As a result, it becomes possible for even a person not having deep knowledge of electrical circuits and electromagnetic waves to easily design a PCB structure and PCB specifications making common mode radiation generated from the cable become at a low level.
In the circuit board design system according to the seventh exemplary embodiment, what needs to be done by a user is only to set a plurality of patterns of PCB design information and then cause the system to perform the series of processes on the basis of input information with respect to each of the patterns. Accordingly, it becomes possible for the user to easily design a PCB structure and PCB specifications making common mode radiation generated from the cable become at a low level. The above-described user operation can be easily dealt with by even a person not having deep knowledge of electrical circuits and electromagnetic waves.
Further, according to the seventh exemplary embodiment, when PCB design information having a plurality of different patterns has been set, by repeatedly performing the series of processes described above with respect to each of the patterns, it becomes possible to automatically determine which one of the design patterns satisfies an EMI permissive condition, and thereby extract an optimum design pattern. Also in that case, because the determination on a single pattern can be performed in a short time, it becomes possible to extract an optimum pattern in a realistic design time.
Here, as a practical example according to one of the exemplary embodiments of the present invention (the fifth exemplary embodiment), an example of designing a PCB configuration will be described.
(Configuration)
The board 65 has a set of conductor layers 66 in a form of a six-layer structure. The set of conductor layers 66 held by the board 65 is arranged in a manner to line up the constituent layers as S-G-S-V-G-S in order from the surface layer (the first layer). Here, S represents a signal layer, G a ground layer (also referred to as a GND layer), and V a power supply layer (voltage layer, also referred to as a VCC layer). It is defined that the constituent layers of the set of conductor layers 66 are called, in order from the surface layer, respectively, first signal layer 66-1, first GND layer 66-2, second signal layer 66-3, VCC layer 66-4, second GND layer 66-5 and third signal layer 66-6. A dielectric material with a relative dielectric constant ∈ r=4.2 is present between each of the layers. A number shown at the right side of each of the layers in
The transmission-side and reception-side LSIs not illustrated in the diagram and the signal wiring are all arranged on or in the first S layer 66-1 being the top layer. The transmission-side and reception-side LSIs are each connected to one of the GND layers and the VCC layer through vias not illustrated in the diagram.
Cable connectors (with a size of 5 mm×5 mm) are also provided on the top layer, and they are each connected to one of the GND layers through a via not illustrated in the diagram. As selectable cable connectors, the cable connection position candidates A, B and C are set. The cable connection position candidate A is located at a position which abuts on the left end of the board and is 20 mm away from the bottom end (64A in
The GND layers (both of the two layers) and the VCC layer each have a full plane structure and the same lateral size as that of the board. The third and sixth layers are set to be signal layers, but in the present pattern, they exist only as constituent layers of the six-layer board and accordingly are not in use. The above-described information is included in the PCB design information 11 of
In the LSI design information 12 of
While the cable connection position has not been determined yet, structure information that the material of the cable is copper, its diameter is 1 mm and its length is 1 m is included in the cable structure connection information 13 of
Here, assuming that an EMI permissive condition “a characteristic of EMI to be generated should be equal to or lower than 65 μV/m over a frequency range up to 500 MHz” is set, performed is determination, with respect to the above-described PCB, of selecting which cable connection position from among the cable connection position candidates A, B and C enables to design a PCB structure satisfying the EMI permissive condition, by the use of the system according to the fifth exemplary embodiment. There, it is assumed that no cable length correction characteristic is set in the initial stage.
(Operation)
A series of processes in the present practical example will be described below. The series of processes in the present practical example is performed following the flow chart of
First, the PCB design information 11, the LSI design information 12 and the cable structure design information 13 corresponding to board design information on the PCB shown in
The board design information input process of
Next, the initial cable connection position determination process of
Next, the cable length correction characteristic derivation process of
The cable length correction characteristic derivation process of the step 43 will be described below, using
First, by performing the detailed board model creation process of the step 301 in
In creating the detailed board model of
Next, the board analysis means 5 of
Here, the actual cable current 70 derived as above shows a characteristic represented by a dashed line in
Next, by performing the simplified board model creation process of the step 303 in
There, because there should be no difference in the board model between the detailed and simplified board models, the board model used in the detailed board model creation process of the step 301 in
L
c1=300×106/(4×500×106)=150×10−3 (3)
Here, in consideration of the accuracy, the virtual cable length is set at 150 mm, which is the maximum value Lc1 calculated as above. This condition may be set in advance in the cable structure connection information 13, or the system may be configured such that the virtual cable length Lc1 is automatically determined if reading the cable structure connection information, and then the virtual cable model 71 is created to have the virtual cable length Lc1.
In the present stage, an analysis space 72 is formed in relation to the virtual cable model 71, as shown in
Next, the board analysis means 5 of
A characteristic of the virtual cable current 73 becomes that represented by a solid line in
Next, the cable length correction characteristic derivation means 9 of
The method for deriving a cable length correction characteristic may be installed in advance into the cable length correction characteristic derivation means 9, where it may be installed in a manner to enable its customization when change in the cable length occurs. Information about a cable length correction characteristic may be included in the cable structure connection information 13 and automatically selected when the cable structure connection information 13 is inputted.
Next, the database output process of the step 306 in
The above-described processes of the steps 301 to 306 in
Next, the EMI characteristic derivation means 2B of
In the process flow according to the fifth exemplary embodiment, it is usual that, next, the board analysis means 5 of
In the process flow according to the fifth exemplary embodiment, it is usual that, next, the board analysis means 5 of
Next, the EMI calculation means 6 of
At the present stage, the EMI calculation means 6 has already derived the actual cable current 70 for when the cable connection position is the cable connection position candidate A in the cable length correction characteristic derivation process of the step 43 in
According to
Next, the EMI characteristic derivation means 2B of
Next, the EMI characteristic derivation means 2B of
At the present stage, because the derivation has been performed only with respect to the cable connection position candidate A, which is the initial design position, returning to the cable connection position selection process of the step 44 in
At the present stage, because the derivation of an EMI characteristic has already been completed with respect to the cable connection position candidate A, the cable connection position candidate B is selected next, according to the above-described method for determining a cable connection position.
Next, the board analysis means 5 of
Next, the board analysis means 5 of
Next, the EMI calculation means 6 of
Thus obtained characteristic becomes the one represented by a solid line in
Next, the EMI characteristic derivation means 2B of
Next, the EMI characteristic derivation means 2B of
Next, the board analysis means 5 of
Next, the board analysis means 5 of
Next, the EMI calculation means 6 of
Thus obtained characteristic becomes the one represented by a solid line in
Next, the EMI characteristic derivation means 2B of
Next, the EMI characteristic derivation means 2B of
Results of the comparison are shown in
Then, in the result output process of the step 51 in
At that time, simultaneously with the step 51 in
The above description is that of the series of processes according to the practical example of the fifth exemplary embodiment shown in
In the result output process of the step 51, for example, the two-dimensional CAD data shown in
As has been described above, if setting board design information and also setting an EMI permissive condition in the database, as in the present practical example, it is possible for even a person not having deep knowledge of electrical circuits and electromagnetic waves to perform PCB design, with the cable connection position candidate B corresponding to a cable connection position satisfying the EMI permissive condition being automatically set as the cable connector. Accordingly, it becomes possible for such a person to design a PCB structure and PCB specifications making common mode radiation generated from the cable become at a low level. While there are three cable connection position candidates 64 in the present practical example, analysis using a detailed board model needs to be performed with respect to only one pattern, and analysis using a simplified board model comes to have a considerably smaller analysis space than that of the detailed board model, and accordingly, it is possible to find an optimum cable connection position in a shorter time. Further, an EMI characteristic derived by means of the derivation method used by the present invention shows good agreement with a result of analysis using a detailed board model, as in the examples shown in
Although the present invention has been described above with reference to the exemplary embodiments and the practical example, the present invention is not limited to the above-described exemplary embodiments and practical example. To the configurations and details of the present invention, various changes which can be understood by those skilled in the art may be made within the scope of the present invention.
The present invention can be applied to a use where an EMI characteristic is to be derived at each design stage without spending a large cost, with respect to a PCB with a cable connected to it and with an LSI mounted on it.
It is also applicable to a use where an optimum cable connection position is to be automatically found such that it has a characteristic of EMI to occur satisfying a permissive condition, and a use where a design of a PCB is changes such as in the PCB structure.
A main usage of the system of the present invention is the one where a printed wiring board manufacturer use the system for the purpose of proposing a PCB board structure designed to make the EMI characteristic become at a low level, in relation to necessary operation of an LSI to be mounted on the PCB. By setting a general EMI standard as an EMI permissive condition with respect to a PCB structure including an LSI to be mounted on it, and then designing a board structure, a cable connection position and the like in a manner to satisfy the EMI permissive condition, by the use of the system of the present invention, it becomes possible to provide a board structure which can make a characteristic of generated EMI become at a low level even when the mounted LSI is in the necessary operation.
It is also possible for an LSI vender to use the system of the present invention for the purpose of providing an LSI configuration with a low EMI characteristic. At the vender side, the configuration of a PCB expected to be used by a user or that of a standard PCB is used as input information. By setting a general EMI standard as an EMI permissive condition, and then designing operation, a terminal condition and the like satisfying the EMI permissive condition by the use of the system of the present invention, it becomes possible to provide a user with an LSI capable of realizing a low EMI characteristic when mounted on a PCB.
Part or the whole of the above-described exemplary embodiments can also be described as, but is not limited to, the following supplementary notes.
(Supplementary Note 1)
A circuit board design system for designing a circuit board with a semiconductor component mounted on it and with a cable connected to it, the circuit board design system comprising:
an input means for inputting board design information about the board configuration of said circuit board;
an EMI characteristic derivation means for deriving a characteristic of EMI generated from said cable connected to said circuit board, on the basis of said board design information; and
a storage means for storing a cable length correction characteristic for deriving said EMI characteristic, wherein
said EMI characteristic derivation means has:
an analysis model creation means for creating, as an analysis model of said circuit board, a simplified analysis model with a simplified virtual cable arranged in it, on the basis of said board design information;
a board analysis means for calculating virtual cable current flowing in said virtual cable by performing electromagnetic field analysis of said simplified analysis model; and
an EMI calculation means for calculating actual cable current flowing in said cable by the use of said virtual cable current and said cable length correction characteristic, and then by the use of said actual cable current, calculating said characteristic of EMI generated from said cable.
(Supplementary Note 2)
The circuit board design system according to supplementary note 1, wherein
said storage means stores an EMI permissive condition corresponding to a permissive condition of said EMI characteristic, and
the circuit board design system further comprises an EMI characteristic determination means for comparing said EMI characteristic derived by said EMI characteristic derivation means with said EMI permissive condition.
(Supplementary Note 3)
The circuit board design system according to supplementary note 2, wherein:
said EMI characteristic derivation means
has a cable length correction characteristic derivation means for deriving said cable length correction characteristic on the basis of said virtual cable current;
said analysis model creation means
creates a detailed board model in which the actual cable is reproduced, as an analysis model of said circuit board;
said board analysis means
calculates actual cable current flowing in the actual cable of said detailed board model, by performing electromagnetic field analysis of said detailed board model; and
said cable length correction characteristic derivation means
calculates a cable length correction characteristic by the use of the actual cable current calculated by said detailed board model and of said virtual cable current, and stores the cable length correction characteristic calculated on the basis of said detailed board model into said storage means.
(Supplementary Note 4)
The circuit board design system according to supplementary note 3, wherein:
said board design information includes circuit board design information corresponding to configuration information on said circuit board, semiconductor integrated circuit design information corresponding to internal design information on a semiconductor integrated circuit arranged on said circuit board and cable structure design information corresponding to information on said cable;
said input means
inputs said pieces of information extracted from said board design information into said EMI derivation means; and
said EMI characteristic derivation means
stores, into said storage means, said cable length correction characteristic derived by said cable length correction characteristic derivation means on the basis of said pieces of information included in said board design information, and updates said board design information, according to said EMI characteristic and said EMI permissive condition.
(Supplementary Note 5)
The circuit board design system according to supplementary note 4, wherein:
said EMI derivation means
derives said EMI characteristic with respect to each of a plurality of cable connection position candidates for connecting said cable, which are set on said circuit board; and
said EMI characteristic determination means
determines whether or not said EMI characteristic with respect to each of a plurality of cable connection position candidates satisfies said EMI permissive condition.
(Supplementary Note 6)
The circuit board design system according to supplementary note 5, wherein a graph of comparing said EMI characteristic with respect to each of a plurality of cable connection position candidates with said EMI permissive condition is outputted.
(Supplementary Note 7)
The circuit board design system according to supplementary note 2,
further comprising a board configuration change means for changing said board configuration if said EMI characteristic determination means determines that said EMI permissive condition is not satisfied, wherein:
said storage means
stores a guideline on change of said board configuration;
said board configuration change means
changes said board design information on the basis of said guideline on change; and
said EMI characteristic derivation means
derives said EMI characteristic by the use of said changed board design information.
(Supplementary Note 8)
The circuit board design system according to supplementary note 7, wherein said EMI characteristics with respect to, respectively, said board design information before change and said board design information after change are outputted, along with graphs of comparing the EMI characteristics with said EMI permissive condition.
(Supplementary Note 9)
The circuit board design system according to supplementary note 7, wherein:
said board design information includes circuit board design information corresponding to configuration information on said circuit board, semiconductor integrated circuit design information corresponding to internal design information on a semiconductor integrated circuit arranged on said circuit board and cable structure design information corresponding to information on said cable; and
said EMI characteristic derivation means
stores, into said storage means, said cable length correction characteristic derived by said cable length correction characteristic derivation means on the basis of pieces of information extracted from said board design information, and updates said board design information, according to said EMI characteristic and said EMI permissive condition.
(Supplementary Note 10)
The circuit board design system according to supplementary note 9, wherein,
if said EMI characteristic does not satisfy said permissive condition:
said board configuration change means
changes said board configuration, on the basis of said guideline on change which suggests that either of said circuit board design information, said semiconductor integrated circuit design information and said cable structure design information, which are included in said board design information, is to be changed sequentially until said EMI characteristic satisfies said permissive condition; and
said EMI derivation means
derives said EMI characteristic on the basis of said board configuration after change, and
if said EMI characteristic satisfies said permissive condition,
said board design information with respect to which said EMI characteristic satisfying said permissive condition is obtained is outputted.
(Supplementary Note 11)
The circuit board design system according to any one of supplementary notes 1 to 10, wherein the length of said virtual cable is set at a value equal to or smaller than ¼ of a wavelength corresponding to the maximum frequency in a frequency range where said EMI characteristic is to be derived.
(Supplementary Note 12)
A circuit board design method for designing a circuit board with a semiconductor component mounted on it and with a cable connected to it, the circuit board design method comprising:
inputting board design information on said circuit board;
creating, as an analysis model of said circuit board, a simplified analysis model with a simplified virtual cable arranged in it, on the basis of said board design information;
calculating virtual cable current flowing in said virtual cable by performing electromagnetic field analysis of said simplified analysis model;
calculating actual cable current flowing in said cable by the use of a cable length correction characteristic for deriving an EMI characteristic and said virtual cable current; and
calculating said characteristic of EMI generated from said cable by the use of said actual cable current.
(Supplementary Note 13)
The circuit board design method according to supplementary note 12, comprising:
setting an EMI permissive condition corresponding to a permissive condition of said EMI characteristic; and
comparing said EMI characteristic with said EMI permissive condition.
(Supplementary Note 14)
The circuit board design method according to supplementary note 13, comprising:
creating a detailed board model in which the actual cable is reproduced, as an analysis model of said circuit board, and calculating actual cable current flowing in the actual cable of said detailed board model, by performing electromagnetic field analysis of said detailed board model;
calculating a cable length correction characteristic by the use of the actual cable current calculated by said detailed board model and of said virtual cable current; and
using said cable length correction characteristic calculated on the basis of said detailed board model in said EMI characteristic derivation.
(Supplementary Note 15)
The circuit board design method according to supplementary note 14, comprising:
recording said cable length correction characteristic derived by the use of said board design information including circuit board design information corresponding to configuration information on said circuit board, semiconductor integrated circuit design information corresponding to internal design information on a semiconductor integrated circuit arranged on said circuit board and cable structure design information corresponding to information on said cable;
updating said board design information, according to said EMI characteristic and said EMI permissive condition.
(Supplementary Note 16)
The circuit board design method according to supplementary note 15, comprising:
setting a plurality of cable connection position candidates for connecting said cable, on said circuit board;
deriving said EMI characteristic with respect to each of said plurality of cable connection position candidates; and
determining whether or not said EMI characteristic with respect to each of a plurality of cable connection position candidates satisfies said EMI permissive condition.
(Supplementary Note 17)
The circuit board design method according to supplementary note 16, wherein,
if it is determined that said EMI permissive condition is not satisfied,
said board design information is changed on the basis of a guideline on change of said board configuration, and
said EMI characteristic is derived using said changed board design information.
(Supplementary Note 18)
The circuit board design method according to supplementary note 17, comprising:
recording said cable length correction characteristic derived by the use of said board design information including circuit board design information corresponding to configuration information on said circuit board, semiconductor integrated circuit design information corresponding to internal design information on a semiconductor integrated circuit arranged on said circuit board, and cable structure design information corresponding to information on said cable; and
updating said board design information, according to said EMI characteristic and said EMI permissive condition.
(Supplementary Note 19)
A circuit board design program, in a circuit board design system for designing a circuit board with a semiconductor component mounted on and a cable connected to it, the circuit board design program causing a computer to execute:
a process of inputting board design information on said circuit board;
a process of creating, as an analysis model of said circuit board, a simplified analysis model with a simplified virtual cable arranged in it, on the basis of said board design information;
a process of calculating virtual cable current flowing in said virtual cable by performing electromagnetic field analysis of said simplified analysis model;
a process of calculating actual cable current flowing in said cable by the use of a cable length correction characteristic for deriving an EMI characteristic and said virtual cable current; and
a process of calculating said characteristic of EMI generated from said cable by the use of said actual cable current.
(Supplementary Note 20)
The circuit board design program according to supplementary note 19, causing the computer to execute:
a process of setting an EMI permissive condition corresponding to a permissive condition of said EMI characteristic; and
a process of comparing said EMI characteristic with said EMI permissive condition.
(Supplementary Note 21)
The circuit board design program according to supplementary note 20, causing the computer to execute:
a process of creating a detailed board model in which the actual cable is reproduced, as an analysis model of said circuit board, and calculating actual cable current flowing in the actual cable of said detailed board model, by performing electromagnetic field analysis of said detailed board model;
a process of calculating a cable length correction characteristic by the use of the actual cable current calculated by said detailed board model and of said virtual cable current; and
a process of calculating said EMI characteristic by the use of said cable length correction characteristic calculated on the basis of said detailed board model.
(Supplementary Note 22)
The circuit board design program according to supplementary note 21, causing the computer to execute:
a process of recording said cable length correction characteristic derived by the use of said board design information including circuit board design information corresponding to configuration information on said circuit board, semiconductor integrated circuit design information corresponding to internal design information on a semiconductor integrated circuit arranged on said circuit board, and cable structure design information corresponding to information on said cable; and
a process of updating said board design information, according to said EMI characteristic and said EMI permissive condition.
(Supplementary Note 23)
The circuit board design program according to supplementary note 22, causing the computer to execute:
a process of setting a plurality of cable connection position candidates for connecting said cable, on said circuit board;
a process of deriving said EMI characteristic with respect to each of said plurality of cable connection position candidates; and
a process of determining whether or not said EMI characteristic with respect to each of a plurality of cable connection position candidates satisfies said EMI permissive condition.
(Supplementary Note 24)
The circuit board design program according to supplementary note 23, causing the computer to execute,
if it is determined that said EMI permissive condition is not satisfied:
a process of changing said board design information on the basis of a guideline on change of said board configuration; and
a process of deriving said EMI characteristic by the use of said changed board design information.
(Supplementary Note 25)
The circuit board design program according to supplementary note 24, causing the computer to execute:
a process of recording said cable length correction characteristic derived by the use of said board design information including circuit board design information corresponding to configuration information on said circuit board, semiconductor integrated circuit design information corresponding to internal design information on a semiconductor integrated circuit arranged on said circuit board, and cable structure design information corresponding to information on said cable; and
a process of updating said board design information, according to said EMI characteristic and said EMI permissive condition.
The present invention has been described above with reference to the exemplary embodiments and the practical example, but the present invention is not limited to the above-described exemplary embodiments and practical example. To the configurations and details of the present invention, various changes which are understandable to those skilled in the art may be made within the scope of the present invention.
This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2012-255557, filed on Nov. 21, 2012, the disclosure of which is incorporated herein in its entirety by reference.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2012-255557 | Nov 2012 | JP | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2013/006761 | 11/18/2013 | WO | 00 |
