JP2000137742A - Lsi power system model for emi simulation, and emi simulation - Google Patents

Abstract

PROBLEM TO BE SOLVED: To accurately and easily perform EMI simulation from a printed board power system. SOLUTION: This model 30 has an LSI modeled as one variable resistance 20 or transistor according to the LSI source current waveform. Its resistance value varies with the voltage at a power supply terminal 35 and time and behaves similarly to the power supply system of the object LSI. Consequently, an electromagnetic field produced by the power supply system can accurately be simulated with a small calculation quantity. The model is generated from the source current waveform, so an LSI maker can provide a model for a user without leaking secret information such as circuit information on the inside of the LSI to others.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an EMI simulator, and more particularly to an EMI simulator using an LSI model in which the impedance of a power supply system changes with time.

[0002]

2. Description of the Related Art It is effective and economical to take measures at the design stage to suppress electromagnetic radiation noise generated from electronic equipment. Therefore, many designers take an EMI simulator into the design and take measures. However, the reality is that the simulation result does not always match the actually measured value. One of the causes is that many simulators do not analyze the power supply system.

FIG. 16 is a system configuration diagram of a conventional EMI simulator. There are several simulation methods. In this system, a current is obtained by circuit simulation, and an electromagnetic field is calculated from the current. The configuration of the conventional EMI simulator is mainly LS
I / O section model generation section 44, printed circuit board wiring model generation section 17, LSI package model generation section 19, chip component model generation section 21, net list generation section 22,
It comprises a circuit simulation execution section 26, an electromagnetic field simulation execution section 23, and display sections 24 and 25. First, the net list generation unit 22 determines whether each of the model generation units 44, 17, 1
The respective models are read from 9, 21 to create one circuit system model (netlist). Using this netlist, the circuit simulation execution unit 26 obtains the current and voltage of an element (in many cases, a conductor of a printed circuit board) serving as an antenna that emits an electromagnetic field, and the display unit 25 displays the current and voltage. Further, the electromagnetic field simulation unit 23
Calculates the electromagnetic field radiated from the printed circuit board or the like from the current and voltage obtained by the circuit simulation executing unit 26, and displays the spectrum of the electromagnetic field on the display unit 24. ("EMI
"Simulation Technology", "Electric and Electronic Equipment Workshop-Communication and EMC-", 9th document, October 1998
Monthly publication p143, p77-79, see Figure 2-1)) LS currently used in such EMI simulators
As a representative of the I model, there is an IBIS model. IBI
S is an abbreviation of I / O Buffer Information Specification, and is a model of an input buffer and an output buffer as their names indicate. In an EMI simulator based on SPICE (circuit simulator), a current is obtained by incorporating such a circuit element model, and a radiation electromagnetic field is calculated from the current. SPICE is Simulation P
rogram with Integrated cirucuitEmphasis.

As can be seen from the above, an existing EMI simulation model of an LSI is considered mainly for analyzing a signal system of the LSI, and no analysis method for other terminals such as a power supply terminal and a GND terminal is considered.
("Change in board design, pre-verification is required in the advent of the 100 MHz era," Nikkei Electronics, 1998, 4
-6 Published April 1998 p143, p111,
However, actually, not only the I / O buffer, but also all the internal circuits not directly related to the signal terminals are connected to the power supply current of the LSI, and the LSI contains more high-frequency components. Radiated electromagnetic fields due to power supply current cannot be ignored.

Therefore, in order to analyze EMI of an electronic device, it is essential to analyze a power supply current of a printed circuit board and analyze a radiation electromagnetic field generated by the power supply current. The problem arises here. When analyzing EMI on a printed circuit board, a model of an LSI mounted on the printed circuit board is required in addition to a transmission line model of the printed circuit board wiring. As a model format of this LSI, there are a transistor description format and an operation level description format. The transistor description format accurately describes the circuit configuration inside the LSI using a transistor model and a model of resistance and capacitance of wiring, and is generally used for LSI design. The operation level description format is a simplified version of the transistor description format.
An operation level description format is used for noise verification of a printed circuit board. (The IBIS model described above is also in this behavioral level description format.) Consider a case in which a radiated electromagnetic field from a power supply is analyzed using these two models.

First, when a power supply current is obtained in a transistor description format, it is necessary to analyze all circuits inside the LSI, but the circuit scale inside the LSI is enormous. FIG. 8 is a schematic diagram of an equivalent circuit for analysis in a transistor description format. For example, about 5000 transistors are internally formed in a mask ROM having a relatively small circuit scale.
In the case of an MPU having a large number of circuits and a large circuit scale, the number of transistors is one million or more.

In the conventional analysis of only the signal terminals, an LSI
Can be omitted only for the I / O buffer, but since all the circuits are connected to the power supply terminal, the circuit cannot be omitted.

Therefore, the calculation amount of the EMI simulator is enormous as compared with the signal system, and it is difficult to perform the analysis, and in some cases, it becomes impossible.

[0009] Further, the user sets the LSI model to LS.
I need to receive it from the I maker, but the transistor description level model is
It contains a lot of information that is confidential to LSI manufacturers, such as the circuit configuration inside the SI. Therefore, LSI manufacturers cannot provide transistor description models to users of other companies.

In the case where the analysis is performed using the behavioral level description description format, the following model is currently proposed.

A conventional behavioral level description model of an LSI power supply system is composed of a current source and an impedance connected in parallel to the current source as shown in FIG. The power supply current waveform 41 of the LSI is reproduced from the current source 39.

However, this has a problem.

Originally, the internal impedance of an LSI changes depending on the input state of a signal and the voltage of a power supply terminal. This change in impedance causes a current waveform to flow through the complicated power supply terminal.

However, in the case of this model, the internal impedance is fixed, and the current waveform is reproduced by a change in the current value of the internal current source.

Therefore, even if the voltage of the power supply terminal changes, for example, the internal resistance value does not change, so that an accurate current waveform cannot be reproduced.

FIG. 10 shows an analysis result by a conventional behavioral level description format model. (A) is a power supply current based on a transistor description model, and (b) is an operation level description model. Here, an LSI model having a relatively small circuit scale is used, and analysis using a transistor description model is compared as far as possible.

It can be seen that the power supply current according to the transistor description model greatly changes due to the change in the power supply voltage (Vdd) 37, whereas the power supply current peak hardly changes in the conventional operation level description model. This indicates that the power supply current cannot be accurately analyzed by the conventional behavioral level description model. ("Models of Integrat
ed Circuits for EMI Behavioral Simulation ”, IEC T
C93 New Work Item Proposal, 1997.5.15 1995
Published in May, p4, FIG. (See (3))

[0018]

The first problem is that it is impossible to analyze the power supply system of the LSI with the conventional transistor description model.

The reason is that the circuit scale inside the LSI is enormous, and it is difficult to simulate by omitting circuits as in the analysis of signal terminals.

The second problem is that it is impossible for an LSI maker to present a model to a user with a conventional transistor description model.

The reason is that the transistor description model contains a lot of confidential information such as the transistor structure and the circuit configuration inside the LSI.

A third problem is that an accurate current waveform cannot be reproduced by the conventional operation level description model.

The reason is that the internal resistance value is constant without depending on time and power supply voltage.

[0024]

SUMMARY OF THE INVENTION An object of the present invention is to provide an EMI simulator and a simulation model for accurately and easily performing an EMI simulation from a printed circuit board power supply system, which has been difficult in the past.

[0025]

The EMI simulator of the present invention simulates a radiated electromagnetic field generated on a printed circuit board using an LSI device model expressed in a behavior level description format.

This behavioral level description model is a model in which the impedance of the LSI power supply system changes with time and power supply voltage. The EMI simulator uses this model to find the power supply current flowing on the printed circuit board wiring. As a circuit configuration of this model, the power supply system is configured by one MOS transistor, and the power supply current is controlled by changing the gate voltage of this transistor. This model is created from the waveform of the power supply current of the LSI.

[0027]

The power supply system of the LSI is modeled by a variable resistor or a single MOS transistor, so that the calculation load is reduced as compared with the conventional transistor description model, and the power supply current can be easily analyzed. .

This resistance changes depending on the power supply voltage and time, and the actual LS is smaller than that of the conventional operation level description model.
Since the behavior is close to the operation of I, the power supply current of the LSI can be reproduced more accurately.

[0029]

Next, a first embodiment of the present invention will be described in detail with reference to the drawings. FIG. 1 is a system configuration diagram of the EMI simulator of the present invention. As shown in FIG. 1, the EMI simulator of the embodiment
The LSI power supply current time waveform (power supply voltage dependent) capture unit 12 that reads the power supply current waveform of the LSI used to create the I power supply system model, and the LSI power supply current time waveform (power supply voltage dependent) capture unit 12 that reads the power supply current waveform Transistor DC characteristic creation unit 11 for creating transistor DC characteristics from current waveform
And LSI power supply current time waveform (power supply voltage dependent) capture unit 1
2, a gate voltage waveform generator 14 for generating a gate voltage waveform from the read current waveform, a transistor DC characteristic generated by the transistor DC characteristic generator 11 and a gate voltage waveform generated by the gate voltage waveform generator 14 are combined to form an LSI power supply. An LSI power supply system model creation unit 13 for creating a system model, a printed circuit board data acquisition unit 16 for acquiring printed circuit board data (layer thickness, dielectric constant, and wiring coordinates); A printed circuit board wiring model generation unit 17 modeled as
An LSI package data capturing unit 18 for capturing data (thickness, permittivity, coordinates) of the SI package, an LSI package model generating unit 19 for modeling the LSI package as a lumped circuit or a transmission line, and a chip component (capacitor, coil) And the like, a chip component data acquisition unit 20 for reading data (frequency characteristics of impedance, etc.), a chip component model generation unit 21 for modeling a capacitor or a coil as a circuit model, and a model generation unit 1
The respective models are read from 3, 17, 19, and 21, and a netlist generation unit 22 that generates one circuit system model (netlist), and functions as an antenna in the netlist generated by the netlist generation unit 22 A circuit simulation execution unit 26 for analyzing the voltage and current of a component (mainly a printed circuit board wiring); an electromagnetic field simulation unit 23 for obtaining a radiation electromagnetic field from the voltage or current obtained by the circuit simulation execution unit 26; A radiated electromagnetic field display unit 24 for displaying the radiated electromagnetic field determined by the unit 23, and a circuit simulation execution unit 26
And a display unit 25 for displaying the obtained voltage and current.
In some cases, each of the model generators 13, 17, 19,
By linking the model library 21 with the model library reading unit 27, model data can be stored and read as a library.

The net list generation unit 22 reads each model from each of the model generation units 13, 17, 19, and 21 and generates one circuit system model (net list).
Using this netlist, the circuit simulation execution unit 26 obtains current and voltage, and the display unit displays the current and voltage. Further, the electromagnetic field simulation unit 23 calculates the electromagnetic field radiated from the printed circuit board from the current and voltage obtained by the circuit simulation execution unit 26, and displays the spectrum of the electromagnetic field on the display unit 24. The operation level description model of the EMI simulation LSI power supply system created by the LSI power supply system model creation unit 15 in FIG.
FIG. 2 shows an equivalent circuit of an LSI power supply system model).
Variable resistor 29 and voltage source 28 for controlling the resistance value
It is composed of

Further, as shown in FIG. 3, if the MOS transistor 31 is used as a variable resistor, an LSI power supply system model can be easily created. Next, the operation of the first embodiment will be described. First, a power supply current waveform of an LSI to be modeled is obtained. This waveform is obtained with only the ideal voltage source and the LSI connected. It is preferable to obtain the current waveform while the load is not connected to the power supply system as much as possible. At this time, the power supply voltage is changed within a range where the LSI operates normally, and a current waveform for each power supply voltage is obtained. FIG. 4 shows an example of the power supply current waveform. In the example shown in FIG. 4, the power supply voltage (Vdd) is 4.5.
Three current waveforms of V, 5.0 V and 5.5 V are obtained. The LSI power supply current time waveform acquisition unit 12 reads this current waveform and displays a time-dependent change of the power supply current to the user. The user specifies an arbitrary number of points in the waveform using a pointing device such as a mouse. Although the designated point may be one point, it is desirable to designate as many current values as possible. This is because the characteristics of the transistor can be accurately reproduced. In the example shown in FIG. 4, three points A, B, and C are extracted. The LSI power supply current time waveform acquisition unit 12 stores the current values of the designated points A, B, and C, and transfers the current values to the transistor DC characteristic generation unit 11. In addition, the power supply current acquisition unit 12 transfers one representative current waveform to the gate voltage waveform generation unit 14. The transistor DC characteristic extraction unit 11 determines the DC characteristic of the transistor to be a model from the current value at the designated point. The horizontal axis is the gate-source voltage of the transistor, and the vertical axis is the drain current of the transistor. FIG. 5 is a graph plotting the current value at the designated point determined by the power supply current time waveform acquisition unit 12 on the vertical axis, and plotting the product of the current value at the designated point and an arbitrary coefficient n on the horizontal axis. The coefficient n may be any value. The transistor DC characteristic generation unit 11 automatically generates a transistor model having a DC characteristic that matches this graph. The model of this transistor is shown in FIG.
Used as the transistor 31.

On the other hand, the gate voltage waveform generating section 14 outputs the current waveform (hereinafter, Id) transferred from the power supply current waveform capturing section 12.
d0) is determined from the following equation.

Vlsi = Idd0 × n Equation (1) The voltage Vlsi is used as the output waveform of the voltage source 28 in FIG. FIG. 5 is an example of the output waveform of the voltage source.

With the above method, the LSI power supply system model 30 of FIG. 3 is completed. The netlist generation unit 22 configures the power supply system model, the printed circuit board wiring model, the chip component model, the LSI package model, and the like as one circuit system model (netlist). FIG. 7 is a schematic diagram of this circuit configuration. The subsequent operation is the same as that of the conventional EMI simulator.
Obtains a current or a voltage flowing through an element acting as an antenna (in most cases, a printed circuit board wiring) from the netlist, and the electromagnetic field simulation execution unit 23 calculates a radiation electromagnetic field from the current and the voltage. The calculated radiated electromagnetic field, voltage and current are displayed on the display units 24 and 25 to the user. Next, a second embodiment of the present invention will be described. In the first embodiment described above, LS
Although all the power supply systems of I are summarized as one model, the inside of an actual LSI is a set of several small circuit blocks. Therefore, if the power supply system model of the present invention is created for each of the small circuit blocks and simulated as one LSI power supply system, it becomes easy to create the LSI power supply model and the netlist.

FIG. 12 shows the simulation model as an I / O
It is an example of an equivalent circuit divided into an internal circuit 30 having no direct relation to a signal from a unit 46.

The load connected to the I / O section 46 of the LSI differs depending on the circuit configuration on the printed circuit board. If the load capacitance of the output terminal differs, the power supply current of the I / O unit 46 also changes. Therefore, if the circuit configuration shown in FIG.
By reproducing the change of the power supply current by the load connected to the unit 46, the simulation can be easily executed without changing the model even if the load of the signal terminal 47 changes.

FIG. 12 is a system configuration diagram for creating the equivalent circuit model of FIG. In addition to the system configuration diagram of FIG. 1, a part 4 for taking in data of the I / O part of the LSI
3 and a part 44 for creating a model of the I / O part are added. These blocks can easily constitute a system by using the functions of the existing EMI simulator.
Further, if the circuit scale is relatively small, the LSI
It is also possible to create a power supply system model for each circuit block constituting.

FIG. 14 shows a simulation equivalent circuit diagram. Since many LSIs are configured by combining basic circuit units called cells, circuits are prepared. At the stage of designing cells, a model 49 of the present invention is prepared for each cell, and FIG.
If the LSI model 48 is an aggregate of the models 49 as in 3, the LSI model 48 can be easily created.

In particular, if a power supply system model 49 is created for each cell used in a circuit having a periodic operation such as a clock system, and the configuration shown in FIG. Can be created.

Although a plurality of power supply system models are used in FIG. 13, it is also possible to combine a plurality of power supply system models into one or a small number of models as shown in FIG. This finds the power supply current of the circuit model using the model 49, and calculates L from the power supply current in the manner shown in FIG.
A model 30 of the entire SI can be created.

FIG. 15 shows a system configuration for reducing a large number of power supply system models as shown in FIG.

Here, the circuit block power supply system model 49
Then, an LSI power supply system model 30 is created by adding current waveforms flowing through the power supply terminal 35 according to the above. The power supply current of the circuit block power supply system model 49 is captured by the current waveform capturing unit 50, the current waveform is superimposed by the current waveform adding unit 52, the current waveform of the entire LSI is obtained, and the data is transferred to the LSI model generation unit. For example, a model 30 of the entire LSI can be created. At this time, each circuit block is provided with delay information, and if the delay information of the circuit block 49 is read by the circuit block delay information capturing unit, the analysis can be performed more accurately.

[0043]

The first effect is that the electromagnetic field radiated from the power supply system can be easily analyzed. The reason is that the operation model used in the EMI simulator of the present invention simplifies the inside of the LSI. Second
Is that the current flowing through the power supply system of the printed circuit board can be reproduced more accurately than before. The reason is,
This is because the inside of the LSI is represented by a model in which the impedance changes with time and power supply voltage. A third effect is that information in the LSI internal circuit does not leak to the user. For this reason, it is easy to open to the public. The reason is that the model used in the present invention is generated from the waveform of the power supply current and does not use the circuit information inside the LSI.

[0044]

[Brief description of the drawings]

FIG. 1 is a system configuration diagram of an EMI simulator of the present invention.

FIG. 2 is an equivalent circuit of an operation level description model of an LSI power supply system for EMI simulation of the present invention.

FIG. 3 is an equivalent circuit of an operation level description model of an LSI power supply system for EMI simulation of the present invention.

FIG. 4 shows an example of a current waveform used when obtaining an LSI power supply system model used in the EMI simulator of the present invention.

FIG. 5 is an example of a waveform of a voltage source Vlsi used in an LSI power supply system model of the present invention.

FIG. 6 shows M used in an LSI power supply system model of the present invention.
Example of DC characteristics of OS transistor

FIG. 7 shows an example of a simulation equivalent circuit using the LSI power supply system model of the present invention.

FIG. 8 shows an example of a simulation equivalent circuit using a conventional transistor description model.

FIG. 9 shows an operation level description format model of a conventional LSI power supply system.

FIG. 10 shows a calculation accuracy of a power supply current using a conventional operation level description model of an LSI power supply system.

FIG. 11 shows a second embodiment of the present invention (system configuration diagram).

FIG. 12 shows a second embodiment (simulation equivalent circuit) of the present invention.

FIG. 13 shows a second embodiment of the present invention (simulation equivalent circuit).

FIG. 14 shows a second embodiment (equivalent circuit) of the present invention.

FIG. 15 shows a second embodiment of the present invention (system configuration diagram).

FIG. 16 is a system configuration diagram of a conventional EMI simulator.

[Explanation of symbols]

11: MOS transistor DC characteristic generation unit 12: LSI power supply current time waveform (power supply voltage dependent) acquisition unit 13: LSI power supply system model generation unit 14: Gate voltage waveform generation unit 15: LSI power supply system model generation and generation unit 16: Print Board data acquisition unit 17: Printed circuit board wiring model creation unit 18: LSI package data acquisition unit 19: LSI package model creation unit 20: Chip component data acquisition unit 21: Chip component model creation unit 22: Net list configuration unit 23 : Electromagnetic field simulation execution unit 24: Radiated electromagnetic field display unit 25: Voltage and current display unit 26: Circuit simulation execution unit 27: Model library import unit 28: Voltage source (Vlsi) 29: Variable resistor 30: LSI of the present invention Power supply system model 31: MOS transistor model 32: Constant voltage source 33: Transmission Path 34: Capacitor model 35: Power supply terminal 36: GND terminal 37: Constant voltage source 38: Transmission line model 39: Current source 40: LSI internal impedance 41: Current waveform of current source 42: Description of operation level of conventional LSI power supply system Model 43: LSI I / O unit data acquisition unit 44: LSI I / O unit model creation unit 45: I / O buffer model 46: LSI input / output unit 47: LSI signal terminal 48: LSI power supply system model 49: Present invention Circuit block power supply system model 50: Circuit block power supply current time waveform (power supply voltage dependent)
Acquisition unit 51: Circuit block model generation unit 52: Current waveform addition unit 53: Circuit block delay information acquisition unit 54: LSI power supply system model generation unit

Claims (10)

[Claims] 1. An LSI power supply model for EMI simulation, wherein the resistance value of the LSI power supply changes according to time and power supply voltage. 2. An LSI power supply for EMI simulation, wherein an LSI power supply system is modeled by one or more transistors and a constant voltage source, and the impedance of the LSI power supply system changes according to time and power supply voltage. System model. 3. The LSI power supply model for EMI simulation according to claim 2, wherein a voltage waveform similar to a power supply current waveform is applied to the gate electrode of said transistor as a signal. 4. An LSI power supply system model for EMI simulation, wherein said transistor is a MOS transistor having a characteristic that a gate voltage is proportional to a drain current. 5. The LSI power supply model for EMI simulation according to claim 1, further comprising an LSI input / output model. 6. The EMI simulation LSI power supply system model according to claim 1, wherein an EMI simulation LSI power supply system model is provided for each of several circuit blocks or functional blocks. 7. The EMI simulation LSI power supply system model according to claim 1, wherein the LSI power supply model is created from a current waveform of a circuit having periodicity. 8. An EM simulation LSI power supply system model for one LSI is created from the operating states of a plurality of EMI simulation LSI power supply system models for each circuit block or function block.
LSI simulation system for I simulation. 9. An EMI simulator for simulating a radiated electromagnetic field from an electronic device, wherein the simulated radiated electromagnetic field creates an LSI power supply system model for EMI simulation according to claim 1. And
EMI characterized by using this to simulate
Simulator. 10. The EMI simulation L according to claim 1, which is stored as a library.
The EMI simulator according to claim 9, wherein data of the SI power supply system model can be stored and read.