JPH0282346A - Logic simulation system for switching element - Google Patents

Abstract

PURPOSE:To simulate a logic in consideration of the capacity by defining a driving power and using this definition to evaluate the driving power and a net value and obtaining a logical level of each connection point in accordance with the driving power. CONSTITUTION:When one switching element is changed, the driving power to the connection point to which this switching element is connected is divided into two by direction, and the net value (voltage level) of the connection point is obtained in a net evaluating means 1 by the driving power in each direction. A driving power evaluating means 2 obtaines the driving power of the switching element for the purpose of obtaining the net value of the connection point to which the switching element whose turning-on/off state is changed is connected. The net value is obtained again in accordance with this driving power by a net evaluating means 1. A control means 3 controls this repetition, and this operation is repeated until the net value is not changed. Thus, a logic circuit consisting of switching elements is simulated.

Description

[Detailed Description of the Invention] [Summary] Regarding a switching element logic simulation method that simulates the logic of a bidirectional element such as an MO3 circuit, the driving force is determined by the on/off state of a bidirectional switching element such as an MO3 circuit. The purpose of this study is to calculate the logic level of each connection point from the driving force and perform a logic simulation that also takes capacitance into account. a net evaluation means for evaluating a net value of a connection point; and a drive for determining the driving force of a switching element different from the switching element whose gate is connected to the connection point when the net value obtained by the net evaluation means changes. A force evaluation means, and a control means for operating the net evaluation means and the driving force evaluation means again based on the driving force obtained by the driving force evaluation means to obtain a final net value and driving force. .

[Industrial application field]

The present invention relates to a logic circuit simulation method, and more particularly to a switching element logic simulation method for simulating the logic of a bidirectional element such as an MO3 circuit.

[Conventional technology]

With the development of electronic technology, various control circuits and the like are controlled digitally. Furthermore, so-called large-scale integrated circuits (VLSI), in which digital circuits are integrated into one LSI, have been realized and are widely used for controlling purposes.

VLSI must be verified at its development stage to ensure that it performs the intended operations. Because, VLS
This is because if there is a design error or the like in one gate constituting I, there is a problem that the created VLSI becomes unusable.

For this reason, we performed logic simulations of the designed VLSI. For example, what kind of signals are applied to multiple input terminals, which gates change how in response to the applied multiple signals, and are output to other gates, etc., and the elements that make up the VLS The logic value was determined and it was verified whether the desired logic was output from that logic value.

[Problem to be solved by the invention]

With the development of semiconductor technology, for example, in addition to VLSIs made up of bipolar transistors, VLSIs using bidirectional elements have been developed and used.

In conventional logic circuits using, for example, bipolar transistors, the input and output are completely separated, so in conventional simulations, they can be separated into input and output. However, in the case of MO3 circuit, MOS
By turning on the gate, current may flow from the source to the drain and from the drain to the source.
The problem was that it was difficult to separate input and output. For this reason, conventionally, in logic simulations using MO3 circuits, verification was not performed at the overall level, but rather a large number of partial verifications were performed. For this reason, there was also the problem that many verifications were missed.

Furthermore, a method is also used in which the MO3 circuit is converted to the gate level so that it can be verified by conventional simulation. However, since this method simply converts the MO3 circuit to the gate level, there is a problem in that circuit design is restricted when using this method.

On the other hand, in the MO3 circuit, when the gate is turned off, the signal value may be determined by the capacitance of the circuit itself. However, the conventional method also has the problem of not performing simulations that take any capacitance into account.

The present invention calculates the driving force based on the on/off state of a bidirectional switching element such as an MO3 circuit, calculates the logic level of each connection point from the driving force, and performs a logic simulation that also takes capacitance into consideration. With the goal.

[Means to solve the problem]

FIG. 1 is a block diagram of the principle of the present invention.

The net evaluation means 1 divides the driving force to the connection point to which the switching element is connected into two according to the direction, and calculates the net of the connection point (I).
Evaluate lj. For example, the groups are further divided into levels and evaluated, depending on various levels, such as whether the element driving the connection point is a direct power supply, a drive via a resistor, or a capacitive drive.

The driving force evaluation means 2 determines the driving force of the switching element whose gate is connected to the net when the net value obtained by the net evaluation means 1 changes. When the switching element changes from off to on or from on to off, the driving force that drives each connection point changes, so
The driving force evaluation means 2 determines the driving force to each connection point based on the on/off changes of this switching element.

The control means 3 repeatedly operates the net evaluation means 1 and the driving force evaluation means 2 again from the driving force obtained by the driving force evaluation means 2 to obtain a final net value and driving force. Even if one net value changes, the switching element whose gate is connected to the connection point will change in response to the net value, so the driving force and net seek.

[For production]

For example, when one switching element changes, the driving force to the connection point to which the switching element is connected is divided into two depending on the direction, and the net value of the connection point, the so-called voltage level, is calculated from the driving force in each direction using the net evaluation means 1. Find it by

Another gate is connected to the connection point, and changes in the net value change the state of the switching element connected to that gate, the so-called on/off state. This on
In order to obtain the net value of the connection point to which the switching element whose ON/OFF state has changed due to the change in OFF state is connected, the driving force evaluation means 2 obtains the driving force of the switching element.

Using the driving force of the switching element determined by the driving force evaluation means 2, the net value is determined again by the net evaluation means 1.

The control means 3 controls this repetition until the net value finally stops changing. By repeating this process, it is possible to simulate a logic circuit constituted by switching elements.

〔Example〕

Embodiments of the present invention will be described in detail below using the drawings.

FIG. 2 is a processing flowchart in the logic simulation of the present invention.

When a change occurs in, for example, an input (an input terminal of VLSI) of a logic circuit (STI)=processing is started. In the present invention, as shown in the symbol explanatory diagram of FIG.
Let BWlo and BWII be the driving forces to each connection point to be driven by the switching element SWI made of a transistor.

The driving forces BWIO and BWII each have directionality, and the driving force applied from one connection point to the other connection point is
ll, the driving force applied from the other connection point to one connection point is BWIO. As will be described later, this driving force changes depending on the evaluation value at which each connection point is driven.

In the embodiment of the present invention, this driving force is defined by the following 19 types.

Driving force DHX to H level by DH direct power supply Driving force DL to which driving force to H level by direct power supply may be transmitted Driving force to L level DLX by direct ground Driving force to L level by direct ground is transmitted Possible driving force RH Driving force RH to H level by the power supply via a resistor Driving force RL to H level due to the power supply via a resistor To L level by ground via a resistor Driving force RLX Driving force to L level due to ground via resistor may be transmitted Driving force CH% Driving force to H level due to charge CHX Driving force to H level due to static charges may be transmitted Driving force CL Driving force CLX to L level due to static charge
Driving force DCX in which the driving forces DCDH and DL collide, where the driving force to L level due to static charge may be transmitted. Driving force in which the driving forces RCRH and RL collide, in which the collision of the driving forces of DH and DL may be transmitted. Force RCX Driving force where collision between the driving forces of RH and RL may be transmitted Driving force where CCCH and CL collide CCX Driving force φ where collision between the driving forces of CH and CL may be transmitted No driving force Here A driving force whose symbol ends with an X is used when there is only a possibility that the driving force is present because it is unknown whether the driving force is transmitted or not, that is, whether the switching element is in an on state or an off state.

Returning to FIG. 2, the explanation will be continued. Driving force changes (ST
In case 1), the net value driven by the driving force is then evaluated (ST2). As mentioned above, driving force is defined. For example, when an external switch called DL changes the driving force from a direct ground to an L level to an H level from a direct power source, such as DH, the changed drive A net value for the force is determined in process ST2. The net value is the state value of the connection point of the switching element described above. In the embodiment of the present invention, the net state value is the following 611 class.

H high level.

L Low level.

Z High impedance.

X Undefined (I don't know if it's high level or low level).

ZH high impedance or high level, ZL
High impedance or low level, net state There are the six states described above, and the determination of this state value is determined by the old state value of the net and all driving forces to that net. That is, when evaluating in process ST2, all driving forces are first calculated. Then, the change in the net state value due to the driving force is evaluated. In order to find out what happens to all the driving forces, in the embodiment of the present invention, four levels of driving forces and two groups are evaluated.

FIG. 5 is an explanatory chart of the levels and groupings mentioned above. In the group value, level 1 is DHDL DC, level 2 is RHRL RC, level 3 is CHCL C
C, level 4 is φ, and in group 2, level 1 is DHX DLX DCX, level 2 is RHX R
LX RCX, level 3 CHX CLX CC
It is classified as X.

The level represents the driving force, with level 1 being the strongest, level 2, level 3, and level 4 having the strength in that order.

Process 5T of evaluating the net value driven by the aforementioned driving force
12, the 19 driving forces defined first are grouped into group I.
, Group 2 and Level 1 to Level 4 types. Then, group 1 and group 2
Allocating all the driving forces for each of them, the strongest level of driving force is determined. When the strongest driving force of group 1 is stronger than the strongest driving force of group 2, the state value is determined according to the level within each group 1 as follows.

When the level of the strongest driving force in group 1 is level 1, when all the driving forces at level 1 are DH, the state of the new circuit is H.
, When the driving force of level 1 is all DK, the state value of the new circuit is L. Otherwise, the state of the new circuit is X. - When the driving force of level 1 is all RH at level 20, the state value of the new circuit is H. When all driving forces at level 2 are RL, the state value of the new circuit is L. Otherwise, the state value of the new circuit is X. When level 3, the state value of the new circuit is determined by the old state value and driving force. The state of the driving force is
There are three cases: when all level 1 driving forces are CH, when all level 1 driving forces are CL, and when both CL and Cl.

(Refer to the logical value explanation chart in Figure 6) When the old state value is H, if the driving force is CH, then H1, if the driving force is CL, then X, if both, then X, and the old state value is L. If the driving force is CH, then X17, and the driving force is CL.
If so, then if both are X, when the old state value is It becomes X.

Also, if the old state is an absolute value, when the driving force is CH, it is H1, when the driving force is CL, it is X, when the old state value is ZL, if the driving force is CH, it is X, and when the driving force is CL If so, it becomes L. Note that if the driving force is both CL and CH, both will be X regardless of the old state value. In other words, when the old state value is H, if the driving force is CHX, then H
, CLX, then X, when the old state value is L, if the driving force is CHX, then X, if the driving force is CLX, and if the old state value is Z, then the driving force is CHX If ZH1 driving force is CLX and XL, and the old state value is X, then the driving force is CHX and X, CLX is X, and the old state value is Z.
When the driving force is CHX when the old state value is ZL, it becomes X when the driving force is CHX, and ZL when the old state value is ZL.

Note that it becomes X when both CHX and CLX exist, regardless of the old state value.

When the strongest driving force in group 1 and the strongest driving force in group 2 are at the same level - If the strongest driving force is level 1 If all the driving forces at level l are DH or DHX, then the driving force at level 1 is H When all the driving forces are DL or DLX, it is L. Otherwise, it is When the driving force is level 3, the evaluation value is determined based on three states (see the logic explanatory diagram in FIG. 8). When all level 2 driving forces are H or CHXO, (1
0) Old state values are H and L.

When Z, X, ZH, ZL, it becomes H, X, H, X, H, X. Also, when the level 2 driving force is all CL or CLX (
20), the old state values are H, L, and Z.

If X, ZH, ZL, the evaluation values are X, L, LX, X,
Let it be L. In other cases, all values are set to X regardless of the old state value. Also, the oldest level of driving force is level 4.
In the case of , when all level 2 driving forces are φ, the previous net value is held.

A net value, ie, a state value, is determined in process ST2 using the old state value and each driving force described above. Subsequently, it is determined whether or not the net value has changed (Sr3).

When it is determined that the net value has changed, it is then determined whether all switching elements whose gates are connected to the net for which the net value was calculated have been processed (Sr4).
do.

If this is not done for all switching elements, that is, if there are elements to be processed, then the driving force passing through the selected switching elements is evaluated (Sr1).

The gate to which the aforementioned net value is applied becomes conductive or non-conductive depending on the net value.

FIG. 9 is a diagram explaining the states of the switching elements. If the net value of the gate connected to the net is H, the state of the MO3 circuit, which is a switching element, becomes conductive. If it is L, it will be in a non-conducting state, and if it is Z or X, it will be in an unknown state. The driving force passing through the element changes depending on whether the switch is conductive or nonconductive. That is, if it becomes conductive, a new mutual driving force will be added to the net value connected to the source and drain sides, and if it becomes off, the previous state will no longer be added. This driving force is similar to that obtained by process 5TII, which will be described later.

The driving force passing through the switching element taken out in process ST5 is evaluated, and then it is determined in ST6 whether or not the part power has changed as a result. If there is no change, the determination is performed again from ST4.

On the other hand, when it is determined in determination ST6 that the driving force has changed, processing ST7 is performed to register the change in driving force. Then, the process is repeated from determination ST4. By repeating this process, the gate is turned on and off in response to a change in the driving force of the input terminal, and the change in the driving force caused by the turning on and off of the switching element is finally registered.

If all the switching elements connected to the above-mentioned net have been processed (all have been processed), then in step ST3, all the switching elements whose sources or drains are connected to the net whose net value has changed are determined in step ST3. Process ST9 of turning on the determination flag to determine whether
Then, based on the flag, it is determined whether or not all processing has been performed. If all the processing has been completed (has been done), a determination step 5TI2 is made to determine whether or not there is a change in the registered driving force. If there is no change in the registered driving force, the process ends. On the other hand, if there is a change in the registered driving force (there is), processing is performed as if the driving force has changed again from that point.
Similar processing is repeated from TI.

On the other hand, in process ST2, the net value driven by the driving force is evaluated, and in step ST3, it is determined whether the net value has changed. Sr1 is performed to turn on a flag indicating whether all processing has been performed for other switching elements whose sources or drains are connected to , and then it is determined whether the flag is on, that is, whether all processing has been performed (STIO) do. When it is determined in this determination 5TIO that all processing has not been performed, the driving force passing through the switching element is subsequently evaluated (STII).

FIG. 10 is an overall explanatory diagram of the driving force. Taking the switching element E as an example, the driving force → of the driving force a - d that has passed through the switching element A and the switching element D is transmitted from the source side to the drain side of the switching element E. (It is assumed that the driving force transmitted from the drain side of switching element E is not transmitted from the source side to the drain side of E again.) Also, the calculation of the driving force transmitted from the source to the drain side of E is from driving force a to d. and the state value α of the net. First, in order to find this resultant force, the levels of all the driving forces transmitted from other switching elements are found.

When the strongest level is level 1 and there is a driving force DH in which all the driving forces at level 1 are determined to be driving forces in the H direction, the resultant force is DH.

When all the driving forces at level 1 are driving forces in the H direction and only the possible driving force DHX, the resultant force is DHX.

When there is a driving force DL in which all level 1 driving forces are determined to be driving forces in the L direction, the resultant force is DL.

When all the driving forces at level 1 are driving forces in the L direction and only the possible driving force DHL, the resultant force is DHL.

The driving force at level 1 is in both the H direction and the L direction, and the driving forces DL and DH are determined for both directions.
When there is, the resultant force is DC.

When the level 1 driving force is in both the H direction and the L direction, but there is no determined driving force DH or DL in both directions, the resultant force is DCX.

When the strongest level is level 2, it is the same as level 1. That is, RH → RH RHX → RHX RL -> RL RHL → RHL RL and RH → RC RH or RL = +' RCX Also, when the strongest level is level 3, all driving forces transmitted from other switching elements The resultant force is determined by the net state value α.

FIG. 11 is a driving force explanatory chart.

If the type of driving force is only in the H direction, the state of the circuit is α
If it is H, it is CH, if it is X, it is CCX, and if it is H2, it is CH. In addition, if there are only types of driving force in the L direction, CL when the circuit state value α is L, and CC when the circuit state value α is X.
When X, LZ, it is assumed to be CL. Also, the n class of driving force is H and L.
If both are determined, CC is set only when the circuit state value α is X. In addition, both H and L are undetermined, and furthermore, H
When the direction is determined and the L direction is determined, or when the L direction is determined and the H direction is not determined, CCx is set when the state value α of the circuit is X.

Note that in the diagram of FIG. 11, d represents a case that is impossible as a simulation state.

Furthermore, when the strongest level is level 4 (drive is not transmitted from anywhere), the resultant force is determined by the net state value α. That is, the state value α of the circuit is HL, Z, X, H2,
The driving force required for LZ is CH.

TL, I, CC, C) IX, TLX.

The driving force passing through the switching element is evaluated by the method described above. Then, similarly to process ST5, process 5TII
A determination 5T13 is made as to whether or not the driving force has changed, and if there is no change (no change), the process is repeated from step 5TIO. Further, if the driving force changes (has occurred), the change in the driving force is registered (ST14). Then, the process is repeated from determination 5TIO.

FIG. 4 is an explanatory diagram of the connection configuration. In the case where the switch SX has one circuit and two contacts, and one is connected to the power supply Vcc and the other is grounded, a case will be explained in which this switch has been connected to the blend level and changed to the power supply Vcc side. In this case, the driving force of the switch. Since it is connected to the power supply, it becomes D) ((when it was connected to the ground side, it was DL).

Therefore, by changing this switch at this time, D+o+D
oll, Dzo and Niri. Evaluate the intersection where is connected, that is, the net value of net A (Process 5T2 in Figure 2)
. As explained in the net value evaluation ST2, the maximum level driving this net A is DH (level 1), so the net A becomes H.

Then, in the other switch elements Sl, S2, and 33, the switch 32. S3 is the gate that should be turned on, that is, H
Levels have been added. However, since one side of S3 is open and the other side of switch S2 is also X (indeterminate), the level of the driving force of Dzn is lower than the driving force of the switch, so the net value to the net becomes 4. Net A
Since the net value of has changed, in the process shown in FIG. 2, a process ST5 is executed to evaluate the driving force passing through the switching element taken out. That is, since the switching element S5 has changed from off to on, the corresponding driving forces Dso and Ds. Evaluate. Since only the gate of the switch element S5 is connected to the net A, the evaluation ends with the evaluation of the driving force of this one element. In addition, at this time D,
When the driving force of n, D q+ changes, the driving force is of course registered in step ST7 shown in FIG.

Also, net A has switches SL, S2. S3 is connected. At this time, the switches S2 and 33 are on, so the driving force passing through these switching elements is evaluated (S
TII). At this time, the target of evaluation is the driving force D2
1. Di□. This evaluation further changes the net value of net B.

Also, since switch S4 is connected to net)B, D4+ is similarly evaluated.

The driving force is sequentially determined in the order described above, and the evaluation value of the entire circuit system can be determined.

As described above, according to the present invention, 19 types of driving force are defined, and the 19 types of definitions are used to evaluate the driving force and the net value. Conventionally, when a simple switching element is used, it is determined only by the relationship between the gate, that is, the input and the output, but according to the present invention, the value of the driving force is set between, for example, the source and drain of the switching element. , and the driving force in each direction determines how to drive in each direction, and it is possible to completely perform logic simulation in the MO3 circuit. In particular, the basics of the 19 types of definitions are the highest level driving force connected to the power supply or ground, the second driving force connected to the power supply or ground level via a resistor, and the unique driving force of MOS transistors. The drive level of electrostatic charge in the OFF state is basically divided into four types: no drive force at all. This means that, for example, if it is the highest level, it will be the highest level value even if it is connected to the net through a resistor or due to electrostatic charge. This expresses the fact that the level naturally decreases. In addition, even in a simple net value, that is, a state value, the expression changes depending on each state, such as high level, low level, high impedance, high impedance or high level, high impedance or low level, and at which level It is made clear what kind of drive is applied to reach that level. This allows the value of each net to be clearly defined.

〔Effect of the invention〕

As described above, according to the present invention, by evaluating the driving force and its net value, it is possible to reliably perform a logic simulation of a switching element. Also, M
It is possible to perform high-speed timing verification that also takes into account the influence of electrostatic charge, which is specific to the logic of the O3 circuit.

[Brief explanation of drawings]

FIG. 1 is a principle block diagram of the present invention; FIG. 2 is a processing flowchart of an embodiment of the present invention; FIG. 3 is an explanatory diagram of symbols used to explain the present invention; FIG. 4 is an explanatory diagram of a connection configuration; Figure 5 is an explanatory chart for levels and groups, Figures 6 and 7
8 is a logic explanatory diagram, FIG. 9 is a state explanatory diagram, FIG. 10 is a state explanatory diagram, FIG. 11 is a driving force explanatory diagram, and FIG. 12 is a driving force explanatory diagram. 1... Net evaluation means, 2... Driving force evaluation means, 3... Control means. Logical value explanatory diagram (Figure) Logical value explanatory diagram (Figure) Figure Status explanatory diagram (Figure 0) Figure 0

Claims (1)

[Scope of Claims] 1) Net evaluation means (1) that divides the driving force to the connection point to which the switching element is connected into two according to the direction and evaluates the net value of the connection point; and the net evaluation means (1). a driving force evaluation means (2) for determining the driving force of a switching element different from the switching element whose gate is connected to the connection point when the net value obtained by the above changes; and by the driving force evaluation means (2). Switching characterized by comprising a control means (3) for operating the net evaluation means (1) and the driving force evaluation means (2) again based on the obtained driving force to obtain a final net value and driving force. Element logic simulation method. 2) The driving force is a current value or a voltage value flowing through each circuit element connected to the connection point, and the net value is a relaxation of the driving force connected to the connection point. 1. Logic simulation method for the switching element according to 1. 3) The switching element logic simulation method according to claim 1, wherein the control means (3) repeatedly operates the net evaluation means (1) and the driving force evaluation means (2) a plurality of times.