JP2008113016A - Semiconductor integrated circuit, and method of designing same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the problem that a power source voltage supplied to a cell on a clock path decreases to cause clock skew, since a resistance component is contained in a power supply wiring of a semiconductor integrated circuit. <P>SOLUTION: The semiconductor integrated circuit includes a plurality of cells disposed in a two-dimensional region, a power supply wiring 52 arranged in an upper wiring layer of the two-dimensional region so that the power is supplied to the cells through a contact via, and a reinforcement power supply wiring 56 which is arranged in the upper wiring layer of the two-dimensional region independently of the power supply wiring, the voltage higher than that of the power supply wiring being applied thereto. Further, the circuit has a voltage converter 57 disposed in the two-dimensional region so that the voltage in the reinforcement power supply wiring 56 is lowered as far as the power supply voltage to be fed to the power supply wiring. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a semiconductor integrated circuit and a design method thereof, and more particularly to a semiconductor integrated circuit designed in consideration of IR-drop of a power supply wiring and a design method thereof.

  Many semiconductor integrated circuits including a logic circuit operate in synchronization with an externally supplied clock signal or an internally generated clock signal based on an externally supplied signal. In general, a semiconductor integrated circuit includes a plurality of flip-flops and a circuit that generates a clock signal supplied to each flip-flop based on a given clock signal (hereinafter referred to as a clock circuit). In order for the semiconductor integrated circuit to operate correctly, it is necessary to correctly supply a clock signal to each flip-flop. In order to reduce the power consumption of the semiconductor integrated circuit, it is effective to stop the supply of the clock signal to the circuit block that is not operated. For this reason, the configuration of the clock circuit and the method for supplying the clock signal are recognized as important issues in the design of the semiconductor integrated circuit.

  When designing a logic circuit, a cell-based design in which rectangular cells corresponding to logic elements are arranged in a two-dimensional region is widely used. In particular, in the cell-based design, a cell having a common height (standard cell) is often used in order to facilitate cell arrangement. FIG. 19 is a diagram showing a layout result of a conventional semiconductor integrated circuit. In FIG. 19, a rectangular area with the letter C represents one cell (standard cell). The cells are arranged with the same height in a plurality of belt-like regions 91 provided in parallel in the two-dimensional region. A power supply wiring 92 for supplying power to each cell is provided between the two strip regions 91. The power supply wiring 92 includes a power supply wiring 92a to which the power supply voltage VDD is applied and a power supply wiring 92b to which the ground voltage VSS is applied. These two types of power supply wirings 92a and 92b are alternately arranged in a two-dimensional region where the strip-like regions 91 are arranged.

  In recent semiconductor integrated circuits, since the power supply wiring contains a resistance component, when power is supplied to each cell via the power supply wiring, the voltage supplied to each cell is supplied from the outside of the semiconductor integrated circuit. The phenomenon that the voltage becomes lower than the voltage (hereinafter referred to as IR-drop) is a problem. FIG. 20 is a diagram illustrating how IR-drop occurs. FIG. 20 shows the distribution of the power supply voltage supplied to each cell included in the semiconductor integrated circuit 93 when a 3.0 V power supply voltage is supplied from the power supply terminal 94 of the semiconductor integrated circuit 93. Even if a power supply voltage of 3.0 V is supplied from the power supply terminal 94, the power supply wiring 95 includes the resistance component 96. Therefore, each cell included in the semiconductor integrated circuit 93 has a power supply voltage lower than 3.0 V. Only supplied. For example, the cell 97 is only supplied with a power supply voltage of about 2.7V.

  The reason why such IR-drop occurs is that when the cell operates and the value of the output signal of the cell changes, current flows from the power supply wiring to the terminal of the transistor included in the cell, and from the outside of the semiconductor integrated circuit This is because the supplied voltage drops by an amount corresponding to the product of the flowing current and the resistance component of the power supply wiring when it reaches each cell. In particular, when an IR-drop occurs in the power supply voltage supplied to a cell on the clock path, the delay time during actual operation of the cell on the clock path is different from the delay time when no IR-drop occurs. Thus, a clock skew exceeding the amount assumed at the time of circuit design occurs. When such a clock skew occurs, there is a possibility that the circuit malfunctions.

Conventionally, various techniques have been known for the arrangement of cells included in a semiconductor integrated circuit and IR-drop countermeasures. Among these, as a technique related to the present invention, for example,
There exists what was described in patent documents 1-3. Patent Document 1 describes an automatic placement design method and apparatus that performs timing analysis after placement and routing, and automatically inserts, replaces, and deletes delay cells when timing constraints are not satisfied. Patent Document 2 describes a method in which a clock buffer for supplying a clock signal to a plurality of cells is arranged at a position closer to the power supply wiring than any of the plurality of cells. In Patent Document 3, timing analysis and power supply wiring voltage drop analysis are performed after placement and wiring. If there is a voltage drop, a voltage drop countermeasure element placed together with a logic element and a voltage supply I / O are placed between them. A layout apparatus and method for wiring reinforcing power supply wiring is described.
Japanese Patent Laid-Open No. 7-14927 Japanese Patent Laid-Open No. 11-251439 JP 2002-110802 A

  However, in recent semiconductor integrated circuits, as the miniaturization progresses, the width of the power supply wiring becomes narrower, so that the resistance value per unit length of the power supply wiring increases and IR-drop is likely to occur. In addition, with the increase in circuit scale and voltage, clock skew is likely to occur. For this reason, in recent semiconductor integrated circuits, it is necessary to suppress the occurrence of clock skew caused by IR-drop at a higher level than before.

  Therefore, an object of the present invention is to provide a semiconductor integrated circuit in which generation of clock skew due to IR-drop is suppressed, and a design method thereof.

  A first invention for solving the above-described problem is provided with a plurality of cells and a plurality of wirings, and a cell placement prohibition region centered on each cell is set in all or a part of the cells on the clock path. The cell performing the logic operation is a semiconductor integrated circuit arranged in a portion where the cell arrangement prohibition area is not set.

  In this case, a cell placement prohibition area centered on a cell arranged in a certain band-shaped area may overlap with the band-like area immediately above and immediately below with a width equal to or greater than the width of the cell. It is good also as overlapping with the width | variety of 3 times or more of this width | variety.

  In addition, a cell group prohibition region is set for each cell group in all or part of a cell group consisting of a plurality of cells closely arranged in the same band-like region. Also good.

  In addition, a capacity cell may be arranged in the cell arrangement prohibition area, and more preferably, the cell arrangement prohibition area centered on the cell arranged in a certain band area is immediately above and immediately below the band area. The overlapping capacity cells may be arranged in the overlapping portion.

  2nd invention arrange | positions all or one part of the cell on a clock path | route, arrange | positions the dummy cell larger than a cell virtually in the arrangement position, and arrange | positions the non-arranged cell in the position where the dummy cell is not arrange | positioned A method for designing a semiconductor integrated circuit.

  According to a third aspect of the present invention, a cell is arranged, and a cell arrangement prohibition area larger than the cell is set at the cell arrangement position for all or a part of the cells on the clock path, and the cell is arranged in the cell arrangement prohibition area. This is a method for designing a semiconductor integrated circuit, in which cells that perform a logical operation are rearranged outside the cell placement prohibited area.

  4th invention produces | generates the composite cell containing each cell and a capacity | capacitance cell about all or one part of the cell on a clock path | route, arrange | positions the produced | generated composite cell, and a composite cell arrange | positions the cell which is not arranged This is a method for designing a semiconductor integrated circuit, which is arranged at a position that is not provided.

  In the second to fourth aspects of the invention, a cell group composed of a plurality of cells arranged closely in the same band-like region may be handled as one cell.

  According to a fifth aspect of the present invention, the degree to which the power supply voltage supplied to the cell drops due to the resistance of the power supply wiring is obtained for all or part of the cells on the clock path by arranging the cells. This is a method for designing a semiconductor integrated circuit, in which when a predetermined criterion is not satisfied, a cell arranged in the vicinity of a cell on the clock path is rearranged at a position away from the cell on the clock path.

  A sixth invention includes a plurality of cells, a first power supply wiring for supplying power to all or a part of the cells on the clock path, and a second power supply wiring for supplying power to the remaining cells. The first power supply wiring is a semiconductor integrated circuit provided separately from the second power supply wiring.

  In the seventh invention, a plurality of cells, a power supply wiring for supplying power to the cells, a reinforcing power supply wiring to which a voltage higher than the power supply wiring is applied, and a voltage on the reinforcing power supply wiring should be supplied to the cells The semiconductor integrated circuit includes a voltage conversion unit that drops the power supply voltage and applies it to the power supply wiring. In this case, the voltage conversion unit is configured by, for example, a power transistor. Also, the power supply wiring for supplying power to the cells and the reinforcing power supply wiring to which a higher voltage than the power supply wiring is applied are arranged in the same wiring layer in the upper layer in the two-dimensional region where a plurality of cells are arranged. Also good.

  According to the first aspect of the invention, since a cell that performs a logic operation is not arranged in the vicinity of the cell on the clock path, the point that the cell on the clock path is connected to the power supply wiring is the logic operation. The cell to be performed is separated from the point connected to the power supply wiring by a certain distance or more. For this reason, the cells on the clock path are not easily affected by IR-drop that occurs when a cell that performs a logic operation operates. Therefore, it is possible to prevent a problem that the power supply voltage supplied to the cells on the clock path drops when other cells operate, the clock skew occurs, and the circuit malfunctions.

  If the capacitor cell is provided, the power supplied via the power supply wiring can be stabilized, so that the above problem can be prevented more effectively.

  According to the second to fourth aspects of the invention, it is possible to design a semiconductor integrated circuit characterized in that no cell that performs a logic operation is disposed in the vicinity of a cell on the clock path. Further, the processing can be simplified by collectively arranging the dummy cells, setting the cell placement prohibited area, placing the capacity cells, etc. for the cells on the clock path.

  According to the fifth aspect of the invention, it is possible to design a semiconductor integrated circuit in which the occurrence of clock skew due to IR-drop is suppressed without moving cells on the clock path.

  According to the sixth aspect, even when a cell other than the cell on the clock path operates, the influence does not reach the power supply wiring for supplying power to the cell on the clock path. Generation of clock skew due to IR-drop can be suppressed.

  According to the seventh aspect, it is possible to effectively suppress the IR-drop generated at the center portion of the chip and to suppress the occurrence of clock skew due to the IR-drop.

(First embodiment)
In the first embodiment of the present invention, a semiconductor integrated circuit that suppresses the occurrence of clock skew caused by IR-drop and a design method thereof will be described. FIG. 1 is a diagram showing a layout result of the semiconductor integrated circuit according to the present embodiment. The semiconductor integrated circuit shown in FIG. 1 includes a plurality of cells (rectangular regions with a letter C) and wiring that connects the cells. In FIG. 1 and the subsequent drawings, hatched cells represent cells on the clock path, and wirings connecting the cells are appropriately omitted for simplification of the drawings.

  The cells shown in FIG. 1 are standard cells having a common height, and are arranged with the same height in a plurality of strip-like regions 11 provided in parallel in a two-dimensional region. A power supply wiring 12 for supplying power to each cell is provided between the two strip regions 11. The power supply wiring 12 includes a power supply wiring 12a to which the power supply voltage VDD is applied and a power supply wiring 12b to which the ground voltage VSS is applied. These two types of power supply wirings 12a and 12b are alternately arranged in a two-dimensional region where the strip-like regions 11 are arranged. In order to reduce the chip size of the semiconductor integrated circuit and reduce the manufacturing cost, it is desirable to arrange the cells as close as possible. However, depending on the condition of the wiring connecting the cells, there is a gap between the cells. Sometimes it happens.

  In the semiconductor integrated circuit shown in FIG. 1, an area where a cell that performs a logic operation around each cell cannot be placed (hereinafter referred to as a cell placement prohibited area) is set in all or part of the cells on the clock path. The cell that performs the logic operation is arranged in a portion of the band-like region 11 excluding the cell arrangement prohibition region.

  Hereinafter, a description will be given of a case where a cell placement prohibition region centered on the cell 10 is set for the cell 10 on the clock path arranged in the nth (n is an integer, the same applies hereinafter) band-like region 11. . Cell 10 is any type of cell on the clock path. In general, a cell on a clock path is required to be less susceptible to IR-drop than other cells. Therefore, in the semiconductor integrated circuit according to the present embodiment, a cell that performs a logic operation is not arranged in the cell arrangement prohibited area centering on the cell 10.

For example, in the semiconductor integrated circuit shown in FIG.
(1) a first rectangular area occupied by the cell 10,
(2) a second rectangular area occupied by the moved cell when the cell 10 is translated in the height direction of the cell to the (n−1) th band-shaped area;
(3) a third rectangular area occupied by the moved cell when the cell 10 is translated in the height direction of the cell to the (n + 1) th band-shaped area;
(4) a fourth rectangular area sandwiched between the first and second rectangular areas; and (5) a combined area of the fifth rectangular area sandwiched between the first and third rectangular areas. Yes. For this reason, in this semiconductor integrated circuit, cells that perform a logic operation are not arranged in the second and third rectangular regions. This is shown in FIG. 1 by the fact that no cells that perform logic operations are placed directly above and below the cell 10.

Various methods including the method shown in FIG. 1 are conceivable as the method for setting the cell placement prohibited area. If the height of the cell 10 is H, the width is W, and the width of the power supply wiring 12 is h, for example, the cell placement prohibited area 13 shown in FIG. In this case, the widths A and B shown in FIG. 2 are determined to appropriate values. The cell placement prohibition area 13 is
(1) a first rectangular region having a height H and a width (W + 2B) at the same position as the cell 10 in the n-th strip region;
(2) a second rectangular region having a height H and a width A in which the position in the width direction of the cell 10 and the cell 10 is equal in the (n-1) th band-shaped region;
(3) a third rectangular region having a height H and a width A in which the position in the width direction of the cell 10 and the cell 10 is equal in the (n + 1) th band-shaped region;
(4) a height h sandwiched between the first and second rectangular regions, a fourth rectangular region having a width (W + 2B), and (5) a height h sandwiched between the first and third rectangular regions, The fifth rectangular area having the width (W + 2B) is combined. Since the cells cannot be arranged in the area where the power supply wiring 12 is arranged, the fourth and fifth rectangular areas need not be included in the cell arrangement prohibited area 13, and even if included, The width may be arbitrary (for example, the width A may be used).

  The widths A and B are determined so that at least one is a positive number. When the width A is smaller than the width (W + 2B), the cell placement prohibited area 13 has a cross shape (area 13a) as shown in FIG. 2A. When the width A is larger than the width (W + 2B) Becomes H-type (region 13b) as shown in FIG. When the width A is equal to or greater than the width W of the cell 10, the cell placement prohibited area 13 overlaps the (n−1) th and (n + 1) th band-shaped areas 11 with a width equal to or greater than the width of the cell 10. When the width B is equal to or larger than the width W of the cell 10, the cell placement prohibited area 13 overlaps the nth band-shaped area 11 with a width that is three times or more the width of the cell 10.

  The layout result shown in FIG. 1 is obtained when the width A is W (the width of the cell 10) and the width B is 0. In addition to this, for example, when the width A is 2 W and the width B is 0, the layout result shown in FIG. 3A is obtained, and when both the width A and the width B are W, The layout result shown in FIG. 3B is obtained. When the width A is 2W and the width B is W, the layout result shown in FIG. 3C is obtained. In any of these layout results, no cell that performs a logic operation is arranged in the cell arrangement prohibited area centered on the cell 10.

  A plurality of cells (hereinafter referred to as cell groups) connected in a predetermined manner may be included on the clock path of the semiconductor integrated circuit. A typical example of the cell group is a delay cell group configured by connecting a plurality of delay cells in series (see FIG. 4 described later). When the cells are arranged, the cell group is arranged as one lump within one band-like region, and the cells included in the cell group are arranged closely within one band-like region. The reason why the cells included in the cell group are closely arranged in the same band-like region is to minimize the influence of the delay of the wiring connecting the cells on the delay time of the cell group.

  Even when the cell group is on the clock path, it is desirable to set a cell disposition prohibition region for the cells included in the cell group, as in the layout results shown in FIGS. However, as described above, since the cells included in the cell group are closely arranged in one band-like region, it is not possible to set a cell placement prohibition region centered on each cell for each cell. Therefore, regarding the cell group on the clock path, the whole cell group is regarded as one cell, and is handled in the same manner as one cell on the clock path.

  Hereinafter, a case will be described in which a cell placement prohibition region centered on the delay cell group 14 is set for the delay cell group 14 (FIG. 4) placed on the clock path and placed in the nth band-like region. As shown in FIG. 4A, the delay cell group 14 is a circuit in which a plurality (three in FIG. 4) of delay cells are connected in series. If the number of delay cells included in the delay cell group 14 is D, the height of each delay cell is H, and the width is W, the arranged delay cell group 14 has a height as shown in FIG. Occupies a rectangular area of H and width DW.

  For the delay cell group 14, a cell placement prohibition region in which the delay cell group 14 is applied to the cell 10 portion may be set in the cell placement prohibition region 13 shown in FIG. In other words, for the delay cell group 14, after the widths A and B are appropriately determined, a cell placement prohibited area having the width W as the width DW may be set in the cell placement prohibited area 13 shown in FIG. .

  When setting the cell placement prohibition region as described above for the delay cell group 14, for example, when the width A is DW (the width of the entire delay cell group 14) and the width B is 0, FIG. The layout result shown in a) is obtained. Further, when the width A is (D + 2) W and the width B is 0, the layout result shown in FIG. 5B is obtained, and when the width A is (D-1) W and the width B is 0. 5C, the layout result shown in FIG. 5C is obtained. When the width A is DW and the width B is W, the layout result shown in FIG. 5D is obtained, and the width A is (D + 2). When W and width B are set to W, the layout result shown in FIG. 5E is obtained. In any of these layout results, no cell that performs a logic operation is arranged in the cell arrangement prohibited area centering on the delay cell group 14.

  Next, as shown in FIG. 1, FIG. 3, and FIG. 5, the effect of not placing a cell that performs a logic operation in the vicinity of a cell (or cell group) on the clock path will be described. When the cell C performing the logic operation operates and the value of the output signal of the cell changes, the charge stored in the power supply wiring near the cell C, the power supply connection part (VDD part and VSS part) in the cell C, etc. , Current flows from the power supply wiring to the cell C. At this time, the amount of current flowing through the power supply wiring is maximized at a portion where the cell C is connected to the power supply wiring (hereinafter referred to as a power supply point for the cell C). For this reason, when the cell C that performs the logic operation and the cell C ′ on the clock path are arranged at positions facing each other across a certain power supply wiring, the power supply point for the cell C and the power supply for the cell C ′ Due to the proximity of the supply point, cell C ′ is susceptible to IR-drop when cell C is activated. The same applies to the case where the cell C performing the logic operation and the cell C ′ on the clock path are arranged adjacent to each other in the same band-like region.

  Under such circumstances, in order to prevent the cell C ′ on the clock path from being affected by the IR-drop, the power supply point for the cell C ′ is sufficiently separated from the power supply point for the cell C. Just keep it. In the semiconductor integrated circuit according to the present embodiment, since a cell that performs a logic operation is not disposed in the vicinity of a cell on the clock path, the power supply point for the cell on the clock path is a cell that performs a logic operation. It is more than a certain distance away from the power supply point. For this reason, the cells on the clock path are not easily affected by IR-drop that occurs when a cell that performs a logic operation operates. Therefore, according to the semiconductor integrated circuit according to the present embodiment, when other cells operate, the power supply voltage supplied to the cells on the clock path drops, clock skew occurs, and the circuit malfunctions. Can be prevented.

  In the semiconductor integrated circuit according to the present embodiment, what cell placement prohibition region is set for a cell (and a cell group) on the clock path becomes a problem. Increasing the size of the cell placement prohibition region can increase the effect of suppressing the occurrence of clock skew caused by IR-drop, while increasing the chip size and increasing the circuit manufacturing cost. On the other hand, if the size of the cell arrangement prohibited area is too small, the above effect cannot be sufficiently improved. Therefore, when determining the shape and size of the cell placement prohibited area for the cells on the clock path, the influence of the circuit power supply voltage, IR-drop, timing constraints set during circuit design, etc. Therefore, it is necessary to determine an appropriate shape and size. Further, in order to separate the power supply point for the cell on the clock path from the power supply point for the cell performing the logic operation, the power supply point is set for the cell on the clock path arranged in the nth band-shaped region. It is not necessary for the cell placement prohibited area to overlap the band-shaped area before the (n−2) th and the band-shaped area after the (n + 2) th. The cell arrangement prohibition area 13 shown in FIG. 2 is devised in consideration of such points.

  In the semiconductor integrated circuit according to the present embodiment, a cell placement prohibition region may be set for all cells (and cell groups) on the clock path, or cells (and A cell placement prohibited area may be set for a part of the cell group. When selecting a cell for which a cell placement prohibited area is set from all the cells on the clock path, it is only necessary to select a cell after setting some reference. For example, a cell whose cell delay time is equal to or greater than a predetermined threshold value may be selected from all the cells on the clock path, and the cell placement prohibited area may be set only for the selected cell.

  Next, two types of methods for designing the semiconductor integrated circuit according to the present embodiment will be described. FIG. 6 is a flowchart showing a first design method of the semiconductor integrated circuit according to the present embodiment. This first design method is typically executed using an EDA (Electronic Design Automation) system, which is a semiconductor integrated circuit design apparatus.

  In the method shown in FIG. 6, first of all, cells on the clock path are arranged among the cells included in the circuit to be designed (step S101). The arrangement position of the cells on the clock path is determined based on the floor plan information of the clock circuit and the like before determining the arrangement positions of other cells. More specifically, in step S101, a cell in which a cell placement prohibition region is to be set is selected from all the cells on the clock path, and the selected cells are parallel to each other in the two-dimensional region of the semiconductor integrated circuit. It arrange | positions in height in the several strip | belt-shaped area | region provided. In step S101, all of the cells on the clock path may be selected or some of them may be selected.

  Next, a dummy cell larger than each cell is virtually arranged at the position where the cell is arranged in step S101 (step S102). The shape and size of the dummy cells arranged in step S102 are made to coincide with the shape and size of the cell arrangement prohibited area centered on each cell.

  For example, in the case where the cell placement prohibition region is set by the same method as in FIG. 2 for the cell 15 having the height H and the width W shown in FIG. When the width B is set to 0, in step S102, the dummy cell 16b having a height (3H + 2h) and a width W shown in FIG. The height h is the width of the power supply wiring. In the same case, when the width A is 2 W and the width B is 0, a dummy cell 16 c having an H shape shown in FIG. 7C is arranged at the same position as the cell 15. Further, in the case where the cell placement prohibited area is set by the same method as in FIG. 2 for the delay cell group 17 composed of D delay cells having the height H and the width W shown in FIG. Is DW (the width of the entire delay cell group 17) and the width B is 0, in step S102, the height (3H + 2h) and the width DW shown in FIG. Dummy cells 18b are arranged. In the same case, when the width A is (D + 2) W and the width B is 0, the dummy cell 18c having the H shape shown in FIG. Be placed. The same applies to the case where a cell placement prohibition region having a shape other than the above is set for a cell (or cell group) on the clock path.

  Next, among the cells included in the circuit to be designed, the cells that are not arranged in step S101 are arranged (step S103). In step S103, no cell is placed in an area where dummy cells are already placed. Therefore, in step S103, the non-arranged cells are arranged at the same height in a portion excluding the area where the dummy cells are arranged in the plurality of band-like areas where the cells are arranged in step S101. As described above, according to the first design method shown in FIG. 6, the cell for performing the logic operation is not arranged in the vicinity of the cell on the clock path. A circuit can be designed.

  FIG. 9 is a flowchart showing a second design method of the semiconductor integrated circuit according to the present embodiment. Similar to the first design method (FIG. 6), this second design method is typically performed using an EDA system.

  In the method shown in FIG. 9, first, all the cells included in the circuit to be designed are arranged (step S201). More specifically, in step S201, all the cells included in the circuit to be designed are arranged at the same height in a plurality of strip-like regions provided in parallel in the two-dimensional region.

  Next, for the cells on the clock path among the cells arranged in step S201, a cell arrangement prohibition area larger than each cell is set at the arrangement position of each cell (step S202). More specifically, in step S202, a cell in which a cell placement prohibited area is to be set is selected from all the cells on the clock path. For example, the cell placement prohibited area shown in FIG. 13 is set. In step S202, all of the cells on the clock path may be selected or some of them may be selected.

  Next, the cell that performs the logical operation and is arranged in the cell arrangement prohibited area set in step S202 is rearranged outside the cell arrangement prohibited area (step S203). More specifically, in step S203, the cell that performs the logical operation and is arranged in the cell arrangement prohibited area is rearranged in a portion excluding the cell arrangement prohibited area in the band area where the cell is arranged. In step S203, only the cells arranged in the cell placement prohibited area may be rearranged, or other cells may be rearranged as the cells placed in the cell placement prohibited area are rearranged. It is good also as arranging. As described above, according to the second design method shown in FIG. 9, the cell for performing the logic operation is not arranged in the vicinity of the cell on the clock path. A circuit can be designed.

  The first and second design methods have the following effects. As a method for prohibiting cells from being placed in a specific region when placing cells included in a circuit to be designed, a method of setting a region called a placement blockage has been conventionally known. This arrangement blockage corresponds to a cell arrangement prohibition area in the semiconductor integrated circuit according to the present embodiment, but in the conventional method, the arrangement blockage is individually set for each of the areas where cell arrangement is prohibited. There is a need to. On the other hand, in the first and second design methods, cell placement prohibition areas are collectively set for all or part of the cells on the clock path. Therefore, according to the first and second design methods described above, the placement blockage is not individually set for each of a large number of cells on the clock path, and the cell is placed in the vicinity of the cell on the clock path. The semiconductor integrated circuit according to this embodiment can be designed in which no cell that performs a logic operation is arranged.

  The first and second design methods can be used in combination with a method for prohibiting cells from being placed in a specific region using the placement blockage. That is, in the first and second design methods described above, before placing a cell, a placement blockage is set in an area where the placement of the cell should be prohibited, and when placing a cell, the placement blockage within the set placement blockage is set. It is good also as not arrange | positioning a cell.

(Second Embodiment)
In the second embodiment of the present invention, a semiconductor integrated circuit that suppresses the occurrence of clock skew caused by IR-drop and a design method thereof will be described. FIG. 10 is a diagram showing a layout result of the semiconductor integrated circuit according to the present embodiment. The semiconductor integrated circuit shown in FIG. 10 is obtained by adding capacity cells 21a and 21b to the semiconductor integrated circuit (FIG. 1) according to the first embodiment. Among the constituent elements of the present embodiment, the constituent elements other than the capacity cells 21a and 21b are the same as those in the first embodiment, and therefore the same reference numerals are given and the description thereof is omitted.

  In FIG. 10, cell 10 is any type of cell on the clock path. For the cell 10, in the cell placement prohibited area 13 shown in FIG. 2, a cell placement prohibited area is set in which the width A is W (the width of the cell 10) and the width B is 0. No cell that performs a logic operation is arranged. In the semiconductor integrated circuit according to the present embodiment, the capacitor cells 21a and 21b are arranged in the cell arrangement prohibited area. More specifically, when a cell placement prohibition region centered on the cell 10 is set for the cell 10 on the clock path arranged in the nth band-like region 11, (n-1) The capacity cell 21a is arranged in the position where the cell 10 and the position in the width direction of the cell are equal in the th band region 11, and the position in the width direction of the cell 10 and the cell in the (n + 1) th band region 11 is Capacitance cells 21b are arranged at equal positions. The capacity cell 21a is connected to two power supply wires 12a and 12b that sandwich the capacity cell 21a. The capacity cell 21b is similar to this.

  In the semiconductor integrated circuit according to the present embodiment, in addition to the cell placement prohibited area set around the cells on the clock path, the capacity cells 21a and 21b are placed in the cell placement prohibited area. It is characterized by being. As shown in FIG. 10, both ends of the capacity cells 21a and 21b are connected to a power supply wiring 12a to which the power supply voltage VDD is applied and a power supply wiring 12b to which the ground voltage VSS is applied. Such capacity cells 21a and 21b have a function of stabilizing the power supplied via the power wirings 12a and 12b. Therefore, according to the semiconductor integrated circuit according to the present embodiment, the power supply supplied via the power supply wiring is stabilized by providing the capacitor cell in the cell placement prohibited area, so that the clock skew caused by IR-drop occurs. In addition, it is possible to more effectively prevent the malfunction of the circuit. When IR-drop is suppressed to the same extent in a semiconductor integrated circuit having a capacity cell and a semiconductor integrated circuit not having a capacity cell, the cell placement prohibition region can be made smaller in the semiconductor integrated circuit having the capacity cell. Therefore, the chip size can be reduced.

  In the above description, as an example of the semiconductor integrated circuit according to the present embodiment, the width A is set to W (the width of the cell 10) in the cell placement prohibition region 13 shown in FIG. ), A cell placement prohibition region having a width B of 0 is set. Alternatively, a cell placement prohibited area having a shape and size other than those described above may be set for the cell 10 on the clock path, or the cell group may be set for the cell group on the clock path. A cell placement prohibited area may be set for each. Similarly to the first embodiment, a cell placement prohibition region may be set for all cells (or cell groups) on the clock path, or cells (or cell groups) on the clock path. ) May be set for a part of the cell placement prohibited area.

  Next, a method for designing the semiconductor integrated circuit according to the present embodiment will be described. FIG. 11 is a flowchart showing a method for designing a semiconductor integrated circuit according to the present embodiment. The design method shown in FIG. 11 is typically executed using an EDA system, similarly to the design method described in the first embodiment.

  In the method shown in FIG. 11, first, a composite cell including each cell and a capacity cell is generated for a cell on the clock path included in the circuit to be designed (step S301). In step S301, a composite cell may be generated for all of the cells on the clock path, or a composite cell may be generated for a part of the cells on the clock path.

  For example, in the case where the cell placement prohibited area is set by the same method as in FIG. 2 for the cell 22 having the height H and the width W shown in FIG. When the width B is 0, in step S301, a composite cell 25b having a height (3H + 2h) and a width W shown in FIG. 12B is generated. The composite cell 25b includes a cell 22 and capacity cells 23a and 23b. Inside the composite cell 25b, the cell 22 and the capacity cells 23a and 23b are arranged in a line so that the positions in the cell width direction are equal. Arranged side by side. In the case where the cell placement prohibited area is set by the same method as in FIG. 2 for the delay cell group 24 composed of D delay cells having the height H and the width W shown in FIG. When (D + 2) W and width B are set to 0, in step S301, a composite cell 25d having an H-shaped shape shown in FIG. 12C is generated. The composite cell 25d includes a delay cell group 24 and capacity cells 23c and 23d. Within the composite cell 25d, the delay cell group 24 and the capacity cells 23c and 23d have the same position in the cell width direction. So that they are arranged in a line. The same applies to the case where a cell placement prohibition region having a shape other than the above is set for a cell (or cell group) on the clock path.

  Next, the composite cell generated in step S301 is placed (step S302). In step S301, the composite cells are arranged such that the cells included in the composite cell are arranged in a plurality of strip-like regions provided in parallel to each other with the cell heights aligned. As a result, a layout result in which cells and capacitor cells on the clock path are arranged is obtained.

  Next, among the cells included in the circuit to be designed, cells that are not arranged in step S302 are arranged (step S303). In step S303, no cell is placed in the area where the composite cell has already been placed. Therefore, in step S303, the non-arranged cells are arranged with the same height in a portion excluding the area where the composite cells are arranged in the plurality of band-like areas where the composite cells are arranged in step S302. In this way, according to the design method shown in FIG. 11, a cell that performs a logical operation is not disposed in the vicinity of a cell on the clock path, and a capacitor cell is disposed. The semiconductor integrated circuit according to the embodiment can be designed.

  In the design method shown in FIG. 11, cell placement prohibited areas are collectively set and capacity cells are placed for all or part of the cells on the clock path. Therefore, according to the design method shown in FIG. 11, the placement blockage is individually set for each of a large number of cells on the clock path, and the process of placing the capacity cell is not performed. It is possible to design the semiconductor integrated circuit according to this embodiment, in which a cell that performs a logic operation is not disposed in the vicinity of a cell on the path, and a capacitor cell is disposed.

(Third embodiment)
In the third embodiment of the present invention, a method for designing a semiconductor integrated circuit in which the occurrence of clock skew caused by IR-drop is suppressed will be described. FIG. 13 is a flowchart showing a method for designing a semiconductor integrated circuit according to the present embodiment. The design method shown in FIG. 13 is typically executed using an EDA system, similarly to the design methods described in the first and second embodiments.

  In the method shown in FIG. 13, first, all the cells included in the circuit to be designed are arranged (step S401). By executing step S401, for example, a layout result shown in FIG. 19 is obtained. Next, the IR-drop amount is obtained for the cells on the clock path among the cells included in the circuit to be designed (step S402). Here, the IR-drop amount is the amount of drop when the power supply voltage supplied to the cell drops due to the resistance of the power supply wiring when a predetermined power supply voltage is supplied from the outside of the semiconductor integrated circuit. Say. The IR-drop amount can be obtained based on the layout result of the semiconductor integrated circuit. In step S402, the IR-drop amount may be obtained for all the cells on the clock path, or the IR-drop amount may be obtained for a part of the cells on the clock path.

  Next, it is determined whether or not all the obtained IR-drop amounts are equal to or less than a predetermined allowable value (step S403). If it is determined in step S403 that all the obtained IR-drop amounts are equal to or less than the predetermined allowable value (YES in step S403), the process ends. In other cases (NO in step S403), the process proceeds to step S404. In this case, when the cell whose IR-drop amount exceeds the allowable value is Cx, the cell arranged closest to the cell Cx is rearranged at a position away from the cell Cx (step S404). Next, the process proceeds to step S402. Thereby, in step S403, until it is determined that all the obtained IR-drop amounts are equal to or less than the allowable value, three of the rearrangement of cells, calculation of the IR-drop amount, and determination on the IR-drop amount are performed. The steps are executed repeatedly.

  In step S404, when the IR-drop amount of the cell Cx exceeds the allowable value, the cell arranged closest to the cell Cx is rearranged at a position away from the cell Cx. Generally speaking, in the step of rearranging the cells, the cells arranged in the vicinity of the cell Cx may be rearranged at a position away from the cell Cx. For example, in the step of rearranging the cells, a cell that most affects the IR-drop amount of the cell Cx may be detected, and the cell may be rearranged at a position away from the cell Cx.

  With reference to FIG. 14, an example of execution of the semiconductor integrated circuit design method according to the present embodiment will be described. For example, assume that the layout result shown in FIG. 14A is obtained as a result of executing step S401 on the circuit to be designed. In FIG. 14A, cells 31, 32, and 33 are arbitrary types of cells on the clock path. Next, in step S402, the IR-drop amount is calculated for the cells 31, 32, and 33 on the clock path based on the circuit layout result. For example, if a power supply voltage of 3.0 V is supplied to the circuit, and the power supply voltages supplied to the cells 31, 32, and 33 are 2.9 V, 2.8 V, and 2.5 V, respectively, the cell The IR-drop amounts ΔV of 31, 32, and 33 are 0.1 V, 0.2 V, and 0.5 V, respectively (see FIG. 14B).

  Next, in step S403, it is determined whether the IR-drop amount of the cells 31, 32, 33 is equal to or less than a predetermined allowable value. For example, when the IR-drop amount allowable value is 0.3 V, it is determined that the IR-drop amount of the cell 33 exceeds the allowable value. Therefore, in step S404, the cell 36 arranged closest to the cell 33 is selected from the cells 34, 35, 36 arranged in the vicinity of the cell 33, and the cell 36 is selected as shown in FIG. As shown in FIG. In FIG. 14C, the position of the cell 36 before the rearrangement is indicated by a broken line, and the position of the cell 36 after the rearrangement is indicated by a solid line.

  As described above, in the method for designing a semiconductor integrated circuit according to this embodiment, when the IR-drop amount of a cell on the clock path exceeds the allowable value, the IR-drop amount is less than the allowable value. Until it is, the cells arranged in the vicinity of the cells on the clock path are rearranged at positions away from the cells on the clock path. Therefore, according to the design method of the present embodiment, it is possible to design a semiconductor integrated circuit in which the occurrence of clock skew due to IR-drop is suppressed without moving cells on the clock path.

(Fourth embodiment)
In the fourth embodiment of the present invention, a semiconductor integrated circuit in which generation of clock skew due to IR-drop is suppressed will be described. FIG. 15 is a diagram showing a layout result of the semiconductor integrated circuit according to the present embodiment. The semiconductor integrated circuit shown in FIG. 15 includes a plurality of cells (rectangular regions with a letter C) and wiring that connects the cells. In FIG. 15, for simplification of the drawing, only some cells are shown, and wirings other than the power supply wiring for connecting the cells are omitted.

  The cell shown in FIG. 15 is a standard cell, the cells are arranged in a plurality of strip-shaped regions 41 with the same height, and the two types of power supply wirings 42a in the two-dimensional region where the strip-shaped regions 41 are arranged. The point provided with 42b is the same as that of the semiconductor integrated circuit according to the first embodiment. The power supply wirings 42a and 42b are connected to power supply wirings 43a and 43b extending in the height direction of the cell via contacts (in FIG. 15, rectangles marked with x). A power supply voltage VDD is applied to the power supply wirings 42a and 43a, and a ground voltage VSS is applied to the power supply wirings 42b and 43b. In this way, the power supply voltage supplied from the outside of the semiconductor integrated circuit is supplied to each cell except the cell 40 via the power supply wirings 42a, 42b, 43a, 43b.

  In FIG. 15, a cell 40 is any type of cell on the clock path. As described in the first embodiment, the cells on the clock path are required to be less susceptible to IR-drop than the other cells. Therefore, the semiconductor integrated circuit according to the present embodiment is characterized by including a dedicated power supply wiring for supplying power to the cell 40.

  For this reason, the semiconductor integrated circuit according to the present embodiment includes clock dedicated power supply wirings 45a and 45b. The clock power supply wires 45 a and 45 b are wires extending in the height direction of the cell, and are provided in the vicinity of the cell 40. The power supply wirings 42a and 42b sandwiching the cell 40 are cut at four locations in the vicinity of the cell 40 (locations indicated by arrows in FIG. 15) in order to separate the cell 40 from the power supply wirings 42a and 42b. Thereby, relatively short power supply wirings 44 a and 44 b with both ends cut are formed in the vicinity of the cell 40. The cell 40 is connected to power supply wirings 44a and 44b, and the power supply wirings 44a and 44b are connected to clock dedicated power supply wirings 45a and 45b through contacts. In this manner, the power supply voltage supplied from the outside of the semiconductor integrated circuit is supplied to the cell 40 via the clock dedicated power supply wires 45a and 45b and the power supply wires 44a and 44b.

  In summary, the semiconductor integrated circuit according to the present embodiment supplies power to the first power supply wirings 44 a, 44 b, 45 a, 45 b that supply power to the cell 40 on the clock path and to cells other than the cell 40. Second power supply wirings 42a, 42b, 43a, 43b are provided. The first power supply wiring is a wiring provided separately from the second power supply wiring in order to supply power to the cell 40. For example, the first and second power supply wirings may be connected to separate power supply terminals, and these two types of power supply wirings may not be connected inside the semiconductor integrated circuit. Alternatively, the first and second power supply wirings may not be connected in the two-dimensional area where the cells are arranged, but may be connected outside the two-dimensional area where the cells are arranged.

  In the conventional semiconductor integrated circuit (FIG. 19), all the cells are supplied with power from the same power supply wiring. For this reason, when cells other than the cells on the clock path operate, a current flows through the power supply wiring, the power supply voltage supplied to the cells on the clock path drops, and clock skew occurs. When such a clock skew occurs, there is a possibility that the circuit malfunctions.

  In contrast, the semiconductor integrated circuit according to the present embodiment includes a dedicated power supply wiring for supplying power to the cells on the clock path, so that no other cell is connected to the power supply wiring. ing. Therefore, even when a cell other than the cells on the clock path operates, the influence does not reach the dedicated power supply wiring, so that the occurrence of clock skew due to IR-drop can be suppressed.

  In the above description, as an example, a dedicated power supply wiring is provided to supply power to the cells 40 on the clock path. However, on the clock path included in the semiconductor integrated circuit, there are usually many power supply wirings. Cells are included. Therefore, in a general semiconductor integrated circuit, instead of providing a dedicated power supply wiring for all the cells on the clock path, a dedicated power supply wiring is provided for a part of the cells on the clock path. .

  Further, in the case where the dedicated power supply wiring is provided after all the cells are arranged, if the cell is already arranged at a position where the dedicated power supply wiring is to be provided, for example, an ECO (Engineering Change Order) process ( The cells may be rearranged by the process of rearranging the arranged cells individually. For example, after the layout result shown in FIG. 16A is obtained, the clock dedicated power supply lines 47a and 47b are provided in the vicinity of the cell 46 on the clock path (in FIG. 16A, immediately to the right of the cell 46). When the cell 48 is provided, the cell 48 becomes an obstacle. In this case, as shown in FIG. 16B, the cells 48 may be rearranged at positions that do not interfere with the clock dedicated power supply wires 47a and 47b. In FIG. 16B, the position of the cell 48 before rearrangement is indicated by a broken line, and the position of the cell 48 after rearrangement is indicated by a solid line.

(Fifth embodiment)
In the fifth embodiment of the present invention, a semiconductor integrated circuit in which occurrence of clock skew due to IR-drop is suppressed will be described. FIG. 17 is a diagram showing a power supply method in the semiconductor integrated circuit according to the present embodiment. A semiconductor integrated circuit shown in FIG. 17 includes a plurality of cells (not shown), wiring (not shown) connecting the cells, a power supply terminal 51, power supply wiring 52 extending in a predetermined direction (vertical direction in FIG. 17), And the power supply wiring 53 extended in the direction (horizontal direction in FIG. 17) orthogonal to the power supply wiring 52 is provided. The power supply terminal 51 is connected to a power supply wiring 52, the power supply wiring 52 is connected to a power supply wiring 53 through a contact 54, and a cell (not shown) is connected to the power supply wiring 53. For example, a power supply voltage of 3.0 V is applied to the power supply terminal 51. As a result, a power supply voltage of 3.0 V is supplied to the cells included in the semiconductor integrated circuit.

  In addition to the above-described components, the semiconductor integrated circuit shown in FIG. 17 includes a power supply terminal 55, a reinforcing power supply wiring 56 extending in parallel with the power supply wiring 52, and a power transistor 57. The power supply terminal 55 is connected to the reinforcing power supply wiring 56, and the reinforcing power supply wiring 56 is connected to the power supply wiring 53 via the power transistor 57. A power supply voltage higher than the power supply voltage applied to the power supply terminal 51, for example, 5.0 V is applied to the power supply terminal 55.

  FIG. 18 is a diagram showing details of the power transistor 57. As shown in FIG. 18, the power transistor 57 has a source terminal, a gate terminal, and a drain terminal. The source terminal of the power transistor 57 is connected to the reinforcing power supply wiring 56, the gate terminal is grounded, and the drain terminal is connected to the power supply wiring 53. The power transistor 57 grounded in this way functions as a level shift circuit, and the power supply voltage of 5.0 V on the reinforcing power supply wiring 56 connected to the source terminal is reduced to a voltage of 3.0 V to be supplied to the cell. The voltage is lowered and applied to the power supply wiring 53 connected to the drain terminal.

  In the conventional semiconductor integrated circuit, as shown in FIG. 20, a large IR-drop occurs at the center of the chip. Therefore, in order to ensure that the circuit does not malfunction even when an IR-drop occurs, a method of designing a circuit after setting a design margin in consideration of the IR-drop is employed.

  In addition, a method (backing method) in which a power supply wiring is directly added to the center portion of the chip is also known in order to eliminate the influence of IR-drop generated at the center portion of the chip. However, even if the backing method is used, since the added power supply wiring also includes a resistance component, the power supply voltage supplied to each cell via the added power supply wiring also drops. Therefore, if the power supply voltage at the same level as that of the original power supply wiring is applied to the added power supply wiring, the effect of suppressing the IR-drop generated in the central portion of the chip is limited.

  On the other hand, in the semiconductor integrated circuit according to the present embodiment, a power supply voltage at a higher level than the original power supply wiring is applied to the added power supply wiring, and the power supply voltage applied to the added power supply wiring is By the action of the transistor, it is lowered to the power supply voltage to be supplied to the cell. Therefore, according to the semiconductor integrated circuit according to the present embodiment, it is possible to effectively suppress the IR-drop generated at the center portion of the chip and to suppress the occurrence of clock skew due to the IR-drop.

  In the above description, the semiconductor integrated circuit includes one power supply terminal 55, one reinforcing power supply wiring 56, and one power transistor. However, the semiconductor integrated circuit may include a plurality of these components.

  The semiconductor integrated circuit and the design method thereof according to the present invention have an effect of preventing the occurrence of clock skew caused by IR-drop. Therefore, the semiconductor integrated circuit designed by the cell base method, and some circuits are cell based. The present invention can be used for various semiconductor integrated circuits such as a semiconductor integrated circuit designed by the method.

The figure which shows the layout result of the semiconductor integrated circuit which concerns on the 1st Embodiment of this invention The figure which shows the cell arrangement | positioning prohibition area | region in the semiconductor integrated circuit which concerns on the 1st Embodiment of this invention. The figure which shows the other layout result in the semiconductor integrated circuit which concerns on the 1st Embodiment of this invention 1 is a diagram showing a delay cell group included in a semiconductor integrated circuit according to a first embodiment of the present invention. The figure which shows the other layout result in the semiconductor integrated circuit which concerns on the 1st Embodiment of this invention 1 is a flowchart showing a first design method of a semiconductor integrated circuit according to the first embodiment of the present invention; The figure which shows the dummy cell used with the 1st design method of the semiconductor integrated circuit which concerns on the 1st Embodiment of this invention The figure which shows the other dummy cell used with the 1st design method of the semiconductor integrated circuit concerning the 1st Embodiment of this invention 6 is a flowchart showing a second design method of the semiconductor integrated circuit according to the first embodiment of the present invention. The figure which shows the layout result of the semiconductor integrated circuit which concerns on the 2nd Embodiment of this invention 7 is a flowchart showing a method for designing a semiconductor integrated circuit according to the second embodiment of the present invention. The figure which shows the composite cell used with the design method of the semiconductor integrated circuit which concerns on the 2nd Embodiment of this invention. 7 is a flowchart showing a method for designing a semiconductor integrated circuit according to the third embodiment of the present invention. The figure which shows the execution example of the design method of the semiconductor integrated circuit which concerns on the 3rd Embodiment of this invention The figure which shows the layout result of the semiconductor integrated circuit which concerns on the 4th Embodiment of this invention The figure which shows a mode that a cell is rearranged in order to obtain the semiconductor integrated circuit which concerns on the 4th Embodiment of this invention. Schematic diagram showing a power supply method in a semiconductor integrated circuit according to a fifth embodiment of the present invention The figure which shows the power transistor contained in the semiconductor integrated circuit which concerns on the 5th Embodiment of this invention The figure which shows the layout result of the conventional semiconductor integrated circuit The figure which shows a mode that IR-drop generate | occur | produces in the conventional semiconductor integrated circuit.

Explanation of symbols

10, 15, 22, 31 to 36, 40, 46, 48... Cell 11, 41... Strip-like region 12, 42 to 44, 52, 53. 16, 18 ... dummy cells 21, 23 ... capacity cells 25 ... composite cells 45, 47 ... clock power supply wires 51, 55 ... power supply terminals 54 ... contacts 56 ... reinforcing power supply wires 57 ... power transistors 91 ... strip regions 92, 95 ... Power supply wiring 93 ... Semiconductor integrated circuit 94 ... Power supply terminal 96 ... Resistance component 97 ... Cell

Claims (3)

A semiconductor integrated circuit designed in a cell-based manner,
A plurality of cells arranged in a two-dimensional region;
A power supply line provided in an upper wiring layer in the two-dimensional region and supplying power to the cell via a contact via;
Reinforcing power supply wiring provided separately from the power supply wiring in the upper wiring layer in the two-dimensional region, and applied with a voltage higher than the power supply wiring;
A semiconductor integrated circuit, comprising: a voltage conversion unit that is provided in the two-dimensional region and drops the voltage on the reinforcing power supply wiring to a power supply voltage to be supplied to the cell, and applies the voltage to the power supply wiring.   The semiconductor integrated circuit according to claim 1, wherein the voltage conversion unit includes a power transistor.   2. The semiconductor integrated circuit according to claim 1, wherein the power supply wiring and the reinforcing power supply wiring are arranged in the same wiring layer.

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