Logic synthesis method, semiconductor integrated circuit and arithmetic circuit
First Claim
1. A method for designing a semiconductor integrated circuit having a plurality of combinational circuits each of which includes a signal propagation path and having registers which are provided at stages respectively preceding and succeeding at least one of said plurality of combinational circuits, said method comprising:
- a first step of mapping, when there exists a combinational circuit in said plural combinational circuits of which signal propagation path has a signal propagation delay not more than a design delay upper limit, said combinational circuit into a combinational circuit of a first type driven by a low voltage from a low-voltage source, and mapping, when there exists a combinational circuit in said plural combinational circuits of which signal propagation path has a signal propagation delay above the design delay upper limit, said combinational circuit into a combinational circuit of a second type of which part is driven by a high voltage from a high-voltage source and of which remaining part is driven by a low voltage from said low-voltage source in order that the signal propagation path of said combinational circuit has a signal propagation delay below the design delay upper limit; and
a second step of remapping, when there is found as a result of checking, a mixture in which an output from said remaining part of said second-type combinational circuit that is driven by a low voltage from said low-voltage source is input to a part of another second-type combinational circuit that is driven by a high voltage from said high-voltage source, said remaining part of said second-type combinational circuit that is driven by a low voltage from said low-voltage source so as to be driven by a high voltage from said high-voltage source.
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Abstract
A top-down design technique is used to design a semiconductor integrated circuit having a plurality of registers and a plurality of combinational circuits each of which is connected between the registers. When a semiconductor integrated circuit is logic-synthesized from a register transistor level, a front section of a critical path-containing combinational circuit is driven by a high voltage from a high-voltage source while the remaining section and other combinational circuits with no critical path are driven by a low voltage from a low-voltage source. A level shifter is placed at the stage before the critical path-containing combinational circuit. The level shifter converts a low-voltage signal into a high-voltage one. This invention facilitates logic synthesis of a low-power semiconductor circuit without increasing the maximum signal propagation delay of the critical path and without having to provide a level shifter in a combinational circuit.
50 Citations
32 Claims
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1. A method for designing a semiconductor integrated circuit having a plurality of combinational circuits each of which includes a signal propagation path and having registers which are provided at stages respectively preceding and succeeding at least one of said plurality of combinational circuits, said method comprising:
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a first step of mapping, when there exists a combinational circuit in said plural combinational circuits of which signal propagation path has a signal propagation delay not more than a design delay upper limit, said combinational circuit into a combinational circuit of a first type driven by a low voltage from a low-voltage source, and mapping, when there exists a combinational circuit in said plural combinational circuits of which signal propagation path has a signal propagation delay above the design delay upper limit, said combinational circuit into a combinational circuit of a second type of which part is driven by a high voltage from a high-voltage source and of which remaining part is driven by a low voltage from said low-voltage source in order that the signal propagation path of said combinational circuit has a signal propagation delay below the design delay upper limit; and a second step of remapping, when there is found as a result of checking, a mixture in which an output from said remaining part of said second-type combinational circuit that is driven by a low voltage from said low-voltage source is input to a part of another second-type combinational circuit that is driven by a high voltage from said high-voltage source, said remaining part of said second-type combinational circuit that is driven by a low voltage from said low-voltage source so as to be driven by a high voltage from said high-voltage source. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21)
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22. A method for designing a semiconductor integrated circuit having a plurality of combinational circuits each of which includes a signal propagation path and having registers which are provided at stages respectively preceding and succeeding at least one of said plurality of combinational circuits, said method comprising:
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a first step of mapping, when there exists a combinational circuit in said plural combinational circuits of which signal propagation path has a signal propagation delay not more than a design delay upper limit, said combinational circuit into a combinational circuit of a first type driven by a low voltage from a low-voltage source; a second step of mapping, when there exists a combinational circuit in said plural combinational circuits of which signal propagation path has a signal propagation delay above the design delay upper limit, said combinational circuit into a combinational circuit of a second type driven by a high voltage from a high-voltage source; and a third step of mapping each said register into a register driven by a low voltage from said low-voltage source; wherein the difference in electric potential between a high voltage from said high-voltage source and a low voltage from said low-voltage source is held at a value below the threshold voltage of transistors forming said combinational circuits and registers. - View Dependent Claims (23, 24, 25)
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26. A method for designing a semiconductor integrated circuit having a plurality of combinational circuits each of which includes a signal propagation path and having registers which are provided at stages respectively preceding and succeeding at least one of said plurality of combinational circuits, said method comprising:
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a first step of mapping, when there exists a combinational circuit in said plural combinational circuits of which signal propagation path has a signal propagation delay not more than a design delay upper limit, said combinational circuit into a combination circuit of a first type driven by a low voltage from a low-voltage source; and a second step of mapping, when there exists a combinational circuit in said plural combinational circuits of which signal propagation path has a signal propagation delay above the design delay upper limit, said combinational circuit into a combinational circuit of a second type of which part is driven by a high voltage from a high-voltage source and of which remaining part of said combinational circuit is driven by a low voltage from said low-voltage source in order that the signal propagation path of said combinational circuit has a signal propagation delay below the design delay upper limit; wherein said second step further includes; (i) setting a plurality of windows each having a specified size and serving as a search range in a combinational circuit of which signal propagation path has a signal propagation delay above the design delay upper limit, said combinational-circuit-elements; and (ii) selecting from among said plural windows a window that contains a group of combinational-circuit-elements of said elements whose total area or total delay is the smallest, and mapping said combinational-circuit-elements of said group into said part of said second-type combinational circuit. - View Dependent Claims (27)
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28. A semiconductor integrated circuit having a plurality of combinational circuits each of which includes a signal propagation path and having registers which are provided at stages respectively preceding and succeeding at least one of said plurality of combinational circuits,
wherein: -
(i) said plural combinational circuits are formed by combinational circuits of a first type driven by a low voltage from a low-voltage source and combinational circuits of a second type driven by a high voltage from a high-voltage source; (ii) each of said plural registers is formed by a register driven by a low voltage from said low-voltage source; and (iii) the difference in electric potential between a high voltage from said high-voltage source and a low voltage from said low-voltage source is held at a value below the threshold voltage of transistors forming said combinational circuits and registers. - View Dependent Claims (29, 30, 31, 32)
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Specification