Method of estimating logic cell delay time
First Claim
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1. A method of determinig a delay time for a signal through a logic cell having at least one input pin and at least one output pin, comprising:
- (1) providing input data characteristic of the logic cell, said data including cell type, total capacitive load at said at least one input pin, total capacitive load at said at leas one output pin, and slew rate of a simulated signal applied to said at least on input pin, (2) providing a database of predetermined library ell data including base delay computation facts and sensitivity factors for a range of library cell types, (3) determinig from said input data and from said predetermined library cell data at least one edge delay base factor which approximates the delay time of an associated edge of a signal through the logic cell, said associated edge associated with a corresponding edge of said simulated signal, the delay time selected from at least one of a rising edge delay time associated with the rising edge of the signal and a falling edge delay time associated with the falling edge of the signal (4) determining a correction factor based substantially on the slew rate of the corresponding edge of said stimulated signal, and (5) adding said correction factor to said base delay factor to emulate delay time through the cell.
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Abstract
A method for approximating the delay time of an excitation through a logic cell using the summation of a base delay, which is a function of delay coefficients for the cell and the total output load capacitance of the cell, and a rise/fall time correction, which is determined from the output rise/fall time of the driving cell and the sensitivity of the analyzed cell to rise/fall time. Other corrections/compensating factors include a performance derating factor which accounts for the multiplicative effects of operating voltage, temperature and process.
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Citations
24 Claims
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1. A method of determinig a delay time for a signal through a logic cell having at least one input pin and at least one output pin, comprising:
- (1) providing input data characteristic of the logic cell, said data including cell type, total capacitive load at said at least one input pin, total capacitive load at said at leas one output pin, and slew rate of a simulated signal applied to said at least on input pin, (2) providing a database of predetermined library ell data including base delay computation facts and sensitivity factors for a range of library cell types, (3) determinig from said input data and from said predetermined library cell data at least one edge delay base factor which approximates the delay time of an associated edge of a signal through the logic cell, said associated edge associated with a corresponding edge of said simulated signal, the delay time selected from at least one of a rising edge delay time associated with the rising edge of the signal and a falling edge delay time associated with the falling edge of the signal (4) determining a correction factor based substantially on the slew rate of the corresponding edge of said stimulated signal, and (5) adding said correction factor to said base delay factor to emulate delay time through the cell.
- View Dependent Claims (2, 3, 4, 5, 6, 7)
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8. A method of determining a delay time of a signal through a logic cell which interfaces with one or more other logic cells, said logic cell having at least one input pin and at least one output pin, the method comprising the steps of:
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providing input data characteristic of the logic cell, said data including cell type, total capacitive load at said at least one input pin, total capacitive load at said at least one output pin, and slew rate of a simulated signal applied to said at least one input pin; providing a database of predetermined library cell data including base delay computation factors and sensitivity factors for a range of library cell types; determining from said library cell data and said input data at least on edge delay base factor which approximates the delay time of the associated edge of a signal through the logic cell, said associated edge associated with a corresponding edge of said simulated signal, the delay time being selected from at least one of a rising edge time associated with the rising edge of the signal and a falling edge delay time associated with the falling edge of the signal and wherein the respective edge delay times are obtained for the associated edges of the signal; calculating an edge delay correction factor based substantially upon the slew rate of the corresponding edge of said simulated signal applied to at least one input pin of said cell and upon the capacitance load at said at least one output pin; and adding the edge delay base factor to the corresponding edge delay correction factor to determine the delay time. - View Dependent Claims (9, 10, 11, 12, 13, 14)
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15. A method of determining delay time of a signal through a logic cell which interfaces with one or more other logic cells, said logic cell having at least one input pin and at least one output pin and at least one delay path, the method comprising the steps of:
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providing input data characteristic of the logic cell, said data including cell type, total capacitive load at said at least one input pin, total capacitive load at said at least one output pin, and slew rate of a simulated signal applied to said at least one input pin; providing a database of predetermined library cell data including base delay computation factors and sensitivity factors for a range of library cell types; determinig from said library cell data and said input data an edge delay base factor which approximates the delay time of the associated edge of signal through the logic cell, said associated edge associated with a corresponding edge of said impulse signal, the delay time being selected from a t least one of a rising edge delay time associated with a rising edge of the signal and a falling edge delay time associated with a falling edge of the signal and wherein the respective edge times are obtained for the associated edges of the signal; calculating an edge delay correction factor based substantially upon the slew rate of the corresponding edge of said simulated signal applied to at least one input pin of said cell, upon the capacitance load at said at least one output pin, and upon the delay path traversed by said signal; and adding the edge delay base factor tot he corresponding edge delay correction factors, to determine the delay time. - View Dependent Claims (16, 17, 18, 19, 20, 21)
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22. In the process of designing and fabricating an integrated circuit using a cell library, the steps of:
- determining an initial cell design;
emulating a delay time for the initial cell design;
further developing the cell design; and
, prior to fabricating an integrated circuit containing the cell, emulating a delay time for the developed cell, each emulation step comprising determining an edge delay base factor which approximates the delay time of at least one of the rising edge and the falling edge of a signal through the logic cell;
calculating an edge delay correction factor based substantially upon the slew rate of the signal applied to at least one input pin of the cell; and
adding the edge delay base factor to the corresponding edge delay correction factor to emulate the delay time. - View Dependent Claims (23, 24)
- determining an initial cell design;
Specification