Granted Patent B2

US 7,966,592 · App. 12/206,048 · Granted Jun 21, 2011

Abstract

Claims (51)

1. A method to analyze timing in a circuit, comprising the steps of:

(A) simulating a reception of both an input signal and a clock signal at a first flip-flop, wherein (i) said input signal has a latest transition, (ii) said input signal arrives through a first path of said circuit and (iii) said clock signal has an active edge;

(B) calculating, using a processor, a first value of a time difference between said latest transition and said active edge;

(C) calculating a first delay between said active edge and said latest transition appearing in an output signal of said first flip-flop, wherein (i) said first delay is based on a model responding to said first value, (ii) said model characterizes a clock-to-output delay of said first flip-flop as a function of said time difference and (iii) said characterization covering a range of values;

(D) calculating a first arrival time of said latest transition in said output signal at a second flip-flop, wherein said second flip-flop is connected to said first flip-flop through a second signal path; and

(E) storing said first arrival time in a recording medium.

2. The method according to claim 1 , wherein said range covers (i) from approximately a short value at which said first flip-flop cannot capture said latest transition (ii) to a long value at which said clock-to-output delay is approximately a minimum delay through said first flip-flop.

3. The method according to claim 1 , further comprising the step of:

conducting a static timing analysis of said circuit, wherein said static timing analysis does not indicate a circuit failure where (i) said first value of said time difference fails a first setup time of said first flip-flop and (ii) said first arrival time of said latest transition in said output signal meets a second setup time of said second flip-flop.

4. The method according to claim 3 , wherein said first setup time comprises a particular value of said time difference at which said clock-to-output delay is approximately a given percentage longer than a minimum clock-to-output delay of said first flip-flop.

5. The method according to claim 1 , further comprising the step of:

conducting a static timing analysis of said circuit, wherein said static timing analysis does not indicate a circuit failure where (i) said first value of said latest transition is too short to be captured by said first flip-flop and (ii) said first arrival time of said latest transition in said output signal meets a specified arrival time at said second flip-flop.

6. The method according to claim 1 , further comprising the step of:

conducting a static timing analysis of said circuit, wherein said static timing analysis analyzes said first path before said second path.

7. The method according to claim 1 , wherein said input signal further has an earliest transition, the method further comprising the steps of:

calculating a second value of said time difference between said earliest transition and said active edge;

calculating a second delay between said active edge and said earliest transition appearing in said output signal, wherein said second delay is based on said model responding to said second value;

calculating an second arrival time of said earliest transition in said output signal at said second flip-flop; and

storing said second arrival time in said recording medium.

8. The method according to claim 7 , wherein (i) said first path is dependent upon both a third path and a fourth path, (ii) said third path determines said latest transition and (iii) said fourth path determines said earliest transition.

9. A method to analyze timing in a circuit, comprising the steps of:

(A) simulating a reception of both an input signal and a clock signal at a first flip-flop, wherein (i) said input signal has an earliest transition, (ii) said input signal arrives through a first path of said circuit and (iii) said clock signal has an active edge;

(B) calculating, using a processor, a value of a time difference between said earliest transition and said active edge;

(C) calculating a delay between said active edge and said earliest transition appearing in an output signal of said first flip-flop, wherein (i) said delay is based on a model responding to said value, (ii) said model characterizes a clock-to-output delay of said first flip-flop as a function of said time difference and (iii) said characterization covering a range of values;

(D) calculating a first arrival time of said earliest transition in said output signal at a second flip-flop, wherein said second flip-flop is connected to said first flip-flop through a second signal path; and

(E) storing said first arrival time in a recording medium.

10. The method according to claim 9 , wherein said range covers (i) from approximately a short value at which said first flip-flop cannot capture said earliest transition (ii) to a long value at which said clock-to-output delay is approximately a minimum delay through said first flip-flop.

11. The method according to claim 9 , further comprising the step of:

conducting a static timing analysis of said circuit, wherein said static timing analysis does not indicate a circuit failure where (i) said value of said time difference fails a hold time of said first flip-flop and (ii) a second arrival time of a latest transition in said output signal meets a setup time of said second flip-flop.

12. The method according to claim 11 , wherein said hold time comprises a particular value of said time difference at which said clock-to-output delay is approximately a given percentage longer than a minimum clock-to-output delay of said first flip-flop.

13. The method according to claim 9 , further comprising the step of:

conducting a static timing analysis of said circuit, wherein said static timing analysis does not indicate a circuit failure where (i) said value of said earliest transition is too short to be captured by said first flip-flop and (ii) said first arrival time of said earliest transition in said output signal meets a specified arrival time at said second flip-flop.

14. The method according to claim 9 , further comprising the step of:

conducting a static timing analysis of said circuit, wherein said static timing analysis analyzes said first path before said second path.

15. A non-transitory storage medium for use in a computer to analyze timing in a circuit, the storage medium recording a computer program that is readable and executable by the computer, when executed the computer program comprising the steps of:

(A) simulating a reception of both an input signal and a clock signal at a first flip-flop, wherein (i) said input signal has a latest transition, (ii) said input signal arrives through a first path of said circuit and (iii) said clock signal has an active edge;

(B) calculating a first value of a time difference between said latest transition and said active edge;

(C) calculating a first delay between said active edge and said latest transition appearing in an output signal of said first flip-flop, wherein (i) said first delay is based on a model responding to said first value, (ii) said model characterizes a clock-to-output delay of said first flip-flop as a function of said time difference and (iii) said characterization covering a range of values;

(D) calculating a first arrival time of said latest transition in said output signal at a second flip-flop, wherein said second flip-flop is connected to said first flip-flop through a second signal path; and

(E) storing said first arrival time in a recording medium.

16. The storage medium according to claim 15 , wherein said range covers (i) from approximately a short value at which said first flip-flop cannot capture said latest transition (ii) to a long value at which said clock-to-output delay is approximately a minimum delay through said first flip-flop.

17. The storage medium according to claim 15 , wherein said computer program further comprises the step of:

conducting a static timing analysis on said circuit, wherein said static timing analysis does not indicate a circuit failure where (i) said first value of said time difference fails a first setup time of said first flip-flop and (ii) said first arrival time of said latest transition in said output signal meets a second setup time of said second flip-flop.

18. The storage medium according to claim 17 , wherein said first setup time comprises a particular value of said time difference at which said clock-to-output delay is approximately a given percentage longer than a minimum clock-to-output delay of said first flip-flop.

19. The storage medium according to claim 15 , wherein said computer program further comprises the step of:

conducting a static timing analysis on said circuit, wherein said static timing analysis does not indicate a circuit failure where (i) said first value of said latest transition is too short to be captured by said first flip-flop and (ii) said first arrival time of said latest transition in said output signal meets a specified arrival time at said second flip-flop.

20. The storage medium according to claim 15 , wherein said input signal further has an earliest transition, the computer program further comprising the steps of:

calculating a second value of said time difference between said earliest transition and said active edge;

calculating a second delay between said active edge and said earliest transition appearing in said output signal, wherein said second delay is based on said model responding to said second value;

calculating an second arrival time of said earliest transition in said output signal at said second flip-flop; and

storing said second arrival time in said recording medium.

Assignments (9)