Method and system for modeling variation of circuit parameters in delay calculation for timing analysis

• US 7,310,792 B2
• Filed: 12/15/2004
• Issued: 12/18/2007
• Est. Priority Date: 06/15/2004
• Status: Expired due to Fees

• Current Assignee: Cadence Design Systems Incorporated (Cadence Group)
• Original Assignee: Cadence Design Systems Incorporated (Cadence Group)
• Inventors: Verghese, Nishath K., Zhao, Hong
• Primary Examiner(s): Siek, Vuthe
• Application Number:
  US11/014,096
• Publication Number:
  US 20050278671A1
• Time in Patent Office: 1,098 Days
• Field of Search: 716 5- 6, 716/1, 716/4, 703/2
• US Class Current: 716/113
• CPC Class Codes: G06F 30/3312 Timing analysis

Abstract

A system, method, and computer program accurately models circuit parameter variation for delay calculation. For any given circuit parameter value, a cell is characterized at just three values in the circuit parameter range. An interpolation process generates an equation to calculate delay using the characterization data from the three circuit parameter values. This delay equation calculates the delay for any value in the circuit parameter range. Similar methodology is used to model simultaneous variation of two circuit parameters. The cell is characterized at just six circuit parameter pairs to interpolate the delay equation for any circuit parameter pair in the characterized ranges. This methodology can be extended to accommodate variation of multiple circuit parameters using similar interpolation techniques.

Claims

1. A computerized method for modeling variations in circuit parameters in delay calculations for timing analysis of circuit designs comprising:

characterizing the circuit design at each of the set of predetermined circuit parameter values, each of the parameter values being within a range, the characterization results for each parameter value being stored on computer readable medium;

deriving an equation for calculating an output waveform of the circuit design based on the stored circuit characterization results;

calculating the output waveform to extract a delay at a given input parameter value using the derived equation, the given input parameter value being any value within the range; and

storing a value of the delay in a computer readable tangible medium for use in electronic design automation.

2. The method of claim 1, where the predetermined circuit parameter values and the given input parameter value can be any one of supply voltage, temperature, and process, process representing a collection of parameters including oxide thickness, threshold voltage, transistor width, and transistor length.

3. The method of claim 2, wherein the set of predetermined parameter values comprises no more than three values.

4. The method of claim 2, wherein deriving the equation comprises:

inputting a slew, a load capacitance, and the given input parameter value;

obtaining a driving current value from the characterization results of each parameter value in the set of predetermined parameters based on the slew and load capacitance;

forming an equation for each of the obtained driving current values; and

solving for a set of unknown coefficients in the formed equations.

5. The method of claim 4, wherein the predetermined circuit parameter values and the given input parameter value are supply voltage.

6. The method if claim 4, wherein the equation is

$i_d={\frac{\beta }{}}^{}$

2 ⁡

[ V - V th ⁢

⁢

0 ] q ,

where i_d is the obtained driving current, and β

, V_tho, and q are the unknown coefficients.

7. The method of claim 6, wherein calculating the waveform and the delay at a given input parameter value using the derived equation, comprises

entering the given input parameter supply voltage, V, into the equation;

entering the solved coefficients into the equation; and

solving the equation.

8. The method of claim 1, wherein the characterization results for each parameter value comprise the delay value and a plurality of points forming the output waveform.

9. The method of claim 1 wherein the set of predetermined parameter values comprises no more than six value pairs, each value pair comprising one each of any two of supply voltage, temperature, and process, process representing a collection of parameters including oxide thickness, threshold voltage, transistor width and transistor length.

10. The method of claim 9, wherein deriving the equation comprises:

inputting a slew, a load capacitance, and the two given input parameter values;

obtaining a driving current value from the characterization results of each parameter value in the set of predetermined parameters based on the slew and load capacitance;

forming an equation for each of the obtained driving current values; and

solving for a set of unknown coefficients in the formed equations.

11. The method of claim 10, wherein the value pair is comprised of supply voltage and temperature.

12. The method of claim 11, wherein the equation is

$i_d=\frac{\beta }{}$

2 ⁢

( T Tnom ) P ⁡

[ V - Vtho - δ

⁡

( T - Tnom ) ] q ,

where i_d is the obtained driving current, and β

, V_tho, q, P, Tnom, and δ

are the unknown coefficients.

13. The method of claim 12, wherein calculating the waveform and the delay at a given input parameter value using the derived equation, comprises:

entering the given input parameter supply voltage, V, and given input parameter temperature, T, into the equation;

entering the solved coefficients into the equation; and

solving the equation based on the given input parameters.

14. A circuit design formed by the method of claim 1.

15. A computerized method for modeling variations in circuit parameters in delay calculations for timing analysis of circuit designs comprising:

characterizing the circuit design at each of the set of predetermined circuit parameter values, each of the parameter values being within a range, the characterization results for each parameter value being stored on computer readable medium;

deriving an equation for calculating an output waveform of the circuit design based on the stored circuit characterization results;

modeling the output waveform to extract a delay at a given input parameter value using the derived equation, the input parameter value being any value within the range; and

storing a value of the delay in a computer readable tangible medium for use in electronic design automation.

16. A computer program product embodied on computer readable medium, the computer readable medium having stored thereon a sequence of instructions which, when executed by a processor, causes the processor to execute a method for modeling variations in circuit parameters in delay calculations for timing analysis of circuit designs, the method comprising:

characterizing the circuit design at each of the set of predetermined circuit parameter values, each of the parameter values being within a range, the characterization results for each parameter value being stored on computer readable medium;

deriving an equation for calculating an output waveform of the circuit design based on the stored circuit characterization results;

calculating the output waveform to extract a delay at a given input parameter value using the derived equation, the given input parameter value being any value within the range; and

storing a value of the delay in a computer readable tangible medium for use in electronic design automation.

17. The computer program of claim 16, where the predetermined circuit parameter values and the given input parameter value can be any one of supply voltage, temperature, and process, process representing a collection of parameters including oxide thickness, threshold voltage, transistor width, and transistor length.

18. The computer program of claim 17, wherein the set of predetermined parameter values comprises no more than three values.

19. The computer program of claim 17, wherein deriving the equation comprises:

inputting a slew, a load capacitance, and the given input parameter value;

obtaining a driving current value from the characterization results of each parameter value in the set of predetermined parameters based on the slew and load capacitance;

forming an equation for each of the obtained driving current values; and

solving for a set of unknown coefficients in the formed equations.

20. The computer program of claim 19, wherein the predetermined circuit parameter values and the given input parameter value are supply voltage.

21. The computer program if claim 20, wherein the equation is

$i_d={\frac{\beta }{}}^{}$

2 ⁡

[ V - V th ⁢

⁢

0 ] q ,

where i_d is the obtained driving current, and β

, V_tho, and q are the unknown coefficients.

22. The computer program of claim 21, wherein calculating the waveform and the delay at a given input parameter value using the derived equation, comprises:

entering the given input parameter supply voltage, V, into the equation;

entering the solved coefficients into the equation; and

solving the equation.

23. The computer program of claim 16, wherein the characterization results for each parameter value comprise the delay value and a plurality of points forming the output waveform.

24. The computer program of claim 16, wherein the set of predetermined parameter values comprises no more than six value pairs, each value pair comprising one each of any two of supply voltage, temperature, and process, process representing a collection of parameters including oxide thickness, threshold voltage, transistor width and transistor length.

25. The computer program of claim 24, wherein deriving the equation comprises:

inputting a slew, a load capacitance, and the two given input parameter values;

obtaining a driving current value from the characterization results of each parameter value in the set of predetermined parameters based on the slew and load capacitance;

forming an equation for each of the obtained driving current values; and

solving for a set of unknown coefficients in the formed equations.

26. The computer program of claim 25, wherein the value pair is comprised of supply voltage and temperature.

27. The computer program of claim 26, wherein the equation is

$i_d=\frac{\beta }{}$

2 ⁢

( T Tnom ) P ⁡

[ V - Vtho - δ

⁡

( T - Tnom ) ] q ,

where i_d is the obtained driving current, and β

, V_tho, q, P, Tnom, and δ

are the unknown coefficients.

28. The computer program of claim 27, wherein calculating the waveform and the delay at a given input parameter value using the derived equation, comprises:

entering the given input parameter supply voltage, V, and given input parameter temperature, T, into the equation;

entering the solved coefficients into the equation; and

solving the equation based on the given input parameters.

29. A system for modeling variations in circuit parameters in delay calculations for timing analysis of circuit designs comprising:

logic for characterizing the circuit design at each of the set of predetermined circuit parameter values, each of the parameter values being within a range, the characterization results for each parameter value being stored on computer readable medium;

logic for deriving an equation for calculating an output waveform of the circuit design based on the stored circuit characterization results;

logic for calculating the output waveform to extract a delay at a given input parameter value using the derived equation, the given input parameter value being any value within the range; and

logic for storing a value of the delay in a computer readable tangible medium for use in electronic design automation.

30. The system of claim 29, where the predetermined circuit parameter values and the given input parameter value can be any one of supply voltage, temperature, and process, process representing a collection of parameters including oxide thickness, threshold voltage, transistor width, and transistor length.

31. The system of claim 29, wherein the set of predetermined parameter values comprises no more than three values.

32. The system of claim 30, wherein logic for deriving the equation comprises:

logic for inputting a slew, a load capacitance, and the given input parameter value;

logic for obtaining a driving current value from the characterization results of each parameter value in the set of predetermined parameters based on the slew and load capacitance;

logic for forming an equation for each of the obtained driving current values; and

logic for solving for a set of unknown coefficients in the formed equations.

33. The system of claim 32, wherein the predetermined circuit parameter values and the given input parameter value are supply voltage.

34. The system if claim 33, wherein the equation is

$i_d={\frac{\beta }{}}^{}$

2 ⁡

[ V - V th ⁢

⁢

0 ] q ,

where i_d is the obtained driving current, and β

, V_tho, and q are the unknown coefficients.

35. The system of claim 34, wherein logic for calculating the waveform and the delay at a given input parameter value using the derived equation, comprises:

logic for entering the given input parameter supply voltage, V, into the equation;

logic for entering the solved coefficients into the equation; and

logic for solving the equation.

36. The system of claim 29, wherein the characterization results for each parameter value comprise the delay value and a plurality of points forming the output waveform.

37. The system of claim 29 wherein the set of predetermined parameter values comprises no more than six value pairs, each value pair comprising one each of any two of supply voltage, temperature, and process, process representing a collection of parameters including oxide thickness, threshold voltage, transistor width and transistor length.

38. The system of claim 37, wherein logic for deriving the equation comprises:

logic for inputting a slew, a load capacitance, and the two given input parameter values;

logic for obtaining a driving current value from the characterization results of each parameter value in the set of predetermined parameters based on the slew and load capacitance;

logic for forming an equation for each of the obtained driving current values; and

logic for solving for a set of unknown coefficients in the formed equations.

39. The system of claim 38, wherein the value pair is comprised of supply voltage and temperature.

40. The system of claim 39, wherein the equation is

$i_d=\frac{\beta }{}$

2 ⁢

( T Tnom ) P ⁡

[ V - Vtho - δ

⁡

( T - Tnom ) ] q ,

where i_d is the obtained driving current, and β

, V_tho, q, P, Tnom, and δ

are the unknown coefficients.

41. The system of claim 40, wherein logic for calculating the waveform and the delay at a given input parameter value using the derived equation, comprises:

logic for entering the given input parameter supply voltage, V, and given input parameter temperature, T, into the equation;

logic for entering the solved coefficients into the equation; and

logic for solving the equation based on the given input parameters.