Synthesizing current source driver model for analysis of cell characteristics

• US 7,761,275 B2
• Filed: 12/19/2005
• Issued: 07/20/2010
• Est. Priority Date: 12/19/2005
• Status: Expired due to Fees

• Current Assignee: International Business Machines Corporation
• Original Assignee: International Business Machines Corporation
• Inventors: Su, Haihua, Chopra, Kaviraj S., Kashyap, Chandramouli V.
• Primary Examiner(s): PROCTOR, JASON SCOTT
• Application Number:
  US11/311,038
• Publication Number:
  US 20070143719A1
• Time in Patent Office: 1,674 Days
• Field of Search: 703 13- 15, 716/1, 716 4- 6
• US Class Current: 703/14
• CPC Class Codes: G06F 30/30 Circuit design
• CPC Class Codes: G06F 30/367 Design verification, e.g. using simulation, simulation program with integrated circuit emphasis [SPICE], direct methods or relaxation methods

Abstract

A method for performing an analysis of at least one logic stage in a netlist, which include one or more drivers, is provided. The method includes operations of generating at least one look-up table for an output transient current to be based on values of input and output voltages using data available from a cell library; synthesizing analytically at least one current source model, which includes a DC component and a plurality of parasitic capacitances, using the look-up table; simulating the logic stage using the current source model to model the drivers; and obtaining characteristics of the simulated logic stage. A system and a machine-readable medium for performing the method are also provided.

Claims

1. A method for performing an analysis of at least one logic stage in a netlist, said logic stage having at least one driver, the method comprising:

a) generating at least one look-up table for an output transient current, based on values of input and output voltages, using data available from a cell library;

b) synthesizing analytically at least one current source model including a DC component and a plurality of parasitic capacitances, using said look-up table, said synthesizing said current source model including representing said DC component of said current source model using an analytical expression and curve-fitting said analytical expression to values of said output transient current available from said look-up table;

c) simulating said logic stage using said current source model to model said driver; and

d) obtaining characteristics of said simulated logic stage, wherein synthesizing said current source model further comprises computing values of said plurality of parasitic capacitances by curve-fitting said current source model to values of said output transient current available from said look-up table.

2. The method of claim 1, wherein said analytical expression is a hyperbolic tangent function, said curve-fitting to values of said output transient current comprises determining parameters defining said hyperbolic tangent function using nonlinear regression.

3. The method of claim 1, wherein obtaining characteristics comprises determining analytically a trans-conductance gain of said logic stage and identifying at least one condition of input and output voltages for reaching a pre-defined gain.

4. The method of claim 3, wherein said pre-defined gain is a maximum gain of said logic stage for a given input and output voltage range.

5. The method of claim 1, wherein obtaining characteristics comprises obtaining timing and noise characteristics of said simulated logic stage.

6. The method of claim 1, wherein generating said look-up table comprises:

a) representing analytically said input and output voltages and output transient current, respectively, as functions of time;

b) sampling said input and output voltages and output transient current at a pre-determined time interval;

c) sorting sampled output transient current values based on sampled input and output voltage values; and

d) re-sampling said output transient current at input and output voltage values of pre-defined intervals.

7. The method of claim 6, wherein representing said output transient current as a function of time comprises:

a) curve-fitting data of said output voltage, available from said cell library, to a closed-form analytical equation;

b) calculating a derivative of said closed-form analytical equation; and

c) scaling said derivative to represent said output transient current.

8. The method of claim 7, wherein curve-fitting said output voltage comprises curve-fitting said output voltage to a Weibull cumulative distribution equation.

9. The method of claim 6, wherein representing said output voltage as a function of time comprises:

a) curve-fitting data of said output transient current, available from said cell library, to a closed-form analytical equation;

b) calculating an integration of said closed-form analytical equation; and

c) scaling said integration to represent said output voltage.

10. The method of claim 9, wherein curve-fitting said output transient current comprises curve-fitting said output transient current to a quadratic equation.

11. The method of claim 1, wherein said cell library comprises current source model data conforming to a predefined format.

12. A non-transitory machine-readable medium having stored thereon a set of instructions that, when executed by a machine, result in:

a) generating at least one look-up table for an output transient current, based on values of input and output voltages, using data available from a cell library;

b) synthesizing analytically at least one current source model including a DC component and a plurality of parasitic capacitances, using said look-up table, said synthesizing said current source model comprises representing said DC component of said current source model using an analytical expression and curve-fitting said analytical expression to values of said output transient current available from said look-up table;

c) simulating said logic stage using said current source model to model said driver; and

d) obtaining characteristics of said simulated logic stage,

wherein synthesizing said current source model further comprises computing values of said plurality of parasitic capacitances by curve-fitting said current source model to values of said output transient current available from said look-up table.

13. The non-transitory machine-readable medium of claim 12, wherein said analytical expression is a hyperbolic tangent function, said curve-fitting to values of said output transient current comprises determining parameters defining said hyperbolic tangent function using nonlinear regression.

14. The non-transitory machine-readable medium of claim 12, wherein obtaining characteristics comprises determining analytically a trans-conductance gain of said logic stage and identifying at least one condition of input and output voltages for reaching a pre-defined gain.

15. The non-transitory machine-readable medium of claim 14, wherein said pre-defined gain is a maximum gain of said logic stage for a given input and output voltage range.

16. The non-transitory machine-readable medium of claim 12, wherein generating said look-up table comprises:

a) representing analytically said input and output voltages and output transient current, respectively, as functions of time;

b) sampling said input and output voltages and output transient current at a pre-determined time interval;

c) sorting sampled output transient current values based on sampled input and output voltage values; and

d) re-sampling said output transient current at input and output voltage values of pre-defined intervals.

17. The non-transitory machine-readable medium of claim 16, wherein representing said output transient current as a function of time comprises:

a) curve-fitting data of said output voltage, available from said cell library, to a closed-form analytical equation;

b)calculating a derivative of said closed-form analytical equation; and

c) scaling said derivative to represent said output transient current.

18. The non-transitory machine-readable medium of claim 17, wherein curve-fitting said output voltage comprises curve-fitting said output voltage to a Weibull cumulative distribution equation.

19. The non-transitory machine-readable medium of claim 16, wherein representing said output voltage as a function of time comprises:

a)curve-fitting data of said output transient current, available from said cell library, to a closed-form analytical equation;

b)calculating an integration of said closed-form analytical equation; and

c)scaling said integration to represent said output voltage.

20. The non-transitory machine-readable medium of claim 19, wherein curve-fitting said output transient current comprises curve-fitting said output transient current to a quadratic equation.