Synthesizing current source driver model for analysis of cell characteristics
View Patent ↗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.
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.