# Patent

## Title
Method and system for power distribution analysis

## Abstract

Disclosed are systems and methods for electrical verification of integrated circuits. Methodologies are described for verification of the power and ground distribution systems (PDS) for system-on-a-chip (SoC) and the verification of the interaction of the PDS with the behavior of integrated circuits.

## Background
CROSS-REFERENCE TO RELATED APPLICATIONS
This application claims the benefit of U.S. Provisional Application No. 60/652,919 filed Feb. 14, 2005, which is hereby incorporated by reference in its entirety.


COPYRIGHT NOTICE
A portion of the disclosure of this patent document contains material which is subject to copyright protection. The copyright owner has no objection to the facsimile reproduction by anyone of the patent document or the patent disclosure, as it appears in the Patent and Trademark Office patent files and records, but otherwise reserves all other copyright rights.
BACKGROUND AND SUMMARY
The present invention relates to power integrity verification for electrical designs. In particular, embodiments of the present invention provide methods, systems, and methodologies to validate electrical characteristics of power distribution systems (PDSs) in electrical (e.g., IC chip) designs. This type of verification can, for example, ensure that each cell and transistor in the design receive sufficient voltage to operate functionally correct.
Some embodiments of the invention provide a methodology, method, and system for multi-level hierarchical, vector-independent dynamic verification of PDS in Systems on Integrated Circuit or Systems-on-a-Chip (hereinafter SoC) with transistor level resolution. Examples of SoC include small electronic devices made out of semiconductor materials which contain various functional components such as memory, digital and analog blocks made out of passive and active electronic devices. Examples of PDS include physical wiring composed of electrical conductive segments providing electrical connection between the pins of a SoC to all active and passive devices on a SoC.
Examples of systems and methods having multi-level hierarchical verification include systems and methods having the ability to validate the PDS for a cell, macro, or block of a SoC, to extract the physical and electrical characteristic of the cell, macro or block, and to generate a model. Such a model is defined as a PDS model. A PDS model can be used for the verification of PDS at the next hierarchy level. The next hierarchy level can be a macro, a block, or the complete SoC. This methodology is called the bottom-up multi-level hierarchical verification.
Other examples for multi-level hierarchical verification include systems and methods having the ability to perform PDS verification at a specific hierarchy level using PDS models and to capture boundary conditions for each component described by a PDS model and used in the hierarchical levels of investigation. The captured boundary conditions can than be used for PDS verification at a lower hierarchical level. This methodology is called the top-down multi-level hierarchical verification.
Dynamic verification of PDS in SoC includes, for example, the capability to calculate the time-dependent voltages and currents for all segments of PDS. Static verification of PDS in SoC includes, for example, the capability to calculate the time-independent (also called average or peak) voltages and currents for all segments of PDS.
Vector-independent dynamic verification of PDS in SoC includes, for example, the capability to calculate the time-dependent power or current consumption of the components of a SoC independent of functional stimuli for the components of a SoC. Transistor level resolution includes, for example, the ability to calculate the time-dependent fluctuations of the voltages at all segments of PDS from the external connections of the SoC (power and ground pins) through all wire segments of PDS to terminals to active and passive semiconductor devices such as transistors and capacitors for all types of components of SoC.
Prior approaches for implementing power distribution analysis all suffer significant functional drawbacks. For example, systems that perform dynamic verification at transistor level require user provided functional stimuli to calculate the time-dependent current consumption. Moreover, systems that perform dynamic verification at transistor or gate level do not allow for multi-level hierarchical PDS verification. Systems that perform dynamic verification at gate level also require either user provided definitions of switching probabilities for each signal net between the components of SoC or user provided functional stimuli for primary inputs of the SoC or the components thereof. Furthermore, vector-independent dynamic verification at gate level does not provide transistor level resolution for PDS verification. In addition, prior approaches also lack the ability to calculate realistic approximation of worst-case time-dependent current consumption for SoC without user specified power constraints. Finally, prior approaches also lack means for sending effective feedback to the users about the electrical characteristic of PDS and decoupling capacitors.
Some embodiments of the present invention overcomes the limitations of prior solutions by enabling dynamic verification at the gate level requiring neither user provided definitions of switching probabilities for each signal net between the components of SoC nor user provided functional stimuli for primary inputs of SoC as well as a statistical approach to determine locally simultaneously switching components and creating worst case voltage fluctuations. Some embodiments of the instant invention are directed to both a dynamic top-down and a dynamic bottom-up multi-level hierarchical PDS verification with transistor level resolution. In addition, some embodiments of the present invention teach a vector-independent dynamic verification at gate level with transistor level resolution for PDS verification and enable the use of static PDS verification techniques to build PDS models for components of SoC and the use of these models for multi-level hierarchical dynamic PDS verification. Furthermore, some embodiments of the instant invention provide a methodology to measure the effectiveness of explicit decoupling capacitors for placement optimization as well as graphical representation. In addition, some embodiments of the present invention teach a methodology to take into account the variation of the electrical circuit behavior due to manufacturing process variations for the vector-independent calculation of current consumption for SoC.
Further details of aspects, objects, and advantages of the invention are described below in the detailed description, drawings, and claims. Both the foregoing general description and the following detailed description are exemplary and explanatory, and are not intended to be limiting as to the scope of the invention.



BRIEF DESCRIPTION OF THE DRAWINGS
The accompanying drawings are included to provide a further understanding of the invention and, together with the Detailed Description, to serve to explain the principles of the invention.
FIG. 1 illustrates an embodiment of an PDS model.
FIG. 2 shows a time-dependent current consumption waveform.
FIG. 3 shows a flow for performing vector-independent calculation of time-dependent instance based current consumption data flow according to some embodiments of the invention.
FIG. 4 shows a PDS Verification Flow according to some embodiments of the invention.
FIG. 5 describes transistor level PDS verification according to some embodiments of the invention.
FIG. 6 describes cell-based PDS verification according to some embodiments of the invention.
FIG. 7 shows a flow for PDS verification output processing according to some embodiments of the invention.
FIG. 8 shows decoupling capacitor effectiveness graphical representation data and process flow according to some embodiments of the invention.
FIG. 9 shows a decoupling capacitor aware placement optimization flow according to some embodiments of the invention.
FIG. 10 illustrates an example computing architecture with which the invention may be implemented.



DETAILED DESCRIPTION
Embodiments of the present invention provide methods, systems, and methodologies to validate electrical characteristics of power distribution systems (PDSs) in an electrical (e.g., IC chip) designs. As noted above, some embodiments of the invention provide a vector-independent methodology, method, and system for multi-level hierarchical, dynamic verification of PDS in Systems on Integrated Circuit (SoC) with transistor level resolution. Some embodiments of the invention contain several components which are described in the following description.
PDS Model
One of the purpose of the PDS models is to capture the physical as well as electrical characteristics of the PDS to serve, for example, as the basis for multi-level, hierarchical PDS verification. The PDS model captures the information used for PDS verification as well as time-varying, vector-independent gate level current consumption calculation. Both components facilitate multi-level hierarchical PDS verification, both in the bottom-up and the top-down approach. Additionally, this enables embodiments of the invention to measure, report, and optimize the effectiveness of decoupling capacitors as integral part of PDS.
According to one embodiment of the present invention, a PDS model comprises some or all of the following information for a component as shown in FIG. 1 and described below:
Physical information 102 about the segments of PDS used to connect the component within a SoC. These sets of segments are usually referred as ports of a component, and the physical information includes size, location, and layer information.
For each segment a terminal point is determined, which further defines the connection of the electrical model for a component.
An electrical network 104 describing the electrical characteristics of the PDS internal to the component. The electrical model can be as simple as a parasitic resistor network and is connected to the terminal points of the PDS model. Moreover, the parasitic network can be described by one or more RLC model or one or more subsets thereof. The electrical model can also be directly extracted from the layout information of the internal PDS. Furthermore, the size of the electrical model can be decreased by applying network reduction techniques.
Location of current sinks 106. Current sinks are in general active or passive electrical devices which are consuming current due to active operation or leakage through the semiconductor devices.
An electrical model 108 for the current sinks within the component. An electrical model can be as simple as a constant or a time-dependent current source. The model can also be described as a function of the supply voltages and the electrical environment of the component. The model can describe the absolute current for each sink or relative current strength between the sinks in a component.
Netlist connectivity information 110. The netlist connectivity information can be at the transistor level or an abstraction thereof. The netlist connectivity information includes as well electrical models describing the electrical behavior of the signal interconnect between components of the netlist. The electrical model can be as simple as a capacitor describing the parasitic signal net capacitor.
Vector-Independent Calculation of the Time-Dependent Gate Level Current Consumption
The problem being addressed by a vector-independent calculation of the time-dependent gate level current consumption methodology is to calculate the switching situation which causes the worst-case transient IR drop without the need to perform functional verification, i.e., to determine which components are switching simultaneously at which point in time in which direction based on design constraints used for and results of static timing analysis. An example of a vector-independent calculation is a calculation that is performed in a vector-less manner. An example time-dependent gate level current consumption waveform is shown in FIG. 2.
Other proposed approaches are focused solely on the determination of the worst case or peak power consumption and its associated transient current consumption waveform. While the knowledge of the peak power consumption waveform is certainly a good measure, it doesn't necessarily correlate with current consumption waveform causing the worst-cast transient IR drop.
For example, one proposed approach is a methodology to calculate the so called switching scenarios, i.e. to calculate which component is switching at which time and in which direction. The calculation in this approach is based on the timing window calculated by static timing analysis, the transition density under consideration of local logic satisfiability as well as under peak-average ratio constraints. While the proposed methodology can be used to calculate switching situations, the approach does not provide the ability to determine the transient peak power consumption. Therefore a peak-average ratio constraint is introduced as an artificial constraint to mask the deficiency of the proposed methodology. It can be easily shown that the peak-average ratio varies for different SoC as well as between different blocks of a SoC. More importantly, the method does not take into account the impact of locally simultaneously switching components causing large voltage fluctuations.
In other proposed approaches, genetic algorithms are used to calculate worst case vector sets within a given confidence range based on seed sequence(s) in combination with gate level functional simulation algorithms. One drawback of this methodology is that seed sequence needs to be provided by the user of the system, the choice of the seed sequence has strong impact on the convergence behavior of the proposed methodology. Moreover, several, usually resource intensive, functional verification cycles are required until a vector sequence approximating the worst case situation is determined in the defined confidence range. In addition, this approach is only applicable to calculate the worst-case power consumption, and is therefore not applicable to determine the worst-case transient IR drop.
Some embodiments of the present invention include a methodology that provides the ability to calculate realistic time-dependent current consumption to approximate the worst-case impact on the power distribution system. As shown in the flowchart of FIG. 3, the time and direction of the switching of each individual component 300 is calculated based on a time-dependent simultaneous switching probability function PSSO(t) 310. The time-dependent simultaneous switching probability function PSSO(t) 310 is calculated based on the switching current signature 308, the timing probability PT(t) 302, the normalized transition density PTD 304, normalized IR probability PIR 306, which are described in further details in the subsequent paragraphs.
One component of the time-dependent simultaneous switching probability function is the timing probability PT(t) 302, e.g. the probability that a specific instance will switch in a certain direction at specific point in time. One approach is to define the timing probability 302 as an uniform distribution function with PT(t)=1 within the timing window and PT(t)=0 outside. However, discrete switching time points are calculated during static timing analysis, and this information can be used to model the timing probability function 302 more realistically. In addition, statistical static timing analysis will enable the consideration of switching time variations due to process variations. The concept of timing probabilities PT(t) 302 used in this invention is the basis to take the process variations into account for the vector-independent calculation of the current consumption 300.
Another component of the time-dependent simultaneous switching probability function is the normalized transition density PTD 304, which can be calculated based on the actual transition density for a given signal net, derived either from functional simulation or through probabilistic propagation or a combination thereof, as described in “Full-chip vector-less dynamic power integrity analysis and verification against 100 uV/100 ps-resolution measurement”, Custom Integrated Circuits Conference, 2004. Proceedings of the IEEE 2004, 3-6 Oct. 2004, which is hereby incorporated by reference in its entirety.
Another component of the time-dependent simultaneous switching probability function is the normalized IR probability PIR 306, i.e., sensitivity of voltage fluctuation versus load current changes based on the resistive network representing DC characteristic of the PDS. The sensitivity of voltage fluctuations may include statistical variation of the DC characteristic caused by the process variation, and each parasitic resistive element is described by a mean value and distribution function. Therefore, the time-dependent simultaneous switching probability function PSSO(t) 310 can be expressed in the following equation:

PSSO(t)=f(PT(t),PTD,PIR))  Equation 1

Stochastic techniques such as the Monte-Carlo method based on the time-dependent simultaneous switching probability PSSO(t) 310 are used together with the switching current waveform for each individual instance to calculate the time dependent current consumption across multiple clock cycles.
Multi-Level Hierarchical Bottom-Up And Top-Down PDS Verification
FIG. 4 shows the basic PDS verification flow according to an embodiment of the invention. In this flow, the design data 402 provide the input data into the PDS verification system 404 (which comprises transistor level PDS verification system 408 and cell-based PDS verification system 410 described in more detail with respect to FIGS. 5 and 6), followed by processing of generated output data 406.
The PDS verification methodology can be applied to complete or partial design data 402. The design data 402 in one embodiment of the invention include some or all of the following information such as the design layout information, the cell library information, the environment constraints and models, and/or pre-extracted layout parasitic data. Moreover, the cell library information may comprise information such as the timing libraries, the power libraries, the PDS model libraries, the physical abstractions, and/or the transistor level description of cell contents. Finally, the environment constraints and models may comprise information such as the SoC package model data, the design operation constraints, and/or the PDS boundary conditions.
The transistor level PDS verification system 408 is described in further details in FIG. 5 and enables PDS verification at the transistor level. The transistor level PDS verification system 408 can be applied to verification and characterization of standard cells, I/O cells, analog, digital, and mixed signal custom design blocks. Furthermore, FIG. 5 shows the complete transistor level PDS verification system 408, and simplifications are possible to reduce the amount of data to be analyzed as well as captured in the PDS models. The cell-based PDS verification system 410 is described in further details in FIG. 6.
Referring to FIG. 5, the transistor level PDS verification system 408 performs the transistor level PDS verification 508 based upon the input of the design data 402. The PDS verification results are further processed in the PDS verification output processing 406. In addition, in some embodiments of the present invention, the transistor level PDS verification system further performs the transistor level parasitic extraction 504 and one or more transistor level circuit analyses 506 to achieve the desired transistor level accuracy.
FIG. 6 shows the cell-based PDS verification system 410 in one embodiment of the invention. In this cell-based PDS verification 410, the design data 402 provide the input data into the cell-based PDS verification system 410. This flow is typically applied to designs and blocks generated by place & route tools. The steps of cell-based parasitic extraction 604 and the cell-based static and/or time-dependent power consumption calculation 608 are performed at the cell level and therefore, this flow can be referred to as cell based PDS verification. Moreover, transistor level accuracy is achieved by merging the contents of PDS models for the cells with the parasitic data 606 generated in step 604 and 608. The results of the cell based PDS verification will be further processed in 406 of the PDS verification flow. The PDS verification output processing 406 contains the PDS model generation of the block or chip verified. FIG. 7 further describe the PDS verification output in more details.
Referring to FIG. 7. The PDS verification output processing phase 406 contains the generation of user consumable data and PDS verification results 704 as well as the consolidation of verification output, data compression, and data processing to build PDS models for the cell or block analyzed 706 with the transistor level PDS verification system 408. The consolidated verification output, the PDS model generated, and compressed data in 706 may be further utilized to merge with the PDS model library 708 or to establish the instance based boundary conditions 710.
The PDS model generated in this step can then be used at the next design hierarchical level to represent a block or partition within a specific design hierarchy level up to the complete SoC. The methodologies of employing the transistor level PDS verification system 408 and the cell-based PDS verification system 410 enable a bottom-up multi-level hierarchical PDS verification.
Top-down PDS verification is enabled with the methodology described herein by capturing PDS boundary conditions 710 for individual design instances. A design instance can be, for example, a partition, a block, a macro, or a cell. The instance based boundary conditions 710 are considered as environment constraints as part of the design data and can be applied at various hierarchical levels. The instance specific PDS boundary conditions 710 enable a methodology to perform PDS verification on a specific design instance taking into account the interaction between different design instances without having to perform PDS verification on the complete SoC. This methodology can be referred to as the top-down PDS verification.
Decoupling Capacitor Effectiveness and Graphical Representation of Decoupling Capacitor Effectiveness
Textual and numerical data are used to analyze the results of PDS verification in detail. However, due to the amount of data to be handled during block and full-chip PDS validation, this it is not an efficient way to provide insight about the characteristics of the PDS from a global perspective. Some embodiments of the invention provide a graphical approach to provide feedback about the effectiveness of decoupling capacitors from a global perspective. A global perspective is important in understanding the effectiveness of explicit decoupling capacitors under consideration of parasitic, embedded, and natural decoupling capacitors as well as in allowing the optimization of the placement of explicit decoupling capacitors.
Referring to FIG. 8, one of the purposes of using explicit decoupling capacitors in a PDS is to stabilize the local supply voltages for individual instances in order to minimize device switching delay variations or to avoid functional failures due to the collapse of the supply voltages. The effectiveness of decoupling capacitors 806 can therefore be measured as the ratio of the device switching delay variation Δτ 802 due to transient PDS variations versus the device switching delay τ 804 at local supply voltages determined by static PDS validation. As the switching delay is a function of the local supply voltages during the switching event, the effectiveness of explicit decoupling capacitors can therefore be approximated as a function of the ratio of the transient supply voltage variation vs. the static supply voltage at the switching cells:

I=f(Δτ,τ)≈f(ΔV(t),ΔVs)  Equation 2

Furthermore, in one embodiment of the present invention, a developed methodology includes the mapping of the effectiveness of explicit decoupling capacitor, I, into a color index 808 as shown in FIG. 8. The color index for each cell may compose, for example, a thermal map, which provides an efficient way to represent the effectiveness of decoupling capacitors globally.
Optimization of the Placement of Decoupling Capacitors
In one embodiment of the instant invention, the developed methodology to measure the effectiveness of explicit decoupling capacitors as defined in Equation 2 can be used as well as cost function together with placement optimization techniques during the placement optimization of explicit decoupling capacitors:

Φ′=Φ+ΣI2  Equation 3

Φ is the original placement optimization cost function, Φ′ is the modified cost function capturing the effectiveness of decoupling capacitors. An embodiment of a decoupling capacitor aware optimization methodology is shown in FIG. 9. The optimization cost function Φ 904 for the initial instance placement 902 is first calculated; then the modified optimization cost function Φ′ 906 is evaluated by taking into account the effectiveness of decoupling capacitors. This embodiment of the invention further defines a threshold value for a convergence criterion and determines whether the convergence criterion is met in 910. If the convergence criterion is met the current placement is thus determined to be the final placement 912. If the convergence criterion is not met this embodiment of the invention, calculates new placement and its associated optimization cost function Φ′, and repeat the above iterative process until the convergence criterion is met in 910.
System Architecture Overview
FIG. 10 is a block diagram of an illustrative computing system 1400 suitable for implementing an embodiment of the present invention. Computer system 1400 includes a bus 1406 or other communication mechanism for communicating information, which interconnects subsystems and devices, such as processor 1407, system memory 1408 (e.g., RAM), static storage device 1409 (e.g., ROM), disk drive 1410 (e.g., magnetic or optical), communication interface 1414 (e.g., modem or Ethernet card), display 1411 (e.g., CRT or LCD), input device 1412 (e.g., keyboard), and cursor control.
According to one embodiment of the invention, computer system 1400 performs specific operations by processor 1407 executing one or more sequences of one or more instructions contained in system memory 1408. Such instructions may be read into system memory 1408 from another computer readable/usable medium, such as static storage device 1409 or disk drive 1410. In alternative embodiments, hard-wired circuitry may be used in place of or in combination with software instructions to implement the invention. Thus, embodiments of the invention are not limited to any specific combination of hardware circuitry and/or software. In one embodiment, the term “logic” shall mean any combination of software or hardware that is used to implement all or part of the invention.
The term “computer readable storage medium” or “computer usable storage medium” as used herein refers to any medium that participates in providing instructions to processor 1407 for execution. Such a medium may take many forms, including but not limited to non-volatile media and volatile media. Non-volatile media includes, for example, optical or magnetic disks, such as disk drive 1410. Volatile media includes dynamic memory, such as system memory 1408.
Common forms of computer readable media includes, for example, floppy disk, flexible disk, hard disk, magnetic tape, any other magnetic medium, CD-ROM, any other optical medium, punch cards, paper tape, any other physical medium with patterns of holes, RAM, PROM, EPROM, FLASH-EPROM, any other memory chip or cartridge, or any other medium from which a computer can read.
In an embodiment of the invention, execution of the sequences of instructions to practice the invention is performed by a single computer system 1400. According to other embodiments of the invention, two or more computer systems 1400 coupled by communication link 1415 (e.g., LAN, PTSN, or wireless network) may perform the sequence of instructions required to practice the invention in coordination with one another.
Computer system 1400 may transmit and receive messages, data, and instructions, including program, i.e., application code, through communication link 1415 and communication interface 1414. Received program code may be executed by processor 1407 as it is received, and/or stored in disk drive 1410, or other non-volatile storage for later execution.
In the foregoing specification, the invention has been described with reference to specific embodiments thereof. It will, however, be evident that various modifications and changes may be made thereto without departing from the broader spirit and scope of the invention. For example, the above-described process flows are described with reference to a particular ordering of process actions. However, the ordering of many of the described process actions may be changed without affecting the scope or operation of the invention. The specification and drawings are, accordingly, to be regarded in an illustrative rather than restrictive sense.

## Claims

1. A computer implemented, vector-independent method for calculating time-dependent current consumption, comprising:
using at least one processor that is programmed for performing:
determining which electrical components are switching simultaneously at which point in time in which direction by calculating a time-dependent simultaneous switching probability function; and
calculating an instance specific, time-dependent current consumption by using at least a result of the act of calculating the time-dependent simultaneous switching probability function without performing functional verification to approximate a worst-case impact on a power distribution system, wherein
the act of calculating the instance specific, time-dependent current consumption provides multi-hierarchical level verification with transistor level resolution for an electronic circuit design, and
the electronic circuit design comprises a plurality of hierarchical levels.

2. The computer implemented method of claim 1, in which the act of calculating the time-dependent simultaneous switching probability function comprises:
defining and calculating a timing probability;
defining and calculating a transition density; and
defining and calculating a normalized IR probability.

3. The computer implemented method of claim 2, in which the act of defining and calculation said timing probability is based on one or more discrete switching time points obtained from a static timing analysis.

4. The computer implemented method of claim 2, in which the act of defining and calculating said timing probability comprises taking switching time variations due to process variations in account by using a statistical timing analysis.

5. The computer implemented method of claim 2, in which the act of defining and calculating said normalized transition density comprises defining and calculating an actual transition density derived from a functional simulation or a probabilistic propagation or a combination thereof.

6. The computer implemented method of claim 2, in which the act of defining and calculating the normalized IR probability comprises:
calculating sensitivity of voltage fluctuation; and
calculating load current changes based on a resistive network representing a plurality of DC characteristics of said power distribution system.

7. The computer implemented method of claim 6, in which the sensitivity of voltage fluctuation of the calculation of said normalized IR probability comprises one or more statistical variations of one or more DC characteristics caused by process variations.

8. The computer implemented method of claim 6, in which the resistive network representing a plurality of DC characteristics comprises one or more parasitic resistive elements each of which being described by a mean value and a distribution function.

9. The computer implemented method of claim 1, in which the act of determining which electrical components are switching simultaneously at which point in time in which direction by calculating a time-dependent simultaneous switching probability function is based on one or more static timing analyses.

10. The computer implemented method of claim 1, in which the act of calculating the instance specific, time-dependent current consumption further comprises:
using a stochastic method based on said time-dependent simultaneous switching probability calculating said time-dependent current consumption across multiple clock cycles; and
using a switching current waveform for each of one or more individual instances.

11. A computer program product that includes a computer usable storage medium having a sequence of instructions which, when executed by at least one processor, causes the at least one processor to execute a process for calculating realistic, vector-independent, time-dependent current consumption, the process comprising:
determining which electrical components are switching simultaneously at which point in time in which direction by calculating a time-dependent simultaneous switching probability function; and
calculating a realistic, instance specific, time-dependent current consumption by using a result of the act of calculating the time-dependent simultaneous switching probability function without performing functional verification to approximate a worst-case impact on a power distribution system, wherein
the act of calculating the instance specific, time-dependent current consumption provides multi-hierarchical level verification with transistor level resolution for an electronic circuit design, and
the electronic circuit design comprises a plurality of hierarchical levels.

12. The computer product of claim 11, in which said sequence of instructions causes said processor to execute a process for determining which electrical components are switching simultaneously at which point in time in which direction by calculating a time-dependent simultaneous switching probability function is based upon one or more static timing analyses.

13. The computer program product of claim 11, in which the act of calculating the time-dependent simultaneous switching probability function comprises:
defining and calculating a timing probability;
defining and calculating a transition density; and
defining and calculating a normalized ER probability.

14. The computer program product of claim 13, in which the act of defining and calculating the normalized IR probability comprises:
calculating sensitivity of voltage fluctuation; and
calculating load current changes based on a resistive network representing a plurality of DC characteristics of said power distribution system.

15. The computer program product of claim 11, in which the act of calculating the instance specific, time-dependent current consumption further comprises:
using a stochastic method based on said time-dependent simultaneous switching probability calculating said time-dependent current consumption across multiple clock cycles; and
using a switching current waveform for each of one or more individual instances.

16. A system for calculating realistic, vector-independent, time-dependent current consumption, comprising:
a computer system which comprises at least one processor and is programmed for performing:
determining which electrical components are switching simultaneously at which point in time in which direction by calculating a time-dependent simultaneous switching probability function; and
calculating a realistic, instance specific, time-dependent current consumption by using a result of the act of calculating the time-dependent simultaneous switching probability function without performing functional verification to approximate a worst-case impact on a power distribution system, wherein
the act of calculating the instance specific, time-dependent current consumption provides multi-hierarchical level verification with transistor level resolution for an electronic circuit design, and
the electronic circuit design comprises a plurality of hierarchical levels.

17. The system of claim 16, in which the computer system that is programmed for calculating the time-dependent simultaneous switching probability function is further programmed for performing:
defining and calculating a timing probability;
defining and calculating a transition density; and
defining and calculating a normalized IR probability.

18. The system of claim 17, in which the computer system that is programmed for defining and calculating the normalized IR probability is further programmed for performing:
calculating sensitivity of voltage fluctuation; and
calculating load current changes based on a resistive network representing a plurality of DC characteristics of said power distribution system.

19. The system of claim 16, in which the computer system is further programmed for performing:
using a stochastic method based on said time-dependent simultaneous switching probability calculating said time-dependent current consumption across multiple clock cycles; and
using a switching current waveform for each of one or more individual instances.