Correlation
With separate controls for power, thermal, and IR-drop analyses, InVar can be used in either native or compatibility mode.
In native mode, InVar operates in a continuous space of voltage and temperature. This is the unique feature that allows InVar to deliver real life physical measurements.
No other sign-off tool on the market can provide real life accuracy of individual voltage and temperature assigned to every element of IC design. All other analysis tools operate in corners without taking into account mutual inter-dependency of power, temperature, voltage drop, and timing analysis processes. Even SPICE simulators have no dynamic temperature feedback built into the tool.
In compatibility mode, InVar uses corner based analysis approach for compatibility with other sign-off tools. This mode is important if user wants to do correlation of analysis results.
Correlation with other analysis tools
Majority of the existing analysis tools just bundle standalone analysis engines and perform particular types of analysis separately, and that causes inaccuracy of analysis results.
Unfortunately, analysis “in corners” is a “standard” way of doing analysis. InVar can work in this mode also, and it is important for InVar to correlate with other sign-off tools in this mode.
Power correlation in compatibility mode
Each dot represents the same cell with reference power by X and power reported in InVar by Y.
Linear approximation gives:
Y = 1.016 * X - 0.016
Maximum difference = 1.128 uW
IR-drop correlation in compatibility mode
Each dot represents the same cell with reference voltage drop by X and voltage drop reported in InVar by Y.
Linear approximation gives:
Y = 1.046 * X + 0.005
Maximum difference = 0.11 mV
For this particular design, correlation averages out to 1% for power analysis and to 4.6% for IR-drop analysis in compatibility mode.
In native analysis mode ( i.e., concurrent analysis of power, temperature, and IR-drop in continuous analysis space), correlation results become very different. Note: Reference sign-off still uses old good corner-based approach.
Power correlation in native mode
Each dot represents the same cell with reference power by X and power reported in InVar by Y.
Linear approximation gives:
Y = 1.136 * X - 0.049
Maximum difference = 9.055 uW
IR-drop correlation in native mode
Each dot represents the same cell with reference voltage drop by X and voltage drop reported in InVar by Y.
Linear approximation gives:
Y = 1.321 * X - 0.082
Maximum difference = 1.86 mV
For this particular design, correlation averages out to 13% difference for power analysis and to 32% difference for IR-drop analysis. This is significantly larger than difference between InVar and reference sign-off data in compatibility mode.
Conclusion
If user is required to perform standard corner based analysis, InVar will replace up to four tools and provide accuracy that is on a par with other sign-off analysis tools. With concurrent analysis turned on (to provide accurate simulation of real world behavior), difference with other tools becomes significantly larger. That means that “standard” analysis is not precise for modern technology nodes, and only InVar satisfies demand for more accurate and reliable analysis.
