Published by David Ratchkov, June 8, 2020
IEEE2416 'Standard for Power Modeling to Enable System-Level Analysis' became official in May 2019. Among its many cool aspects it defines a new way of modeling leakage. What is it and how does it differ from Liberty?
In the classical method for measuring circuit leakage, we put a circuit in a predefined quiescent state and measure currents on supplies and input pins. Those currents are leakage. We don’t know what type of leakage it is or where in the circuits the leakage comes from. But we can very quickly find out the total leakage of a complex circuit by just summing up the pin leakages. This is how Liberty data for standard cells and memories gets generated today and how it gets used by the power analysis tools. In many ways, power analysis tools of today are just glorified calculators.
IEEE2416 specifies Contributor models and specifically for leakage it is PowerContributor. PowerContributor models circuit detail only - it tells us how many transistors are there and what their terminal voltages are at a given steady state, but leaves the transistor leakage calculations for a later time. Calculating cell leakage is then done every time we need to know cell leakage. That is actually a very good thing. You see, leakage is very strongly dependent on Process, Voltage and Temperature. The first benefit is that we longer need a library for every PVT point we are interested in - we can just calculate the leakage ourselves, at the PVT we desire.
Let me repeat that - with one library we get leakage leakage at any PVT point.
One library. Any PVT.
A user no longer needs to have multiple libraries for power. Unnecessary are all scaling factors which you might have needed to derive. Any user of the model can now get leakage at their desired PVT. This includes all Reliability Engineers, for whom I have deep respect, and who’d always need leakage at extreme corners, such as 150C and +40% supply.
But that’s not all.
Calculating leakage per transistor later, means we can specify PVT per transistor as well. This opens the door to very interesting capabilities. Need to model self heating? Check. Need to model per instance IR drop? Check. Need to model process variation? Check. Need to optimize design for leakage yield? Check.
And this is still not all.
Ask yourself this - what if I am using different models to generate the model and to calculate the leakage? The answer is simple - you just found out a way to get leakage for a technology for which you don’t have a library yet.
We talked about calculating leakage for every transistor. But just how many calculations we need to make? Not that many actually. At library level, the set of possible transistor states is very limited. A properly architected tool would cache the calculations and reuse them. Compared to library characterization? It is noise.
PowerMeter™ supports the entire life cycle of the IEE2416 models. Generation of models is a fast, fully automated process relying on existing library data and requiring minimal user input, only as such to identify the location of the files. Usage is trivial - just tell the tool, in the of many available ways, how many instances of cells there are, and it will tell report what their leakage is. Of course, you can specify any number of PVT points and all results will be generated in parallel.
The full automation coupled with modern intuitive UI flattens the learning curve.
Contact us to find more details how advanced power modeling with IEE2416 can help lower reduce your design power.