Voltus-Fi: Faithful Custom and Analog EMIR and Power Analysis

First things first. Voltus and Voltus-Fi are two separate products. They are both used for EMIR analysis, Voltus for digital design and Voltus-Fi for analog design (or custom transistor-level digital), or, in conjunction with with Voltus for mixed-signal designs. EMIR stands for electromigration and IR drop analysis. The "Fi" in Voltus Fi either stands for "fidelity" as in "Hi-Fi" or it is the Latin word for faithful, as in the US Marine's motto "Semper Fidelis" (always faithful) often abbreviated to "Semper Fi", your choice. Either way, it is that the analysis is accurate. The full-name is Cadence Voltus-Fi Custom Power Integrity Solution.

When current flows through high-resistance metal (and all metal has some resistance), then there are two things to worry about. Electromigration is a phenomenon where the electrons flowing through the metal, usually copper these days, literally cause the ions of metal to move in the direction of the current since some of the momentum of the electrons gets transferred. The problem with this is that if there is a narrow neck in the metal, the current there will be higher. This, in turn, causes metal to move away from the neck making it even narrower. This is positive feedback: the narrower the neck gets, the more the metal migrates and the neck gets narrower still. Eventually it can open completely and (probably) will cause a hard failure of the chip. The phenomenon is worse at higher temperatures, so in military and automotive markets it is necessary to be even more cautious. Each process has complex rules for exactly how much current is allowed in each layer, each via and so on. You would think that this would be symmetric, current flowing one way through a via would have the same limit as flowing in the other, but modern processes are so complex now that even that is not true.

The other effect of a current flowing through resistive metal is that the voltage will drop. This can cause the voltage, especially for the power supply, to drop so low that it is under the spec voltage for the cells in the design and can cause intermittent failures as a result. Additional analysis is needed for designs where blocks are powered down to make sure that the inrush currents when a block is re-activated don't cause the voltage to sag so much on other parts of the chip that they malfunction.

Another aspect of analysis of currents and resistances is the power dissipated. In turn, this contributes to an increase in temperature that can be examined by creating a thermal map, a two-dimensional representation of the SoC with the temperature indicated from blue (cold) to red (hot). FinFETs have additional thermal issues due to self-heating effects.

The way that Voltus and Voltus-Fi are linked is through an interface known as PGV for Power Grid View. This is a macro model that Voltus-Fi creates doing a full analysis in the analog world, but that can be made use of by Voltus when doing analysis of the whole chip (or a mixed-signal block) and can also be used by Innovus for ECO.

Voltus-Fi can also be used for custom power signoff. This gives SPICE-accurate transistor-level power signoff. It is integrated into the Virtuoso flow with extraction, EMIR, simulation (using Spectre APS, Accelerated Parallel Simulator), visualization, analysis, debug and fix. Plus, as already said above, it can generate the PGV for use in the digital implementation flow.

One user of Voltus-Fi is Phison Electronics. Phison is a company based in Taiwan that primarily manufactures controllers for NAND flash memories. It used Voltus-Fi to achieve silicon-proven accuracy on EMIR checks for its most advanced flash controller chips. It reduced its tapeout schedule by eight weeks, improving time to market by 40 percent, while also increasing overall product reliability. But perhaps most important is making sure not to miss problems that might lead to respins. As Aw Yong Chee Kong, president at Phison Electronics, put it:

Using a low-power design methodology and maintaining power-grid integrity have become critical design requirements for signoff, especially at lower process nodes. By incorporating Voltus-Fi into our design flow, Phison engineers have been able to find design weaknesses such as potential voltage drop and electromigration failures, preventing costly silicon re-spins.

Learn more about the Voltus-Fi Custom Power Integrity Solution.