11.4 Multi Corner Multi Mode Optimization with Voltage Scaling Designs

It is commonplace in modern SoC designs to have a variety of functional modes. With multi-voltage design we introduce a number of additional modes to the design, including various performance levels and sleep modes, such as light sleep, hibernate and complete shutdown. These additional modes need to operate at a number of different corners (process, voltage and temperature points). The combination of these multiple modes each operating at different corners can be termed as scenarios. During the implementation process we need to both optimize and analyze the design for each of these scenarios.

For a dynamic voltage scaling design, we are concerned with ensuring full device operation at each of the various performance levels that are specified for the design. Specifically, we need to ensure that as we scale the voltage in conjunction with scaling the frequency that we have an optimal implementation at each supported combination of voltage and frequency. In a single voltage design, our worst case corner (for setup) is usually at the lowest voltage, highest temperature and worst case process. However, as we scale the performance levels in our design we may find that our worst case corner is some intermediate combination of voltage and frequency that does not reside at the edge of our operating window. Identification of this corner is important and an integral part of the implementation process.

This process is managed in the EDA tools through the use of multi-corner, multimode analysis.