UBC Theses and Dissertations

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UBC Theses and Dissertations

Low power System-on-Chip design using voltage islands : from application to floorplan Sengupta, Dipanjan


With the continued trend in device scaling and the ever increasing popularity of hand held mobile devices, power has become a major bottleneck for the development of future generation System-on-Chip devices. As the number of transistors on the SoC and the associated leakage current increases with every technology generation, methods for reducing both active and static power have been aggressively pursued. Starting with the application for which the SoC is to be designed, the proposed design flow considers numerous design constraints at different steps of design process and produces a final floorplanned solution of the cores. Voltage Island Design is a popular method for implementing multiple supply voltages in a SoC. Use of multiple threshold voltages with power gating of cores is an attractive method for leakage power reduction. This thesis addresses the design challenges of implementing multiple supply and threshold voltage on the same chip holistically with the ultimate goal for maximum power reduction. Specifically, given the power-state machine (PSM) of an application, the high power and low power cores are identified first. Based on the activity of the cores, threshold voltage is assigned to each core. The next step is to identify the suitable range of supply voltage for each core followed by voltage island generation. A methodology of reducing the large number of available choices to a useful set using the application PSM is developed. The cores are partitioned into islands using a cost function that gradually shifts from a power-based assignment to a connectivity-based one. Additional design constraints such as power supply noise and floorplan constraints can offset the possible power savings and thus are considered early in the design phase. Experimental results on benchmark circuits prove the effectiveness of the proposed methodology. On average, the use of multiple VT and power gating can reduce almost 20% of power compared to single VT. A proper choice of supply voltages leads to another 4% reduction in power. Compared to previous methods, the proposed floorplanning technique on average offers an additional 10% power savings, 9% area improvement and 2.4X reduction in runtime.

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