All-digital on-chip heterogeneous sensors for tracking the minimum energy point of processors

Dynamically scaling the supply voltage (VDD) and the threshold voltage (VTH) is one of the most effective approaches for reducing the energy consumption of processors. However, since the best pair of VDD and VTH, which minimizes the energy consumption of processors is strongly dependent on the operating condition such as an activity factor and a performance required for the processor, it is not trivial to find the best pair of the voltages at runtime when the operating condition widely varies. With all-digital on-chip heterogeneous sensors, we propose a simple runtime method to accurately identify the best pair of VDD and VTH, which minimizes the energy consumption of a processor under a specific operating condition which is determined by a process variation, an activity factor, and a performance requirement for the processor. Measured results for a 32-bit RISC processor integrating the heterogeneous sensors show that the proposed method successfully tracks the minimum energy operating point (i.e. the best pair of VDD and VTH) of the processor even in a case that the operating condition widely varies.