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

Dynamically scaling the supply voltage (V
_DD
) and the threshold voltage (V
_TH
) is one of the most effective approaches for reducing the energy consumption of processors. However, since the best pair of V
_DD
and V
_TH
, 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 V
_DD
and V
_TH
, 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 V
_DD
and V
_TH
) of the processor even in a case that the operating condition widely varies.