Independent N-Well And P-Well Biasing For Minimum Leakage Energy Operation

This paper proposes a method for minimizing leakage energy consumption under a specific supply voltage and a delay constraint by independently tuning threshold voltages of nMOSFETs and pMOSFETs with body-biasing. We first show a necessary and sufficient condition for the minimum leakage energy operation of a circuit under a delay constraint. We next show that the condition can be identified by a ratio of the leakage currents drawn through an nMOSFET and a pMOSFET in a leakage monitor circuit integrated with the targeting circuit. The leakage current ratio can be monitored at runtime using the leakage monitor. Assuming a constant supply voltage, it is thus possible to minimize the total energy consumption of the circuit by independent tuning of n-well and p-well bias voltages so that the leakage current ratio tracks the predetermined value while keeping the delay constraint. The proposed strategy is experimentally verified by measurements using a 32-bit RISC processor integrating the leakage monitor on the same die fabricated with a 65 nm CMOS process.