Process Tolerant Ã\x9f-ratio Modulation for Ultra-Dynamic Voltage Scaling

Most wireless and hand-held gadgets work in burst mode, and the performance demand varies with time. When the performance requirement is low, the supply voltage can be dithered and the circuit can enter from superthreshold region to subthreshold region (V_dd < V_T). Such ultra dynamic voltage scaling (UDVS), where the supply voltage switches from 1.2V to 200mV (say), enables remarkable decrease in power consumption with "acceptable" performance penalty in the non-burst mode of operation. However, subthreshold operation is very sensitive to process variation (PV) due to the reduced noise margin, and may not work properly unless corrective measures are taken. In this paper, the authors model the trip voltage in both subthreshold and superthreshold regions, and analyze the impact of PV in UDVS. They also propose a circuit design technique such that the same logic gate can efficiently operate in both superthreshold and subthreshold regions under PV. The authors do that by modulating the beta-ratio (P-to-N ratio) of the logic gates. By proper beta-ratio modulation, the authors show that the proposed methodologies can lower energy dissipation per cycle by more than an order of magnitude (42times) in non-burst mode with reduced impact to PVs