Optimal supply and threshold scaling for subthreshold CMOS circuits

With technology scaling, power supply and threshold voltage continue to decrease to satisfy high performance and low power requirements. In the past, subthreshold CMOS circuits have been inadequate for high performance applications, but have been used in applications that require ultra low power dissipation. Many applications including medical and wireless applications, require ultra low power dissipation with low-to-moderate performance (10kHz-100MHz). In this work, using BSIM3 models, the performance and energy dissipation of 0.18-mum CMOS circuits for the range of V-dd=0.1-0.6V and V-th=0-0.6V are analyzed to show that subthreshold CMOS circuits can be used in low performance applications. A simple characterization circuit is introduced which can be used to evaluate the performance and energy dissipation for a given process under varying activity. These results are useful in circuit design by giving insight into optimal voltage supply and threshold voltage operation for a given application specification. Characterization results show that operation at the optimal V-dd-V-th voltage levels can lead to an order of magnitude energy savings. Also additional analysis into V-th and temperature variations is included.