An ultra-low power robust Kogge-Stone adder at sub-threshold voltages for implantable bio-medical devices
The growing market for energy constrained applications and portable devices, created a dire need for circuits operating at ultra-low power. Many portable biomedical devices require ultra-low power and a better battery life for uninterrupted biomedical data processing. Circuits operating in sub-threshold region minimize the energy per operation and thus provide a better platform for energy constrained portable biomedical devices. In this thesis, an 8, 16 and 32 bit ultra-low power robust Kogge-Stone adder at subthreshold supply voltages is presented for implantable biomedical devices like cardiac pacemakers. On reducing the supply voltage, minimum operating point for the Kogge-Stone adder is obtained at a supply voltage lower than that of the threshold voltage of the transistor. Maintaining a good tradeoff between power consumption and performance always remained as an important metric. Hence, for the performance enhancement of the adder at the minimum operating point, techniques such as forward body bias and multi-threshold voltage are exploited. The adder is designed using NCSU 45nm process library at SS, TT and FF corners & ASU 32nm Low Power CMOS technology model and clocked at 50 KHZ for implantable biomedical applications. HSPICE simulations are run at various process corners for temperatures ranging from 25°C to 120°C. A comparative analysis of the different techniques proposed for the performance improvement of the subthreshold Kogge-Stone adder with the standard circuit counterparts is presented. Finally, the achieved results are compared with the previously published work.