An Ultra-low Power Robust Kogge- Stone Adder at Sub-threshold Voltages for Implantable Bio-medical Devices

The growing demand for energy constrained applications and portable devices have created a dire need for ultra-low power circuits. Implantable biomedical devices such as pacemakers need ultra-low power circuits for a better battery life for uninterrupted biomedical data processing. Circuits operating in subthreshold region minimize the energy per operation, thus providing a better platform for energy constrained implantable biomedical devices. This paper presents 8, 16 and 32-bit ultra-low power robust Kogge-Stone adders with improved performance. These adders operate at subthreshold supply voltages which can be used for low power implantable bio-medical devices such as pacemakers. To improve the performance of these adders in sub-threshold region, forward body bias technique and multi-threshold transistors are used. The adders are designed using NCSU 45nm bulk CMOS process library and the simulations were performed using HSPICE circuit simulator. Quantitative power-performance analysis is performed at slow-slow (SS), typical-typical (TT) and fast-fast (FF) corners clocked at 50 KHz for temperature ranging from 25̊C to 120 ̊C. For a supply voltage 0.3V, all the adders had the least PDP. Using 0.3V as the supply voltage, multi threshold voltage and forward body biasing techniques were applied to further improve the performance of the adders. The PDP obtained using the forward body biasing technique shows an effective improvement compared to high threshold voltage and multi threshold voltage techniques. The forward biasing technique maintains a balance between delay reduction and increase in average power, thus reducing the power delay product when compared to the other two techniques.