Minimal Energy Asynchronous Dynamic Adders

In battery-operated portable or implantable digital devices, where battery life needs to be maximized, it is necessary to minimize not only power consumption but also energy dissipation. Typical energy optimization measures include voltage reduction and operating at the slowest possible speed. We employ additional methods, including hybrid asynchronous dynamic design to enable operating over a wide range of battery voltage, aggregating large combinational logic blocks, and transistor sizing and reordering. We demonstrate the methods on simple adders, and discuss extension to other circuits. Three novel adders are proposed and analyzed: A two-bit PTL adder and two dynamic two-bit adders. Circuit simulations on a 0.18μm process at low voltage show that leakage energy is below 1 % and that short-circuit energy depends on circuit topology and can be as high as 50 % of total energy when operating at low voltage and low fanout. The proposed adders achieve up to 40 % energy savings relative to previously published results, while also operating faster.