Exploiting Dual Mode Logic for Approximate Computing

The unique ability of dual-mode logic (DML) to self-adapt to computational needs by providing high speed and/or low-energy consumption is demonstrated for the first time for exact or approximate operations suitable for both error-resilient and exact applications. At the gate level, the DML design offers the possibility to operate either in the static mode to save energy or in the dynamic mode to increase speed, albeit with higher delay or energy consumption, respectively. In this paper, these two operation modes of the DML gates are optimally managed by a self-adjustment mechanism to increase speed or reduce the energy at run time, while changing the design accuracy. As a test case, a DML Carry Look Ahead adder (CLA) based in Dual Mode Logic (DML) that can operate in exact and approximate mode with the same frequency has been proposed. Through comparisons with CMOS-based alternative at various operating voltages, the advantages of the ADMLCLA are showcased. In static mode, the ADML-CLA presents less energy consumption of about 16% to 21%. In mixed mode, the ADML-CLA achieves delay reduction of 21% to 25%. The effectiveness of the controller in saving energy is demonstrated, with the ADML-CLA consuming less energy than CMOS when static signals are prevalent. Monte Carlo simulations highlight the lower average delay and deviation of the ADML-CLA compared to CMOS. Evaluation at a nominal voltage of 0.4V shows that the ADML (mixed) outperforms CMOS in terms of energy-delay product (EDP) in both exact and approximate modes.