Extended Exploration of Low Granularity Back Biasing Control in 28nm UTBB FD-SOI Technology

Recently, we proposed a low-granularity back-bias control technique [1] optimized for the ultra-thin body and box (UTBB) fully-depleted silicon-on-insulator (FD-SOI) technology. The technique was preliminary evaluated through the design of a low-voltage 8-bit ripple carry adder (RCA), showing very competitive energy and delay values. In this paper, the characteristics of the low-granularity back-biasing control are explored considering as benchmarks basic logic gates as well as adders with different bit lengths. All the designed circuits were compared to their equivalent dynamic threshold voltage MOSFET (DTMOS) and conventional CMOS designs. The higher efficiency of low granularity body bias control is emphasized by the single well layout strategy, offered by the 28 nm UTBB FD-SOI technology, thus leading our approach to achieve competitive silicon area occupancy along with significant performance and energy improvements. More precisely, post-layout simulations have demonstrated that circuits designed according the suggested strategy, can achieve a delay reduction of 33% compared to conventional CMOS designs, whereas the energy consumption can be reduced down to 46% compared to DTMOS solutions, for a supply voltage of 0.4V. These results were obtained while maintaining robustness against process and temperature variations.