A Multi-Folded MCML for Ultra-Low-Voltage High-Performance in Deeply Scaled CMOS

In this paper we propose a novel approach called Multi-Folded (MF) MOS Current Mode Logic (MCML) which can be applied to a generic MCML gate (i.e., with a fan-in higher than two). The idea is implemented by alternating NMOS and PMOS differential pairs and properly introducing current mirrors between the adjacent levels of logic. The proposed approach allows a minimum power supply equal to the one of a MCML inverter and we show analytically the advantages in terms of speed and power consumption against the conventional implementation. The approach has been validated with post-layout simulations considering a commercial 28nm FD-SOI CMOS technology and a supply voltage as low as 0.6V. In particular, OR/NOR gates with 3, 4, and 5 inputs implemented both with the conventional 2-inputs MCML gates implementation (Fin2) and the proposed MF MCML have been compared. Results show a reduction in the power consumption of the MF MCML equal to 3/4, 2/3 and 5/8 for the OR3, OR4 and OR5 logic functions respectively. Moreover, in terms of speed the Fin2 implementation has a delay at least 1.4 worst than the MF MCML, but is generally 1.7 worst than the proposed MF MCML gate. In this paper we have presented a novel approach which allows to implement MCML gates with a fan-in higher than 2 while keeping the minimum supply voltage as low as the one of a conventional MCML inverter. The proposed methodology, named Multi Folded MCML, born out by a generalization of the Folded MCML previously proposed by authors. The approach has been compared against the conventional Fin2 implementation (suited to implement arbitrarily logic function with a low power supply) both in terms of power consumption and propagation delay. The results have clearly demonstrated the advantages provided by the MF MCML. In particular, OR/NOR gates with 3-, 4-, and 5-inputs have been compared considering a commercial 28nm FD-SOI CMOS technology and a supply voltage as low as 0.6V. Post layout simulation results have shown that the MF gates outperform the conventional implementations in terms of propagation delay for all the considered logic functions. In particular, the propagation delay of the Fin2 implementation has been shown to be at least 1.4 times higher than the one of the MF MCML implementation and even 2 times higher for other logic functions. The power consumption of the MF gates has been shown to be 3/4, 2/3 and 5/8 than the one of the Fin2 implementations for the OR3, OR4 and OR5 logic functions respectively. Hence, the only drawback of the propose techniques seems due to a more complex design procedure.