Novel Ultra-Low-Voltage Flip-Flops: Near-Vth Modeling and VLSI Integration

This paper presents two novel ultra-low-voltage (ULV) Single-Edge-Triggered flip-flops (SET-FF) based on the True-Single-Phase-Clocking (TSPC) scheme. By exploiting the TSPC principle, the overall energy efficiency has been improved compared to the traditional flip-flop designs while providing fully static, contention-free functionality to satisfy ULV operation. At 0.5V near-Vth level in 65nm bulk CMOS technology, the proposed SET-FFs demonstrate up to 11-45% and 7-20% of energy efficiency at 0% and 100% data activity rates compared to the best known SET-FFs. The proposed SET-FF can safely operate down to 0.24V of supply voltage without corrupting rail-to-rail voltage levels at its internal nodes. The integration of proposed SET-FFs in a 320-bit parallel shift register demonstrated up to 33% of clock network power, 17-39% of register power reductions compared to the state-of-the-art and commercial standard-cells at near-Vth level. In addition to these merits, with the aid of parasitic modeling, this paper re-evaluates the vital performance metrics of SET-FFs at near-Vth voltage domain, improving their characterization accuracy and enabling the VLSI integration for commercial end-use.