2021 Volume 18 Issue 6 Pages 20210065
This paper proposes a ring oscillator (ROSC) for extremely low-voltage LSI applications. The ROSC consists of dedicated low-voltage stacked body bias inverters (SBBIs) that are based on the conventional self-bias inverter (SBI) and stacked inverter (SI). The proposed SBBI employs the advantages of both SBI and SI to oscillate at extremely low supply voltage. The voltage gain of the proposed SBBI is improved by controlling main inverter’s supply (VDD and Gnd) and body-bias voltages, by using stacked and feedback inverters. The novelty of our proposed SBBI is in the combination of the conventional low-voltage circuit design techniques and its demonstration at extremely low supply voltage. Simulated and measured results in a 0.18-µm CMOS process with deep n-well option demonstrated that the proposed ROSC can operate at extremely low supply voltage of 35 mV and generate a clock with an 88% voltage swing from an input supply voltage of 50 mV. To the best of the authors’ knowledge, this is the lowest supply voltage CMOS ring oscillator ever reported.