A 34-mV Startup Ring Oscillator Using Stacked Body Bias Inverters for Extremely Low-Voltage Thermoelectric Energy Harvesting

A ring oscillator (ROSC) for extremely low-voltage thermoelectric energy generators is presented. The ROSC is composed 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 $(V_{\mathrm{D}\mathrm{D}})$. The voltage gain $\vert A_{\mathrm{I}\mathrm{N}\mathrm{V}}\vert$ of our proposed SBBI is improved and enhanced by controlling main inverter's supply $(V_{\mathrm{D}\mathrm{D}}$ and Gnd) and body-bias voltages, by using stacked and feedback inverters. Simulated results using a standard 0.18 $\mu \mathrm{m}$ CMOS process with deep N-well option showed that our proposed ROSC could oscillate at extremely low $V_{\mathrm{D}\mathrm{D}}$ of 34 mV and generate a clock pulse with a 88% voltage swing from an input $V_{\mathrm{D}\mathrm{D}}$ of 50 mV.