A 23-pW NMOS-Only Voltage Reference With Optimum Body Selection for Process Compensation

This brief presents an NMOS-only voltage reference with small process variations for ultra-low-power applications. All MOSFETs work in the subthreshold region and are biased by the leakage current of the NMOS transistor manufactured in Deep-N-Well (DNW). By fitting the variations of threshold voltage ( $\text{V}_{\mathrm{ TH}}$ ) from slow/fast corners to typical corners linearly, an optimum body selection (OBS) is proposed to reduce the impact of the process variations from $\text{V}_{\mathrm{ TH}}$ or $\Delta \text{V}_{\mathrm{ TH}}$ with the aid of the body effect. The proposed design was fabricated in a 0.18- $\mu \text{m}$ CMOS process, together with a baseline design without using the OBS. Based on the 25-chip measurement results, the output voltage variation of the proposed design is $0.0035 \sigma /\mu $ , which is 61% smaller than that of the baseline design. Besides, for the proposed design with the OBS, the power consumption is 23pW (27°C), while the die area is 0.003mm2. The temperature coefficient is 52ppm/°C in a temperature range from 0°C to 85°C without trimming. The line sensitivity is 0.03%/V, and the power supply rejection ratio is 47dB at 100Hz.